ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
Filter
  • American Association of Petroleum Geologists (AAPG)  (92,538)
  • 1
    Journal cover
    Unknown
    American Association of Petroleum Geologists (AAPG) | GeoScienceWorld | formerly Blackwell Publishing
    Online: 4.1997 – (GFZ only)
    Publisher: American Association of Petroleum Geologists (AAPG) , GeoScienceWorld , formerly Blackwell Publishing
    Print ISSN: 1075-9565
    Electronic ISSN: 1526-0984
    Topics: Geography , Geosciences
    Keywords: GeoScienceWorld
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 2
    Journal cover
    Unknown
    American Association of Petroleum Geologists (AAPG) | GeoScienceWorld
    Online: 84.2000 – (GFZ only)
    Print: 34(12).1950 – 93(4).2009 (Location: A17, Kompaktmagazin, 9/7 - 10/6)
    Publisher: American Association of Petroleum Geologists (AAPG) , GeoScienceWorld
    Print ISSN: 0016-7606 , 0149-1423
    Electronic ISSN: 1943-2674
    Topics: Geosciences
    Keywords: GeoScienceWorld ; petrology ; Erdöl ; Erdölgeologie ; Erdölgewinnung ; Erdgas ; Erdgasgeologie
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 3
    Publication Date: 2016-01-17
    Description: The Arctic changes rapidly in response to global warming and is expected to change even faster in the future (IPCC 2001, 2007, 2013). Large areas of the shelves and continental slopes bordering the Arctic Ocean are characterized by permafrost and the presence of gas hydrates. Future global warming and potential hydrate dissociation in the Arctic Ocean challenge the slope stability of these areas. This may lead to slope failures. The first, and so far only reported, large-scale slope failure in the Arctic Ocean is the Hinlopen/Yermak Megaslide (HYM), which is located in front of the Hinlopen glacial trough north of Svalbard. During cruise MSM31 onboard the German R/V MARIA S. MERIAN we investigated this giant slope failure and the deeper structure of the Sophia Basin in detail to elucidate the potential causes of the main and following failure events as well as to test existing hypotheses on the generation of this giant submarine landslide. We studied the megaslide and the adjacent so far not failed shelf areas by means of multibeam swath bathymetry, Parasound sediment echo sounder, low- and high-resolution multichannel seismic reflection profiling. The seismic data image bottom-simulating reflectors beneath not failed areas of the slope, as well as a buried gas escape pipe. On the shelf, shallower than the gas hydrate stability zone, we observed widespread gas seepage as flares in the Parasound echo sounder data. These flares rise from a seafloor highly disturbed by iceberg scouring. Therefore, we could not identify pockmarks in the multibeam data. At one location, we sampled a flare by means of a CTD probe close to the seafloor and proofed that the emanating gas has a high methane concentration. The new data indicate that the existence of gas and gas hydrates beneath the shelf north of Svalbard was one key factor causing slope instability in the past and may also cause further slope failures in the future.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 4
    Publication Date: 2016-01-21
    Description: The modern polar cryosphere reflects an extreme climate state with profound temperature gradients towards high-latitudes. It developed in association with stepwise Cenozoic cooling, beginning with ephemeral glaciations and the appearance of sea ice in the late middle Eocene. The polar ocean gateways played a pivotal role in changing the polar and global climate, along with declining greenhouse gas levels. The opening of the Drake Passage finalized the oceanographic isolation of Antarctica, some 40 Ma ago. The Arctic Ocean was an isolated basin until the early Miocene when rifting and subsequent sea-floor spreading started between Greenland and Svalbard, initiating the opening of the Fram Strait / Arctic-Atlantic Gateway (AAG). Although this gateway is known to be important in Earth’s past and modern climate, little is known about its Cenozoic development. However, the opening history and AAG’s consecutive widening and deepening must have had a strong impact on circulation and water mass exchange between the Arctic Ocean and the North Atlantic. To study the AAG’s complete history, ocean drilling at two primary sites and one alternate site located between 73°N and 78°N in the Boreas Basin and along the East Greenland continental margin are proposed. These sites will provide unprecedented sedimentary records that will unveil (1) the history of shallow-water exchange between the Arctic Ocean and the North Atlantic, and (2) the development of the AAG to a deep-water connection and its influence on the global climate system. The specific overarching goals of our proposal are to study: (1) the influence of distinct tectonic events in the development of the AAG and the formation of deep water passage on the North Atlantic and Arctic paleoceanography, and (2) the role of the AAG in the climate transition from the Paleogene greenhouse to the Neogene icehouse for the long-term (~50 Ma) climate history of the northern North Atlantic. Getting a continuous record of the Cenozoic sedimentary succession that recorded the evolution of the Arctic-North Atlantic horizontal and vertical motions, and land and water connections will also help better understanding the post-breakup evolution of the NE Atlantic conjugate margins and associated sedimentary basins.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 5
    Publication Date: 2019-07-16
    Description: Petroleum systems located at passive continental margins received increasing attention in the last decade mainly because of deep- and ultra‐deep-water hydrocarbon exploration and production. The high risks associated with these settings originate mainly from the poor understanding of inherent geodynamic processes. The new priority program SAMPLE (South Atlantic Margin Processes and Links with onshore Evolution), established by the German Science Foundation in 2009 for a total duration of 6 years, addresses a number of open questions related to continental breakup and post‐breakup evolution of passive continental margins. 27 sub‐projects take advantage of the exceptional conditions of the South Atlantic as a prime “Geo‐archive.” The regional focus is set on the conjugate margins located east of Brazil and Argentina on one side and west of Angola, Namibia and South Africa on the other (Figure 1) as well as on the Walvis Ridge and the present‐day hotspot of Tristan da Cunha. The economic relevance of the program is demonstrated by support from several petroleum companies, but the main goal is research on fundamental processes behind the evolution of passive continental margins.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Book , NonPeerReviewed
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 6
    Publication Date: 2016-12-16
    Description: Abnormal pressures are encountered during exploration drilling in different parts of Krishna–Godavari Basin on the east coast of India. The nature and stratigraphic occurrences of the overpressure zones vary across the basin. Three different clusters of wells, covering a large part of the basin encompassing both onshore- and offshore-drilled wells, are analyzed to capture this variation. A wide range of pore-pressure gradients from normal to as high as 18 MPa/km was observed in the present data set. The tops of overpressure zones demonstrate a large range from 2200 to 3000 m (6562 to 9842 ft). These depths generally correspond to either a Miocene deltaic sequence or Cretaceous synrift and postrift sequences. Available well data reveal two main reasons for the development of overpressure. Considerably high pore-pressure regimes in the Cretaceous sequence in the eastern corner of the basin are found to be mainly caused by gas generation, whereas disequilibrium compaction is proposed as the main cause for overpressure in the other parts of the basin. The outcome of this analysis provides a fair idea of the nature, magnitude, and distribution of the overpressure, and this will also help to strategize further exploration activities in the basin.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 7
    Publication Date: 2016-12-16
    Description: Statistical classification methods consisting of the k -nearest neighbor algorithm ( k -NN), a probabilistic clustering procedure (PCP), and a novel method that incorporates outcrop-based thickness criteria through the use of well log indicator flags are evaluated for their ability to distinguish fluvial architectural elements of the upper Mesaverde Group of the Piceance and Uinta Basins as distinct electrofacies classes. Data used in training and testing of the classification methods come from paired cores and well logs consisting of 1626 wireline log curve samples each associated with a known architectural element classification as determined from detailed sedimentologic analysis of cores ( N = 9). Thickness criteria are derived from outcrop-based architectural element measurements of the upper Mesaverde Group. Through an approach that integrates select classifier results with thickness criteria, an overall accuracy (number of correctly predicted samples/total testing samples) of 83.6% was achieved for a four-class fluvial architectural element realization. Architectural elements were predicted with user’s accuracies (accuracy of an individual class) of 0.891, 0.376, 0.735, and 0.985 for the floodplain, crevasse splay, single-story channel body, and multistory channel body classes, respectively. Without the additional refinement by incorporation of thickness criteria, the k -NN and PCP classifiers produced similar results. In both the k -NN and PCP techniques, the combination of gamma ray and bulk density wireline log curves proved to be the most useful assemblage tested.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 8
    Publication Date: 2017-01-16
    Description: The Triassic Yanchang Formation contains the main oil-bearing strata in the Ordos Basin, central China. But the sedimentology of the Upper Triassic is still under debate, and flood-generated, hyperpycnal-flow deposits and their implications for unconventional petroleum development have long been overlooked. Our study indicates that hyperpycnites are well developed in the seventh oil member of the Yanchang Formation. They are characterized by couplets of upward-coarsening intervals and upward-fining intervals, separated by microscale erosion surfaces. The origination of hyperpycnal flows was controlled mainly by episodic tectonic movements and the humid climate. The deposits extend from distributary estuaries into the deep lake, have intercalations of dark shales and tuffs, and coexist with debrites and turbidites as a result of the progradation of subaqueous fans. The hyperpycnites have implications for unconventional petroleum reservoirs, because the flows supplied not only large amounts of coarse grains and organic material to the deep-water, fine-grained central lake sediments but also affected the ecosystems, resulting in a higher total organic carbon content in the sediments.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 9
    Publication Date: 2016-10-18
    Description: In the Qinhuangdao 29 (QHD29) oil field, oil generated from the first member of the Shahejie source rocks is mainly contained in Paleogene reservoirs, whereas deeper oil sourced from the third member of the Shahejie (Es 3 ) source rocks is generally accumulated in Neogene reservoirs. The present study was undertaken to better understand the differences in petroleum accumulation in the QHD29 oil field and to provide suggestions for future petroleum exploration on the Shijiutuo uplift. Laser Raman spectroscopy reveals that carbon dioxide (CO 2 ) exists with hydrocarbon gas in the same fluid inclusions. Measured homogenization temperatures of aqueous inclusions range from 80°C to 160°C (176°F to 320°F), indicating late-stage rapid petroleum accumulation with a charging time of no earlier than 5.1 Ma. The results of grains containing oil inclusions measurements reveal the presence of paleo-oil accumulation in the current natural gas column. In terms of the boundary fault activity rate (FAR), CO 2 distribution is quite relevant to the late-stage activity of boundary faults, with high content of CO 2 corresponding to the section of the F1 fault with high-intensity activity (higher FAR values). Both Neogene and Paleogene reservoirs in well A1 contained predominantly Es 3 -derived oil and were accompanied by abundant mantle CO 2 . This reveals the segmented vertical transport of petroleum in the fault: both the mantle-derived CO 2 and hydrocarbons vertically migrated and accumulated in shallower reservoirs in the high-activity intensity section of the boundary fault. This may account for the occurrence of predominantly Es 3 -derived oil in the reservoirs near the section of the fault with high activity intensity. In the eastern part of the QHD29 oil field, vertical migration may have been limited because of the relatively low intensity of fault activity, and the distribution of sandstones seems to dominate the petroleum accumulation. Our research reveals that lithologic traps in the Es 3 stratum may still have great potential for exploration along the slope of the Shijiutuo uplift.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 10
    Publication Date: 2016-10-18
    Description: Volcanic hydrocarbon reservoirs are rare and may be overlooked. The Carboniferous volcanic rocks of the Kebai fault zone in the western Junggar Basin contain hydrocarbon (HC) reservoirs in volcanic rock with proven oil reserves of 9.76 x 10 8 bbl that have a complex filling history. We have investigated the lithology and properties of these volcanic rock HC reservoirs as well as diagenesis and control of faults and fractures in oil reservoirs. The lithology of these Carboniferous volcanic rocks is primarily andesite and tuff. Also present were volcanic breccia and metamorphic rock in addition to rhyolite, felsite, diabase, and granite in the volcanic lava. On the basis of microscopic examination, five types of pores and fractures were observed: (1) fracture–dissolved phenocrystal pore, (2) fracture–intergranular pore, (3) fracture–gas pore, (4) fracture–dissolved intragranular pore, and (5) fracture–dissolved matrix pore. The fractures in these rocks are a significant factor in connecting the pores. Diagenetic processes that control reservoir quality include compaction, filling of pores and fractures, cementation, metasomatism, and grain dissolution. The volcanic reservoirs show a variety of lithologies, and oil has been discovered in all types of Carboniferous rocks. The controlling factors for oil distribution in these Carboniferous volcanic rocks are faulting, fracture development, and degree of weathering when they were subaerially exposed in the Permian. The area in which these faults and fractures developed is the primary area of oil enrichment with high yields. The objectives of this study were to (1) describe the characteristics of different types of volcanic rocks and reservoirs found in this basin and (2) characterize the diagenetic history of these rocks and document how diagenesis controls porosity and permeability.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 11
    Publication Date: 2016-10-18
    Description: Brine samples were collected from 30 conventional oil wells producing mostly from the Charles Formation of the Madison Group in the East and Northwest Poplar oil fields on the Fort Peck Indian Reservation, Montana. Dissolved concentrations of major ions, trace metals, Sr isotopes, and stable isotopes (oxygen and hydrogen) were analyzed to compare with a brine contaminant that affected groundwater northeast of the town of Poplar. Two groups of brine compositions, designated group I and group II, are identified on the basis of chemistry and 87 Sr/ 86 Sr ratios. The solute chemistry and Sr isotopic composition of group I brines are consistent with long-term residency in Mississippian carbonate rocks, and brines similar to these contaminated the groundwater. Group II brines probably resided in clastic rocks younger than the Mississippian limestones before moving into the Poplar dome to replenish the long-term fluid extraction from the Charles Formation. Collapse of strata at the crest of the Poplar dome resulting from dissolution of Charles salt in the early Paleogene probably developed pathways for the ingress of group II brines from overlying clastic aquifers into the Charles reservoir. Such changes in brine chemistry associated with long-term oil production may be a widespread phenomenon in the Williston Basin.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 12
    Publication Date: 2016-10-18
    Description: The Dabei Gas Field is a recently discovered giant tight-gas field in the Kuqa Subbasin, western China. The reservoir porosity and permeability mainly range from 1% to 8% and from 0.01 to 1 md, respectively. The hydrocarbon (both gas and light oil) accumulation processes in the tight-sandstone reservoirs were studied based on detailed reservoir characterization, thermal maturity of both gas and light oil, hydrocarbon charge history, regional tectonic compression, and thrusting. Two episodes of oil and one episode of natural-gas charge were delineated in the tight-sandstone reservoir, as evidenced by (1) similar sources but different maturities for the gas and light oil, (2) the presence of abundant bitumen in the tight-sandstone reservoir, (3) the presence of both hydrocarbon gas inclusions and oil inclusions with two distinct fluorescence colors, and (4) the presence of two groups of aqueous inclusions (coeval with the petroleum inclusions) with contrasting homogenization temperatures and salinities. The oil inclusions with the blue-white fluorescence color were determined to have been trapped at 5–4 Ma, whereas the gas charge may have occurred at circa 3–2 Ma, corresponding to a salinity change recorded in the aqueous inclusions. The hydrocarbon accumulation processes appeared to be controlled by the tectonic compression of the South Tianshan Mountains. Intense tectonic compression caused thrust fault reactivation, which provided pathways for hydrocarbon migration. Overpressure evolution of the reservoir indicates that an intense tectonic compression began at circa 5 Ma, which caused thrust activation and concomitant oil charge into the relatively porous part of the reservoir. Subsequent tectonic compression caused uplift and erosion associated with thrusting at the end of the Kuqa Formation deposition (ca. 3 Ma), with thrust faults and fractures acting as major migration pathways for the gas accumulation in the already-tight sandstone reservoir resulting from both compaction and tectonic compression.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 13
    Publication Date: 2017-01-16
    Description: Wells in the Piceance Basin show anomalous large-magnitude (up to 200 mV), large-interval (〉2000 ft [610 m]) self-potential (SP) log responses in the Mesaverde gas-producing interval that can be best explained by electrokinetic potential resulting from water flow toward producing Mesaverde wells. Water flow is compartmentalized by capillary seals that are formed when gas generated from coals saturates adjacent thinly bedded sandstones and shales. Capillary seals can be identified by shifts in the SP baseline. The first wells drilled in an area with no previous Mesaverde production have very little SP response, as is expected in tight sandstones with single- to double-digit microdarcy permeability. After Mesaverde production is established in a new area, the SP log begins to show stepwise changes to more negative values beginning in the upper Mesaverde and becoming increasingly more negative with increased depth. The magnitude of the change to more negative values increases with time in an area of active Mesaverde production; some of the more recent SP logs have negative deflections of over 200 mV. This type of SP anomaly has not been reported before, and these anomalies can be used to identify large-scale water movement within a reservoir.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 14
    Publication Date: 2016-10-18
    Description: Karstification positively and negatively affects the quality of carbonate reservoirs; for example, dissolution and brecciation can increase porosity and permeability, whereas cavern collapse or cementation driven by postkarstification fluid flow may occlude porosity and reduce permeability. Karst may also pose challenges to drilling because of the unpredictable and highly variable porosity and permeability structure of the rock and the corresponding difficulty in predicting drilling mud weight. When combined, outcrop, petrographic, and geochemical data can constrain the style, distribution, and origin of seismic-scale karst, which may provide an improved understanding of carbonate reservoir architecture and allow development of safer drilling programs. However, relatively few studies have used seismic reflection data to characterize the regional development of seismic-scale karst features. In this study we use time-migrated two-dimensional seismic reflection data to determine the distribution, scale, and genesis of karst in a 3-km-thick (9800-ft-thick), Jurassic–Miocene carbonate-dominated succession in the Persian Gulf. We map 43 seismic-scale karst features, which are expressed as vertical pipe columns of chaotic reflections capped by downward-deflected depressions that are onlapped by overlying strata. The columns are up to 2 km (6500 ft) tall, spanning the Upper Jurassic to Upper Cretaceous succession, and are up to 5.5 km (18,000 ft) in diameter. We interpret these pipes to have formed in response to hypogene karstification by fluids focused along preexisting faults, with hypogene-generated depressions enhanced by epigene processes during key intervals of exposure. Our study indicates that seismic reflection data can and should be used in conjunction with petrographic and geochemical techniques to determine the presence of hypogene karst plays and to help improve the characterization of carbonate reservoirs and associated drilling hazards.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 15
    Publication Date: 2016-10-18
    Description: Porous siliciclastic reservoirs are known to contain structural heterogeneities such as deformation bands, which fall below current seismic resolution and which generally cannot be explicitly represented in reservoir models because of the prohibitively high computational cost. In this study, we built a reservoir model to evaluate fluid flow across a contractionally folded unit containing deformation bands (the Navajo Sandstone in the San Rafael Reef monocline, Utah). Using field data, geometric relationships, and auxiliary computational techniques, we upscale deformation bands to capture flow effects in the large-scale structure, running simulations with variable scenarios of permeability contrast between host rock and deformation bands. Our simulations show that pervasive deformation band arrays (such as the ones present in the monocline) have effects when the contrast of permeability between them and the host rock is of at least three orders of magnitude, delaying water breakthrough and enhancing sweep; in long-term production, this results in larger final produced volumes and higher total recovery. Because of the wide range of deformation band permeabilities used in this study, our findings can be of importance for the prediction of flow and optimization of production strategies in comparable traps and reservoirs. Additionally, auxiliary computational techniques and geometric relationships such as the ones presented in this study can significantly improve the incorporation of small-scale features with strong scale gap into conventional sized reservoirs.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 16
    Publication Date: 2016-11-16
    Description: The purpose of this paper is to relate diagenetic processes in deeply buried sandstones in the fourth member of the Eocene Shahejie Formation interval, Bohai Bay Basin, China, to pore-fluid flow changes with progressive burial. Based on petrographic, mineralogical, and geochemical analysis, distribution patterns of authigenic minerals are recognized that reflect (1) the sources and patterns of fluid flow and (2) fluid flow in an evolving open-to-closed system. Partial to extensive precipitation of calcite and dolomite at or near mudstone–sandstone contacts during eogenesis was a result of large-scale mass transfer between sandstones and adjacent mudstones. This process was driven by steep diffusion gradients from adjacent mudstones in a relatively open geochemical system on the local scale. Support for this model is provided by large sulfur isotope fractionation between framboidal pyrite and precursor gypsum. Dissolution of feldspar grains and dissolution of nonferroan carbonate cements during early mesogenesis are spatially associated with quartz and ferroan carbonate cementation, respectively. This process was related to organic carbon dioxide expelled from adjacent source rocks and indicates a relatively open system. During late mesogenesis, dissolution of evaporitic cements related to thermochemical sulfate reduction (TSR) generated ankerite and nodular pyrite cements in adjacent pores. A lack of sulfur isotope fractionation between parent anhydrite and late-stage, nodular pyrite during TSR supports a relatively closed fluid-flow system. Because the velocities of pore-fluid flow were low during mesogenesis, large-scale thermal convection and advection probably did not occur. Instead, diffusion over short distances is inferred as the predominant transport mechanism for dissolved solids that were precipitated as other phases either in situ or in adjacent pores.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 17
    facet.materialart.
    Unknown
    American Association of Petroleum Geologists (AAPG)
    Publication Date: 2016-11-16
    Description: Megaflaps are steep stratal panels that extend far up the sides of diapirs or their equivalent welds. They have multiple-kilometer fold widths and structural relief and are thus distinct from smaller-scale composite halokinetic sequences. Maximum dips range from near-vertical to completely overturned. Although overturned megaflaps are associated with flaring salt, there is no direct link between megaflap formation and the initiation of salt sheets. Strata within a megaflap are usually convergent, and the lower boundary is typically concordant with the top salt. The upper boundary ranges between a prominent onlap surface and a more diffuse zone of gradual rotation and thinning, and growth strata likewise display both onlap and stacked wedge geometries. We use quantitative cross-section restoration to elucidate the origin and development of megaflaps. Megaflaps typically represent the relatively thin roofs of early salt structures that include single-flap active diapirs, passive diapirs, salt pillows, and salt sheets. They develop during halokinetic drape folding as the minibasin sinks, during contractional squeezing of the diapir and its roof, or during some combination of the two. The kinematics are dominated by either limb rotation or kink-band migration, in which roof strata move through a fold hinge into a lengthening steep megaflap. Both restoration results and direct field evidence suggest that internal strain is minor, with little bed lengthening and thinning. Recognition and understanding of megaflaps are critical to successful petroleum exploration of three-way truncation traps against salt. Megaflaps also have implications for the lateral seal of stratigraphic traps and fluid pressures in minibasins.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 18
    Publication Date: 2016-11-16
    Description: The morphological evolution of submarine channel systems can be documented using high-resolution three-dimensional seismic data sets. However, these studies provide limited information on the distribution of sedimentary facies within channel fills, channel-scale stacking patterns, or the detailed stratigraphic relationship with adjacent levee-overbank deposits. Seismic-scale outcrops of unit C2 in the Permian Fort Brown Formation, Karoo Basin, South Africa, on two subparallel fold limbs comprise thin-bedded successions, interpreted as external levee deposits, which are adjacent to channel complexes, with constituent channels filled with thick-bedded structureless sandstones, thinner-bedded channel margin facies, and internal levee deposits. Research boreholes intersect all these deposits, to link sedimentary facies and channel stacking patterns identified in core and on image logs and detailed outcrop correlation panels. Key characteristics, including depth of erosion, stacking patterns, and cross-cutting relationships, have been constrained, allowing paleogeographic reconstruction of six channel complexes in a 36-km 2 (14-mi 2 ) area. The system evolved from an early, deeply incised channel complex, through a series of external levee-confined and laterally stepping channel complexes culminating in an aggradational channel complex confined by both internal and external levees. Down-dip divergence of six channel complexes from the same location suggests the presence of a unique example of an exhumed deep-water avulsion node. Down-dip, external levees are supplied by flows that escaped from channel complexes of different ages and spatial positions and are partly confined and share affinities with internal levee successions. The absence of frontal lobes suggests that the channels remained in sand bypass mode immediately after avulsion.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 19
    facet.materialart.
    Unknown
    American Association of Petroleum Geologists (AAPG)
    Publication Date: 2016-12-16
    Description: In contrast to the high-frequency and high-amplitude sea level changes of icehouse times, eustatic sea level changes in greenhouse times are now generally accepted as significantly lower frequency and amplitude. As a corollary of this, frequency and extent of cross-shelf shoreline transits in greenhouse times are also likely to have been modest by comparison, and it has been suggested that greenhouse deltas may have been docked at the shelf edge for long periods, thus delivering sediment to deep-water areas more frequently. A revisit of upper Paleocene–lower Eocene Wilcox data across south Texas shows repeated regressive–transgressive shoreline migrations longer than 50 km (31 mi) at a time scale of some 300 k.y. This style of repeated shoreline transits is documented from well logs and is supported by the repeated presence of transgressive estuarine deposits with strong tidal evidence as interpreted from core. We argue, therefore, that Wilcox paleogeography was more varied than commonly portrayed and that the greenhouse shoreline transits were caused by greenhouse sea level change but severely modulated by variable sediment discharge caused by Paleogene hyperthermals. Periodic climate warming during Wilcox deposition and Laramide relief generation in the drainage areas were also responsible for unusually high sediment flux into the Gulf of Mexico. The factor of sediment supply in shoreline growth and retreat has been understated in the literature, partly because of an overemphasis on accommodation as the main driver of stratigraphic sequences.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 20
    Publication Date: 2016-11-16
    Description: Low-maturity Boquillas Formation (Eagle Ford Formation–equivalent) organic-lean calcareous mudrock samples collected from outcrop were heated in gold tubes under confining pressure to investigate the evolution of organic matter (OM) pores and mineral pores. The majority of OM in the Boquillas samples was migrated petroleum (bitumen) based on evidence from geochemical analyses, solvent extraction, and scanning electron microscopy (SEM) petrography. The SEM images showed several diagenetic events—including framboidal pyrite precipitation and euhedral calcite, quartz, kaolinite, and chlorite cementation—that were all interpreted to have occurred prior to petroleum expulsion and pore-scale to bed-scale petroleum (bitumen) migration. Two major pore types were present prior to heating: primary mineral pores and modified mineral pores with migrated relic OM. From heating experiments, pores were found to be associated with stages of OM maturation. During the bitumen generation stage, modified mineral pores were dominant, and primary interparticle and intraparticle pores were present. During the oil generation stage, modified mineral pores with isopachous OM rim were observed to be the most abundant pore type. During the gas generation stage, both modified mineral pores and nanometer-sized spongy OM pores were predominant. We interpreted the occurrence of modified mineral pores to be the result of (1) oil and gas filled or partially filled voids that developed during petroleum migration and water expulsion; (2) voids after removing of oil, gas, and water during sample preparation; and (3) trapping of water molecules. The formation of these nanopores was interpreted to be related to gas generation and structural rearrangement of OM.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 21
    Publication Date: 2016-11-16
    Description: Paleogene Umm Er Radhuma and Ghaydah and Neogene Sarar source rocks from Sayhut subbasin in the Gulf of Aden Basin were studied to provide information such as organic-matter types, paleoenvironmental conditions, and petroleum-generation potential. This study is based on whole-rock organic-geochemical analyses and organic petrology. The total organic carbon (TOC) contents of the Paleogene to Neogene source rocks range from 0.43% to 6.11%, with an average TOC value of 1.00%, indicating fair to very good source-rock potential. The Paleogene Ghaydah and Umm Er Radhuma source rocks are relatively higher in genetic petroleum potential than Neogene Sarar source rocks. Mainly oil and gas are anticipated from the Ghaydah and Umm Er Radhuma source rocks with hydrogen index (HI) values ranging from 95 to 715 mg hydrocarbon (HC)/g TOC. This is supported by the presence of significant amounts of liptinite macerals in the Ghaydah and Umm Er Radhuma source rocks. The Sarar source rocks are dominated by vitrinitic type III kerogen (HI 〈 200 mg HC/g TOC) and are thus considered to be gas source rocks. The Paleogene to Neogene source rocks have vitrinite reflectance ( R o ) values in the range between 0.30% and 0.77% R o , and pyrolysis maximum temperature values range from 412°C to 444°C (774°F to 831°F), consistent with the immature to early mature oil window. Therefore, the present-day kerogen type in the Paleogene to Neogene source rocks is original and should not have been altered by thermal maturity. The biomarker of organic matter suggests that the Paleogene to Neogene source rocks were deposited in a marine environment under suboxic to anoxic conditions. The biomarkers also indicate that the Paleogene to Neogene source rocks contain a mixture of aquatic organic matter (planktonic and bacterial) and terrigenous organic matter, with increasing terrigenous influence to Sarar source-rock samples. Highly hypersaline reducing conditions are also evidenced in Ghaydah and Umm Er Radhuma source rocks, as indicated by the presence of the gammacerane biomarker, low pristane to phytane ratios, and homohopane distribution patterns.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 22
    facet.materialart.
    Unknown
    American Association of Petroleum Geologists (AAPG)
    Publication Date: 2014-02-03
    Description: Thirty-seven mudstone samples were collected from the uppermost Lower Mudstone Member of the Potrerillos Formation in El Gordo minibasin within La Popa Basin, Mexico. The unit is exposed in a circular pattern at the earth's surface and is intersected by El Gordo diapir in the northeast part of the minibasin. Vitrinite reflectance (R o ) results show that samples along the eastern side of the minibasin (i.e., south of the diapir) are mostly thermally immature to low maturity (R o ranges from 0.53% to 0.64%). Vitrinite values along the southern, western, and northwestern part of the minibasin range between 0.67% and 0.85%. Values of R o immediately northwest of the diapir are the highest, reaching a maximum of 1.44%. The results are consistent with two different possibilities: (1) that the diapir plunges to the northwest, or (2) that a focused high-temperature heat flow existed along just the northwest margin of the diapir. If the plunging diapir interpretation is correct, then the thermally immature area south of the diapir was in a subsalt position, and the high-maturity area northwest of the diapir was in a suprasalt position prior to Tertiary uplift and erosion. If a presumed salt source at depth to the northwest of El Gordo also fed El Papalote diapir, which is located just to the north of El Gordo diapir, then the tabular halokinetic sequences that are found only along the east side of El Papalote may be subsalt features. However, if the diapir is subvertical and the high-maturity values northwest of the diapir are caused by prolonged, high-temperature fluid flow along just the northwestern margin of the diapir, then both of these scenarios are in disagreement with previously published numerical models. This disagreement arises because the models predict that thermal anomalies will extend outward from a diapir a distance roughly 1.5 times the radius of the diapir, but the results reported here show that the anomalous values on one side of the diapir are about two times the radius, whereas they are as much as five times the radius on the other side of the diapir. The results indicate that strata adjacent to salt margins may experience significantly different heat histories adjacent to different margins of diapirs that result in strikingly different diagenetic histories, even at the same depth.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 23
    Publication Date: 2014-02-03
    Description: The Molasse Basin represents the northern foreland basin of the Alps. After decades of exploration, it is considered to be mature in terms of hydrocarbon exploration. However, geological evolution and hydrocarbon potential of its imbricated southernmost part (Molasse fold and thrust belt) are still poorly understood. In this study, structural and petroleum systems models are integrated to explore the hydrocarbon potential of the Perwang imbricates in the western part of the Austrian Molasse Basin. The structural model shows that total tectonic shortening in the modeled north–south section is at least 32.3 km (20.1 mi) and provides a realistic input for the petroleum systems model. Formation temperatures show present-day heat flows decreasing toward the south from 60 to 41 mW/m 2 . Maturity data indicate very low paleoheat flows decreasing southward from 43 to 28 mW/m 2 . The higher present-day heat flow probably indicates an increase in heat flow during the Pliocene and Pleistocene. Apart from oil generated below the imbricated zone and captured in autochthonous Molasse rocks in the foreland area, oil stains in the Perwang imbricates and oil-source rock correlations argue for a second migration system based on hydrocarbon generation inside the imbricates. This assumption is supported by the models presented in this study. However, the model-derived low transformation ratios (〈20%) indicate a charge risk. In addition, the success for future exploration strongly depends on the existence of migration conduits along the thrust planes during charge and on potential traps retaining their integrity during recent basin uplift.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 24
    facet.materialart.
    Unknown
    American Association of Petroleum Geologists (AAPG)
    Publication Date: 2014-02-03
    Description: Sandstone pressures follow the hydrostatic gradient in Miocene strata of the Mad Dog field, deep-water Gulf of Mexico, whereas pore pressures in the adjacent mudstones track a trend from well to well that can be approximated by the total vertical stress gradient. The sandstone pressures within these strata are everywhere less than the bounding mudstone pore pressures, and the difference between them is proportional to the total vertical stress. The mudstone pressure is predicted from its porosity with an exponential porosity-versus-vertical effective stress relationship, where porosity is interpreted from wireline velocity. Sonic velocities in mudstones bounding the regional sandstones fall within a narrow range throughout the field from which we interpret their vertical effective stresses can be approximated as constant. We show how to predict sandstone and mudstone pore pressure in any offset well at Mad Dog given knowledge of the local total vertical stress. At Mad Dog, the approach is complicated by the extraordinary lateral changes in total vertical stress that are caused by changing bathymetry and the presence or absence of salt. A similar approach can be used in other subsalt fields. We suggest that pore pressures within mudstones can be systematically different from those of the nearby sandstones, and that this difference can be predicted. Well programs must ensure that the borehole pressure is not too low, which results in borehole closure in the mudstone intervals, and not too high, which can result in lost circulation to the reservoir intervals.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 25
    Publication Date: 2016-07-16
    Description: Modeling of fluid flow in naturally fractured reservoirs is often done through modeling and upscaling of discrete fracture networks (DFNs). The two-dimensional fracture geometry required for DFNs is obtained from subsurface and outcropping analog data. However, these data provide little information on subsurface fracture aperture, which is essential for quantifying porosity and permeability. Apertures are difficult to obtain from either outcropping or subsurface data and are therefore often based on fracture size or scaling relationships, but these do not consider the orientation and spatial distribution of fractures with respect to the in situ stress field. Using finite-element simulations, mechanical aperture can be modeled explicitly, but because changes in fracture geometry require renewed meshing and simulating, this approach is not easily integrated into subsurface DFN modeling workflows. We present a geometrically based method for calculating the shear-induced hydraulic aperture, that is, an aperture of up to 0.5 mm (0.02 in.) that can result from shear displacement along irregular fracture walls. The geometrically based method does not require numerical simulations, but it can instead be directly applied to DFNs using the fracture orientation and spacing distributions in combination with an estimate of the regional stress tensor and orientation. The frequency distribution of hydraulic aperture from the geometrically based method is compared with finite-element models constructed from five real fracture networks, digitized from outcropping pavements. These networks cover a wide range of possible geometries and spatial distributions. The geometrically based method predicts the average hydraulic aperture and equivalent permeability of fractured porous media with error margins of less than 5%.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 26
    Publication Date: 2016-07-16
    Description: The Lower Cretaceous presalt section in the Kwanza Basin contains an excellent petroleum system that includes "synrift" strata (Barremian) overlain by a "sag" interval (Aptian) and capped by the Loeme Salt. The upper synrift is generally limestone with widespread mollusk packstones and grainstones (coquinas) deposited in a fresh-to–moderately saline (alkaline) lake. The sag interval is characterized by carbonate platforms and silica-rich isolated buildups formed in highly evaporated, highly alkaline lakes. Shrubby (dendritic), microbially influenced boundstones and intraclast–spherulite grainstones accumulated in shallow water on platform tops. Microbial cherts were deposited as organic buildups on large, isolated structural highs basinward (west) of platforms, and they apparently formed at low temperatures in very alkaline lake water. Shrubby boundstones and microbial cherts have vuggy pores that are primary and result in high permeability. Wackestones and packstones with calcitic grains (mainly spherulites) in dolomite or argillaceous dolomite were deposited in slightly deeper, low-energy sag environments. In addition, clays (especially stevensite) precipitated out of the silica-rich, highly alkaline lake waters. During sag deposition, calcite precipitated on the shallow lake floor with morphologies that ranged from spherulites to shrubs and included a continuum of intermediate forms. Spherulites probably precipitated just below the sediment–water interface. Spherulites and shrubby calcites are commonly recrystallized. Spherulites floating in stevensite probably formed in deeper lacustrine environments. Organic-rich mudstones were deposited in even deeper lacustrine environments in synrift and sag intervals, and they are likely the source of most hydrocarbons in this system. These interpretations are supported by seismic, core, petrographic, and stable isotope data.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 27
    Publication Date: 2016-06-16
    Description: Huge, high gas–oil ratio, hydrogen sulfide (H 2 S)-bearing gas condensate accumulations were recently discovered in the Ordovician carbonate reservoirs of the Tazhong uplift in the Tarim Basin, northwest China. Distinct differences exist between the eastern and western condensates in terms of chemical and isotopic compositions. Condensates from the western part of the uplift were characterized by high dibenzothiophenes (generally 〉500 μg/g), a high H 2 S concentration (~7%, vol./vol.), and relatively depleted 13 C methane ( 13 C 1 = –55.5 to –36). The H 2 S concentration in the Tazhong gas condensates shows a positive correlation to Mg 2+ concentration in the formation water. Formation water in Lower Ordovician–Cambrian strata in the Tazhong uplift is rich in Mg 2+ , which facilitates the thermochemical sulfate reduction (TSR) of sulfate contact ion pairs (CIPs) to produce H 2 S and dibenzothiophenes. A detailed comparison of the chemical compositions of the formation waters in different strata indicates that a high H 2 S concentration in the Tazhong gas condensates originates from the TSR of sulfate CIPs in the Lower Ordovician–Cambrian strata, where a primary oil accumulation may have existed. The concentrations of 3- and 4-methyldiamantanes in the western condensates (80 to 150 μg/g) are relatively lower than those from the eastern part of the uplift. Also, the 13 C 1 in the western H 2 S-bearing gas condensates was more negative, and the 13 C 2 – 13 C 1 value was larger than that from typical TSR-altered gases. These features indicate that the western Tazhong samples had just entered the initial stage of TSR. According to the pressure, volume, temperature (PVT) phase diagram, the lower Paleozoic section was quickly buried after the Tortonian. High-H 2 S hydrocarbon inclusions formed during the last 10 m.y. when paleotemperatures reached 140°C (284°F). Because the reaction rate of the sulfate CIPs oxidation was relatively slower than that of H 2 S autocatalysis during the entire TSR process, advanced TSR has not been accomplished yet. It is also inferred that the Tortonian was the key period for accumulation of secondary H 2 S-bearing gas condensates, resulting from abundant gas washing along deep fractures and charging in the early reservoirs. An increased aromaticity parameter (toluene/n-heptane) and an increased fractionation index from east to west indicate an intensified degree of gas washing. Different gas-washing intensities in the eastern and western gas condensates led to diverse PVT states as well. Deep strata in the Tazhong uplift were characterized by multiple charges and mixing, coupled with periodic TSR, leading to the occurrence of variable H 2 S-bearing gas condensates.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 28
    Publication Date: 2016-06-16
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 29
    Publication Date: 2016-06-16
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 30
    Publication Date: 2016-06-16
    Description: The Bohai Sea area, offshore of the Bohai Bay Basin, is one of the most petroliferous regions in China, with proven original oil in place of approximately 2.4 x 10 9 m 3 (150.94 x 10 8 bbl) and proven original gas in place of over 5 x 10 12 m 3 (1.76 x 10 13 ft 3 ). Cumulative oil production is over 50 million tons (3.5 x 10 8 bbl). In this study, using the limited data on source rock thickness, core samples, and Rock-Eval pyrolysis along with sedimentary facies analysis, source rock characteristics of different depositional settings were identified, and the thickness, richness, organic matter type, and thermal evolution of four sets of source rocks in the Bohai Sea area— the second member of Dongying Formation (E 3 d 2 ), the third member of Dongying Formation (E 3 d 3 ), the first and second members of Shahejie Formation (E 2 s 1-2 ), and the third member of Shahejie Formation (E 2 s 3 )—were predicted and evaluated. Subsequently, the intensity and history of hydrocarbon expulsion for different sags was systematically compared and analyzed. The greatest thickness of the four sets of source rocks in the Bohai Sea area is 400–800 m (1300–2600 ft). The average richness of the organic matter of these source rocks is 1.74%–2.87%. The E 2 s 3 set has the highest organic matter abundance; E 2 s 1-2 has the lowest. The organic matter of these source rocks is mainly type I and type II, but their evolutions differ. The vitrinite reflectance of E 3 d 2 is 0.5%–1.0%, that of E 3 d 3 is 0.7%–1.25%, that of E 2 s 1-2 is 0.75%–1.75%, and that of E 2 s 3 is 0.75%–2.0%. The cumulative hydrocarbon expulsion of the four sets of rocks is 4.14 x 10 10 t (2.90 x 10 11 bbl). The E 2 s 1-2 set has the greatest expulsion amount: 1.75 x 10 10 t (1.22 x 10 11 bbl). The peak stages of hydrocarbon expulsion of the four sets of source rocks were during Neogene Minghuazhen Formation (12.2–2.0 Ma) and Neogene Guantao Formation (16.6–12.0 Ma). The Bozhong sag expelled the most hydrocarbons, followed by the Liaozhong, Qikou, and Huanghekou sags.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 31
    Publication Date: 2016-06-16
    Description: Oxygen isotope ( 18 O) zonation in carbonate mineral cements is often employed as a proxy record (typically with millimeter-scale resolution) of changing temperature regimes during different stages of sediment diagenesis. Recent advances in secondary ion mass spectrometry allow for highly precise and accurate determinations of cement 18 O values to be made in situ on a micrometer scale, thus significantly increasing the spatial resolution available to studies of diagenesis in sandstone–shale and carbonate systems. Chemo-isotopically zoned dolomite–ankerite cements within shaly sandstone beds of the predominantly silty–shaly Eau Claire Formation (Cambrian, Illinois Basin) were investigated, revealing the following: with increasing depth of burial (from 〈0.5 to ~2 km [〈1500 to 6500 ft]), cement 18 O values decrease from a high of approximately 24 down to approximately 14 (on the Vienna standard mean ocean water [VSMOW] scale, equivalent to –6.5 to –16.5 on the Vienna Peedee belemnite [VPDB] scale). The observed cross-basin trend is largely consistent with cements having formed in response to progressive sediment burial and heating. Within the context of independent burial and thermal history models for the Illinois Basin, cementation began soon after deposition and continued intermittently into the mid-Permian. However, temperatures in excess of burial model predictions are inferred at the time of latest ankerite cement precipitation, which we propose overlapped in time with conductive heating of the Eau Claire Formation (a closed system) from under- and overlying sandstone aquifers that channeled the flow of hot, Mississippi Valley–type mineralizing brines during the mid-Permian (ca. 270 Ma).
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 32
    Publication Date: 2016-04-21
    Description: In this paper we use three-dimensional seismic attribute imaging and well data to reveal the previously unknown quantitative measures, directionality, and spatial locations of the Oligocene middle Frio fluvial channel systems within an area of 254 km 2 (98 mi 2 ) that covers two oil and gas fields in the Texas Gulf Coast Basin of the United States. The objective of this study is to apply quantitative seismic geomorphology techniques to quantify the morphometric parameters important to building predictive geologic models for fluvial reservoirs. Three categories of channel systems are differentiated based on their geomorphology, seismic signature, and the mode of transport. The first, category 1, includes channel systems of high-amplitude, moderate- to high-sinuosity, mixed load channels. Category 2 channel systems are high-amplitude, straight to low-sinuosity, bed load channels with both category 1 and 2 channels filled with coarse-grained sandstone deposits. Category 3 crevasse channel systems are low-amplitude, highly sinuous, suspended load channels filled with fine-grained deposits. These fluvial system categories were found to show unique morphometric characteristics such as channel width, meander belt width, and meander length. Analysis of the middle Frio channel systems imaged in the south Texas study area revealed a significant downstream decrease of channel belt width along the length of the channel belts. The creation of a quantitative morphometric database for the middle Frio fluvial reservoirs in the basin would be very useful for exploration and development purposes. The results of this study may have general applicability to the Texas Gulf Coast Basin and to similar fluvial reservoirs worldwide.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 33
    Publication Date: 2016-04-21
    Description: The role of deep-burial dissolution in the creation of porosity in carbonates has been discussed controversially in the recent past. We present a case study from the Upper Permian Zechstein 2 carbonate reservoirs of the Lower Saxony Basin in northwest Germany. These reservoirs are locally characterized by high amounts of carbon dioxide (CO 2 ) and variable amounts of hydrogen sulfide (H 2 S), which are derived from thermochemical sulfate reduction (TSR) and inorganic sources. To study the contribution of these effects on porosity development, we combine petrography, stable isotope, and rare earth and yttrium (REY) analyses of fracture cements with Raman spectroscopy and 13 C analyses of fluid inclusions. It is shown that fluid migration along deep fault zones created and redistributed porosity. Fluid inclusion analyses of vein cements demonstrate that hydrothermal fluids transported inorganic CO 2 into the reservoir, where it mixed with minor amounts of TSR-derived organic CO 2 . The likely source of inorganic CO 2 is the thermal decomposition of deeply buried Devonian carbonates. The REY distribution patterns support a hydrothermal origin of ascending iron- and CO 2 -rich fluids causing dolomitization of calcite and increasing porosity by 10%–16% along fractures. This porosity increase results from hydrothermal dolomitization and dissolution by acids generated from the reaction of Fe 2+ with H 2 S to precipitate pyrite. In contrast, hydrothermal dolomite cements reduced early diagenetic porosity in dolomitic intervals by approximately 17%. However, the carbonate dissolution in the predominantly calcitic host rock results in a net increase in porosity and permeability in the vicinity of the fracture walls, which has to be considered for modeling reservoir properties and fluid migration pathways.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 34
    Publication Date: 2016-04-21
    Description: A detailed sedimentological study of the middle Eagle Ford/Boquillas (outcrop analog of subsurface producing strata) units was conducted on numerous roads cut along US Highway 90 in Val Verde County and on outcrops in Big Bend National Park, Brewster County, Texas, using field-based petrographical and high-resolution image capture methods (light detection and ranging and GigaPans). This study demonstrates that vertical and lateral facies distribution is controlled by the interaction of sediment productivity under the influence of bottom currents below storm wave base. Vertical cyclicity is the result of alternating periods of lower primary productivity and relatively low sediment accumulation rates (globigerinid argillaceous wackestones) and shorter periods of high primary productivity and higher accumulation rates (pelagic grainstones), driven by the absence or presence of iron from volcanic ash deposition. Lateral variations are controlled by the deposition and reworking of pelagic sediment under the influence of below–storm wave base bottom currents. Pelagic grainstones accumulated in the form of isolated barchanoid hydraulic dunes, sand ridges, coalesced sand ridges, and sand sheets and less commonly as continuous beds. Detailed measurements show that pelagic grainstones have no more than 50% continuity, and ash beds have 72% continuity. Application of sequence stratigraphic principles needs to be done with caution because the deeper-water depositional setting is affected not by sediment input from a shallow-water benthic carbonate factory but by pelagic sediment from the open-marine environment subject to bottom current reworking. Packages of strata may be more reliable for longer-distance correlations.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 35
    Publication Date: 2016-05-19
    Description: Hydrocarbons have recently been discovered in Upper Triassic to Middle Jurassic siliciclastic reservoirs in the Rub' Al-Khali basin in Saudi Arabia. The reservoirs fill accommodation space created by Triassic and early Jurassic crustal-scale basins on the order of 100 km (62 mi) in wavelength and hundreds of meters in depth. These basins are separated by highs that are interpreted as crustal-scale epeirogenic folds. Lithologies include well-sorted quartz arenites deposited in shallow-marine, shoreface, and fluviodeltaic settings. These sequences can be correlated across the basin to extensive escarpment outcrops south of Riyadh and beyond Saudi Arabia into well-documented equivalents elsewhere in the Middle East and East Africa. The gross architecture of the interval is imaged on reflection seismic, showing clinoformal geometries and onlap onto the Triassic structured surface. Geochemistry of tested fluids indicates a type III kerogen source. The simplest interpretation is that the system is self-sourcing hydrocarbons from interbedded coaly material that is observed in the wells and at outcrop. Reservoir pressures are anomalously low relative to the overlying carbonate reservoir systems. These low pressures are interpreted to indicate lateral communication from the Rub' Al-Khali basin westward to outcrop, in contrast with the overlying carbonate fairways that are known to contain facies boundaries that trend across the regional dip. Onlapping geometries in the siliciclastic fairway combine with Cretaceous and Cenozoic compressional structures to create combined structural-stratigraphic traps.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 36
    Publication Date: 2016-05-19
    Description: Conduit fault zones and fault zones that can accommodate long-distance along-fault flow are well-documented phenomena. In reservoir simulation models, flow within these features is more correctly captured using volumetric representations of fault zones instead of employing standard two-dimensional fault planes. The present study demonstrates a method for generating fault envelope grids on full-field reservoir models, within which fault cores (i.e., regions where most of fault zone displacement is accommodated) are modeled. The modeled fault core elements are lenses and slip zones. They are defined as facies units and populated in the fault envelope grids using combined object-based simulation and deterministic techniques. Using the facies property, four reservoir simulation models are generated by modulating fault core thickness and slip zone type and permeability. Membrane slip zones (slip zones that act as partial barriers to fluid flow) cause the fault cores to form baffle–conduit systems. Along-strike positioned injector–producer pairs focus flow into the fault cores, decreasing sweep efficiency. In contrast, injected fluids of injector–producer pairs positioned to drain perpendicular to the fault cores are partitioned and distributed by the fault cores and therefore increase overall sweep efficiency. In reservoir models with conduit slip zones (slip zones that enhance flow along them and act as partial barriers to flow across them), the fault cores act as thief zones. Fluids preferentially move through the fault cores toward the nearby producers instead of through sedimentary layers with high permeability. Sweep efficiency in the reservoir models with conduit fault cores has less dependency on injector–producer configuration. Our study suggests that the improved realism added by incorporating volumetrically expressed fault cores substantially influences forecasts of field behavior and consequently should be considered during oil and gas production planning.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 37
    Publication Date: 2016-05-19
    Description: The Vaca Muerta–Quintuco system (uppermost lower Tithonian–lower Valanginian) is a thick shallowing-upward sedimentary cycle consisting of dark bituminous shales, marlstones, limestones, and sandstones, cropping out in the Neuquén Basin, west–central Argentina. This paper analyzes three outcrop sections in Chos Malal area, northem Neuquén province. Detailed facies analysis allows us to differentiate six facies associations, representing basinal to proximal outer ramp facies of a homoclinal carbonate ramp system (Vaca Muerta Formation) and basinal to shoreface facies of a mixed carbonate–siliciclastic shelf system (Quintuco Formation), prograding westward from the eastern margin of the basin. Two sequence hierarchies were recognized: 5 composite depositional sequences (third order) and 15 high-frequency sequences (fourth order). Fluctuations in organic matter content within the Vaca Muerta Formation suggest a relationship with depositional sequences, finding the highest values associated with transgressive systems tract, whereas the transition to the Quintuco Formation shows a strong decrease in total organic carbon. The x-ray diffraction studies show an increase of clay minerals and quartz in the transgressive systems tract of the Vaca Muerta Formation and an increase in the content of calcite in highstand systems tracts. This pattern is reversed in the Quintuco Formation. Our sequence stratigraphic approach contributes to the understanding of the relationship between organic matter, clay minerals, facies, stacking pattern, and relative sea level changes in this exceptional shale oil and shale gas unconventional reservoir. This study may be helpful for a better postulate of petrophysical and geomechanical models for unconventional exploration.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 38
    Publication Date: 2016-05-19
    Description: Tidal heterolithic sandstones are commonly characterized by millimeter- to centimeter-scale intercalations of mudstone and sandstone. Consequently, their effective flow properties are poorly predicted by (1) data that do not sample a representative volume or (2) models that fail to capture the complex three-dimensional architecture of sandstone and mudstone layers. We present a modeling approach in which surfaces are used to represent all geologic heterogeneities that control the spatial distribution of reservoir rock properties (surface-based modeling). The workflow uses template surfaces to represent heterogeneities classified by geometry instead of length scale. The topology of the template surfaces is described mathematically by a small number of geometric input parameters, and models are constructed stochastically. The methodology has been applied to generate generic, three-dimensional minimodels (9 m 3 [~318 ft 3 ] volume) of cross-bedded heterolithic sandstones representing trough and tabular cross bedding with differing proportions of sandstone and mudstone, using conditioning data from two outcrop analogs from a tide-dominated deltaic deposit. The minimodels capture the cross-stratified architectures observed in outcrop and are suitable for flow simulation, allowing computation of effective permeability values for use in larger-scale models. We show that mudstone drapes in cross-bedded heterolithic sandstones significantly reduce effective permeability and also impart permeability anisotropy in the horizontal as well as vertical flow directions. The workflow can be used with subsurface data, supplemented by outcrop analog observations, to generate effective permeability values to be derived for use in larger-scale reservoir models. The methodology could be applied to the characterization and modeling of heterogeneities in other types of sandstone reservoirs.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 39
    Publication Date: 2016-05-19
    Description: The purpose of this work was to study the depositional mechanisms and significance of the Longmaxi shale in the Sichuan Basin in southern China. Seven lithofacies were identified based on the detailed observation of outcrops and cores using petrographic and scanning electron microscope examination of thin sections and other data analyses: (1) laminated calcareous mudstone, (2) laminated carbonaceous mudstone, (3) laminated silty mudstone, (4) laminated claystone, (5) laminated siliceous shale, (6) siltstone, and (7) massive mudstone. The laminated mudstone and laminated claystone originated from suspension deposition, and siliceous shale is associated with ocean upwelling, whereas massive mudstone and siltstone were primarily deposited by turbidity currents. The depositional mechanisms have a great effect on the source rock and reservoir properties. Suspension deposition near oceanic upwelling zones can provide favorable conditions for the production and preservation of organic matter and are thus conducive to the formation of high-quality source rocks (total organic carbon content up to 5.4%). The reservoir storage spaces are primarily interlaminated fractures and organic pores with good physical reservoir properties (high porosity, permeability, and brittle mineral content). Turbidity currents may carry a large quantity of oxygen to the seafloor, resulting in the oxidation of organic matter, which is unfavorable for its preservation. The lithofacies formed by turbidity currents have relatively low total organic carbon contents (average: 〈1%). Structural fractures and intergranular pores are the primary storage spaces that are present in the reservoir. In summary, organic-rich shale and siliceous shale that was deposited from suspension near upwelling zones are key exploration targets for shale oil and gas. The widely distributed, multilayer, tight sandstone is important in the exploration for tight oil. A better understanding of the deposition mechanism and its effect on oil reservoirs may assist in identification of favorable areas for exploration.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 40
    Publication Date: 2016-05-19
    Description: Tidal heterolithic sandstone reservoirs are heterogeneous at the submeter scale because of the ubiquitous presence of intercalated sandstone and mudstone laminae. Core-plug permeability measurements fail to sample a representative volume of this heterogeneity. Here, we investigate the impact of mudstone drape distribution on the effective permeability of heterolithic, cross-bedded tidal sandstones using three-dimensional, surface-based "minimodels" that capture the geometry of cross beds at an appropriate scale. The impact of seven geometric parameters has been determined: (1) mudstone fraction, (2) sandstone laminae thickness, (3) mudstone drape continuity, (4) toeset dip, (5) climb angle of foreset–toeset surfaces, (6) proportion of foresets to toesets, and (7) trough or tabular geometry of the cross beds. We begin by identifying a representative elementary volume of 1 m 3 (~35 ft 3 ), confirming that the model volume of 9 m 3 (~318 ft 3 ) yields representative permeability values. Effective permeability decreases as the mudstone fraction increases, and it is highly anisotropic: vertical permeability falls to approximately 0.5% of the sandstone permeability at a mudstone fraction of 25%, whereas the horizontal permeability falls to approximately 5% and approximately 50% of the sandstone value in the dip (across mudstone drapes) and strike (parallel to mudstone drapes) directions, respectively. Considerable spread exists around these values, because each parameter investigated can significantly impact effective permeability, with the impact depending upon the flow direction and mudstone fraction. The results yield improved estimates of effective permeability in heterolithic, cross-bedded sandstones, which can be used to populate reservoir-scale model grid blocks using estimates of mudstone fraction and geometrical parameters obtained from core and outcrop-analog data.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 41
    Publication Date: 2016-05-19
    Description: The Sichuan Basin is a prime gas-producing basin in China. Besides the giant Neoproterozoic Weiyuan gas field discovered in the central paleo-uplift, an extra giant gas reservoir in the Cambrian in this area has been confirmed in recent years. Although the lower Paleozoic in the southwest (Weiyuan area) is normally pressured, it is overpressured in the central area (Moxi–Gaoshiti area). Combined with the seal distribution, five pressure systems, including three overpressure systems, can be divided based on drill-stem test, mud weight, and sonic transit time data. Overpressures appear at depth interval of 1500 to 4900 m (4921 to 16,076 ft), approximately. Benefiting from the good sealing capacity of the gypsum in the Upper and Middle Triassic, high overpressure (pressure coefficient [ r ] 〉 2.0) has been preserved in the Lower Triassic, and the Upper Triassic and Cambrian are moderately overpressured (1.3 〈 r 〈 1.7). Mechanisms for various overpressure systems are different. Abnormally high sonic transit time in the Permian indicates disequilibrium compaction overpressure. The analyses of sonic transit time–effective stress suggest that disequilibrium compaction is the primary mechanism for the overpressure in the Upper Triassic Xujiahe Formation, but the Cambrian overpressure system is predominantly associated with fluid expansion, which mainly resulted from gas generation. Furthermore, we consider that the late thermal cracking of oil to gas is a key factor for gas and overpressure preservation in old strata. The high overpressure in the Lower Triassic marine carbonate rocks was caused by oil cracking and gypsum dehydration mechanisms. Combining the origin analysis with the burial and hydrocarbon generation histories, we constructed the Cambrian pore pressure evolution model, which is characterized by roughly normal pressure before 200 Ma, overpressuring from 200 to 90 Ma, and overpressure releasing since 90 Ma.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 42
    Publication Date: 2016-05-19
    Description: A novel hydrogeochemical modeling approach is developed to unravel thermochemical sulfate reduction (TSR) in hydrocarbon reservoirs. Our numerical model couples a web of interconnected hydrogeochemical reactions to three-dimensional (3-D) and reservoir-wide diffusive mass transport. Our modeling approach simulates a semigeneric gas reservoir sealed by anhydrite. The calculated diagenetic processes fit the observations in reservoirs affected by TSR: formation of water, precipitation of calcite, metal (di-)sulfides, and elemental sulfur as replacements of dissolved anhydrite at the expense of CH 4(g) , as well as formation of hydrogen sulfide (H 2 S). By varying input parameters, the crucial factors controlling TSR have been identified. Our results highlight that reservoir-wide diffusive mass transport is one prerequisite for TSR. An increase in the rate constant of abiotic sulfate reduction (ASR) and in diffusive mass fluxes, as well as lack of precursor minerals for metal (di-)sulfide precipitation, can increase the souring intensity and accelerate H 2 S outgassing. In contrast, precipitation of elemental sulfur, which is stable according to the chemical thermodynamics, weakens H 2 S formation. Our modeling shows that TSR is complex and cannot be represented by the single reaction ASR and by simple correlations between the rate constant of ASR and the H 2 S gas content. The application of 3-D reactive transport modeling presented here, despite its semigeneric nature, provides a good example of how such an approach can be used ahead of drilling. Our modeling helps to investigate TSR in time and space to quantify the mass conversion of all reactants involved within this web and to predict the souring level.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 43
    Publication Date: 2016-06-16
    Description: Geochemical fingerprinting of produced water from hydraulic fracturing projects is an essential tool to trace their provenance during the postfracturing period, to quantify recovery rates and volumes of fracturing fluids, and to visualize the geodynamic structure of natural or induced fracture networks. A total of 41 produced water samples from an exploration well in the Northern Arabia Exploration Area in Saudi Arabia were collected daily from the fracture-stimulated Qusaiba hot shale and analyzed for major ions and trace elements and partially for environmental isotopes. The postfracturing period shows an initial return of supply water and potassium chloride brine, subsequently replaced by the inflow of sodium chloride–type formation water with a stable plateau salinity of 50,000 mg/L. Less than 10% of the total injected fracturing fluids were recovered during postfracturing, whereas 78.8 vol. % of the total recovered fluid is composed of formation water (20,843 out of 26,446 bbls) during the study period. Coinciding values between logged reservoir temperature and calculated geothermometers confirm the provenance of pore water from the Qusaiba hot shale or from nearby units. The recharge of the Silurian sequence with meteoric surface water occurred during the early Holocene (6–6.7 ka), as evidenced by geochronological dating with the 14 C method and 18 O/ 2 H values close to the global meteoric water line. The inflow of formation water into the stimulated shale layer in the postfracturing stage could be originated by the natural occurrence of pore water within a naturally fractured, black shale layer or, more likely, by the rise of groundwater from the underlying Sarah sandstones via migration pathways of natural or newly formed, vertically induced hydraulic fractures. For this particular well site and the specific hydraulic fracturing project, chemical and isotopic fingerprinting confirms the absence of ascending migration pathways from the Silurian Qusaiba hot shale toward a shallower groundwater system, which are isolated through a lithological set of more than 900 m (3000 ft) of impermeable mudstone from the Qusaiba Member.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 44
    facet.materialart.
    Unknown
    American Association of Petroleum Geologists (AAPG)
    Publication Date: 2016-07-16
    Description: The natural fracture system developed in the Cardium sandstone is examined in four outcropping structures that represent different stages of fold development. At the incipient stage of folding, the fracture system is dominated by large, widely spaced hybrid fractures that have very small displacements and are aligned in the regional shortening direction (type I orientation). These fractures are naturally propped open by asperities along the fracture surfaces. A lesser number of small thrust faults (type III orientation) are also developed. Extension fractures aligned parallel to the fold axis (type II orientation) begin to develop in the early stage of folding. Through the intermediate stage of folding, there is a progressive increase in the intensity of both type I and type II orientation fractures. Incremental increases in shear displacement on new or reactivated fractures create a gouge of comminuted sandstone grains along the fracture interface. As folding progresses to an advanced stage, there is major increase in the amount of shear displacement on both type I and type II orientation fractures. Many existing fractures coalesce into connected fracture zones and small faults that have shear offsets ranging from several centimeters to several meters. A breccia can result from intense fracturing in the rock within and marginal to these shear features. Slickensides on type I orientation features consistently indicate slip in a subhorizontal direction, even as bed dip increases. Multiple slickenside patterns record reactivation of these features. Type II orientation fractures and small faults consistently undergo bed-perpendicular slip. Type I and type II features both serve to stretch the Cardium sandstone beds but in different directions. Only type III features, which are a minor component of the fracture population, result in bed thickening.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 45
    Publication Date: 2016-07-21
    Description: Substrate relief is a common characteristic of hard-bottom offshore banks and is associated with benthic biodiversity. Earlier studies revealed varying relief associated with offshore mesophotic communities. Correlations may exist between relief and benthic biodiversity, which in turn may be useful in determining drill sites. Such drill site determination requires obtaining an estimate of variability in relief on these banks and its associated geographic patterns. We performed fine-scale surveys of relief on 14 banks in the Gulf of Mexico to examine variation between them, geographic patterns, and possible processes influencing them: 28 Fathom, 29 Fathom, Alderdice, Bouma, Bright, Elvers, Geyer, Horseshoe, McGrail, Parker, Rankin, Rezak, Sidner, and Sonnier Banks. We used a multibeam sensor on a remotely operated vehicle, with resolution of approximately 0.5 m (2 ft). Average and standard deviation of relief were calculated at the transect, drop site, and bank levels of resolution. Sidner and McGrail Banks had the highest relief, and 29 Fathom and Sonnier had the lowest. Sidner Bank had relief averaging up to 11 m (36 ft) in height, whereas 29 Fathom Bank exhibited the lowest relief (range 1 to 2 m [3 to 7 ft]). Bright Bank and all others exhibited intermediate and variable relief at both the transect and drop site levels. Relief is not predictable on many banks because of high variability between drop sites. Some low-relief banks are predictable in their relief, lending themselves to predictions of benthic diversity and suitable drill sites. Relief decreased significantly as one moved northward in the study region. Relief exhibited a significant sinusoidal pattern from west to east. Banks with low relief occurred off Lake Calcasieu and Lafayette, Louisiana.
    Print ISSN: 1075-9565
    Electronic ISSN: 1526-0984
    Topics: Geography , Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 46
    Publication Date: 2016-07-21
    Description: Numerical geochemical modeling was used to study the effects on pore-water composition and mineralogy from carbon dioxide (CO 2 ) injection into the Pennsylvanian Morrow B Sandstone in the Farnsworth Unit in northern Texas to evaluate its potential for long-term CO 2 sequestration. Speciation modeling showed the present Morrow B formation water to be supersaturated with respect to an assemblage of zeolite, clay, carbonate, mica, and aluminum hydroxide minerals and quartz. The principal accessory minerals in the Morrow B, feldspars and chlorite, were predicted to dissolve. A reaction-path model in which CO 2 was progressively added up to its solubility limit into the Morrow B formation water showed a decrease in pH from its initial value of 7 to approximately 4.1 to 4.2, accompanied by the precipitation of small amounts of quartz, diaspore, and witherite. As the resultant CO 2 -charged fluid reacted with more of the Morrow B mineral matrix, the model predicted a rise in pH, reaching a maximum of 5.1 to 5.2 at a water–rock ratio of 10:1. At a higher water–rock ratio of 100:1, the pH rose to only 4.6 to 4.7. Diaspore, quartz, and nontronite precipitated consistently regardless of the water–rock ratio, but the carbonate minerals siderite, witherite, dolomite, and calcite precipitated at higher pH values only. As a result, CO 2 sequestration by mineral trapping was predicted to be important only at low water–rock ratios, accounting for a maximum of 2% of the added CO 2 at the lowest water–rock ratio investigated of 10:1, which corresponds to a small porosity increase of approximately 0.14% to 0.15%.
    Print ISSN: 1075-9565
    Electronic ISSN: 1526-0984
    Topics: Geography , Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 47
    Publication Date: 2017-11-16
    Description: This paper shows how nonuniform source–receiver spacing in a three-dimensional (3-D) land acquisition creates footprints that could easily be mistaken for geology. In a 3-D time-migrated seismic volume from the midcontinent United States, amplitude extraction along the top of the Mississippian limestone formation shows a sinkhole-like feature, which is justified from a depositional perspective. However, an inspection of the acquisition layout shows that the sinkhole is a replica of the fold distribution. In land surveys where source and receivers seldom have a regular distribution and for unconventional plays that are not developed through patterned drilling, a thorough review of processing and acquisition parameters is necessary before interpreting amplitude maps.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 48
    Publication Date: 2017-11-16
    Description: Fresh cores from tight-rock samples of subsurface hydrocarbon reservoirs retain mobile fluids. These fluids have complex chemical compositions and a large spectrum of molecules with different diameters and polarities. When investigated using high-resolution field-emission scanning electron microscopy (SEM), the imposed vacuum over hours of time causes pore fluids trapped in the rock sample to flow and interact with the mineral matrix. This paper reports the capillary fluid dynamics effect observed on freshly milled cross sections of tight chalk at high resolution. Multiphase fluid dynamic simulations confirm the aggregation of heavier fluid molecules on the geometrical irregularities of the pore space. As a consequence of this pitfall, the differentiation of solid organic matter versus variably viscous hydrocarbons from SEM data is subject to a fundamental revision.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 49
    Publication Date: 2017-01-16
    Description: The Lower Cretaceous stratigraphic section in the northern Gulf of Mexico (GOM) comprises several well-documented carbonate systems that have prominent shelf-margin buildups, including the Berriasian Knowles Limestone ramp and shelf system, Barremian Sligo Formation shelf system, Aptian Pearsall Formation ramp system, and shelf systems of the Albian Glen Rose, Edwards, and Stuart City Formations. Two lesser-known but large-scale Lower Cretaceous Valanginian carbonate shelf to shelf-margin systems are documented in this investigation using core, wireline-log, and regional two-dimensional seismic data. The platform-margin succession of the older Calvin section comprises a shelf-margin buildup (back reef, reef, and fore reef facies) that may be as thick as 2000 ft (610 m). The seaward margin of the shelf, as displayed by seismic data, suggests shelf-to-basin relief of as much as 1000 ft (305 m) and margin-to-lagoon relief of 200 to 500 ft (60 to 140 m) (relief estimates are not decompacted). Major reef-building organisms are Lithocodium , stromatoporoids, and corals. The Winn limestone is younger than the Calvin limestone, and at the shelf margin, it may have been 600 to 800 ft (180 to 245 m) thick. It is composed of organisms similar to those of the Calvin reef complex. Considering the vertical position of the Calvin platform, succeeding the major bypass of Calvin lowstand siliciclastic sands, the platform probably records a transgression, which is consistent with its highly aggradational depositional style. The Winn shelf margin was initiated landward of the Calvin shelf margin and did not prograde as far seaward as the Calvin shelf margin. The recognition of these two Lower Cretaceous carbonate systems is important because they further detail the stratigraphic history and architecture of this deeply buried, lowermost Lower Cretaceous section in the GOM. These formations are also potential deep-gas, tight-carbonate (low-porosity) plays.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 50
    Publication Date: 2017-09-19
    Description: Development of geothermal energy in sedimentary basins is an attractive option given the availability of data from the oil and gas industry. Previous geothermal studies in sedimentary basins have focused on temperatures and petrophysical properties. In this study, the focus is placed on historical reservoir performance. In the Western Canada Sedimentary Basin, estimated temperatures and measured fluid production and injection rates at existing wells are combined to provide a per-well estimate of thermal power production. Nearly 700 of these hypothetical geothermal wells would produce 1 MW of power, and a total of 6 GW could be produced if all wells were converted to geothermal wells. Many of these wells may not be suitable for immediate use because of temperature anomalies resulting from injection of cooler water into target strata. Further research is needed to characterize the magnitude and extent of these anomalies. Geothermal potential should also be considered in the development of oil and gas resources in sedimentary basins.
    Print ISSN: 1075-9565
    Electronic ISSN: 1526-0984
    Topics: Geography , Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 51
    Publication Date: 2017-09-19
    Description: The stress regime in the Illinois Basin was investigated to assess how the rock column might respond to the injection of fluids, including coproduced formation brines and supercritical CO 2 .This response is a concern because injection practices could increase pore fluid pressure and potentially induce seismicity. Data were collected to determine the magnitude and orientation of a three-component stress field: vertical stress ( S v ) and minimum ( S h ) and maximum ( S H ) horizontal stresses. The S v was evaluated with a six-layer lithostratigraphic column. A two-layer pressure–depth S v model was generated for the central part of the basin, and a single pressure gradient model was constructed for the surrounding region. In the central part of the basin, the S v gradient is 24.9 MPa/km (1.11 psi/ft) to a depth of 2134 m (7000 ft), followed by a gradient of 27.1 MPa/km (1.20 psi/ft) below 2134 m (7000 ft). For the area surrounding the deep basin, the S v gradient was 25.5 MPa/km (1.13 psi/ft). The S h was evaluated from multiple data sources, primarily hydraulic fracture records or extended leak-off tests. The S h gradient calculations ranged from 24.1 to 27.3 MPa/km (1.07 to 1.21 psi/ft). The S h values for the basal Paleozoic clastic units are lower than those for units in the overlying horizons. The S H was based on a critically stressed model yielding values between 40.0 and 82.6 MPa/km (1.77 to 3.65 psi/ft). Stress orientation data for the Illinois Basin were collected from multiple sources. The orientation of S H across the study area is relatively uniform in strike at approximately N60°E. Marked deviations in S H result from localized structural discontinuities.
    Print ISSN: 1075-9565
    Electronic ISSN: 1526-0984
    Topics: Geography , Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 52
    Publication Date: 2017-06-22
    Description: Surface and airborne gas monitoring programs are becoming an important part of environmental protection in areas favorable for subsurface storage of carbon dioxide. Understanding structural architecture and its effects on the flux of fluids, specifically CO 2 and CH 4 , in the shallow subsurface and atmosphere is helping with designing and implementing next-generation monitoring technologies, including unmanned aerial vehicles (UAVs). An important aspect of this research is using subsurface fracture data to inform the design of flight pathways for UAVs in the Farnsworth oil unit of the Anadarko Basin. The target zone for CO 2 storage and enhanced oil recovery in the Farnsworth oil unit is in the upper Morrow sandstone at subsurface depths greater than 2000 m (6562 ft). Field study reveals that sandstone and chert in the High Plains Aquifer contain numerous joints that provide crucial insight into aquifer architecture and subsurface flow pathways. Properties of more than 1700 joints were measured in the field and in high-resolution satellite images. Two distinctive joint systems interpreted as a conjugate pair were identified in the study area. Joint spacing follows a lognormal statistical scaling rule. These fractures appear to be the product of an east–northeast regional compressive stress and may have a significant effect on flow in the High Plains Aquifer system. Based on the results of this research, design of UAV flight paths should be oblique to fractures in a way that maximizes the likelihood of CO 2 and CH 4 flux of systematic joints and cross joints.
    Print ISSN: 1075-9565
    Electronic ISSN: 1526-0984
    Topics: Geography , Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 53
    Publication Date: 2017-07-18
    Description: The structural history of the Mississippi Canyon, Atwater Valley, western DeSoto, and western Lloyd Ridge protraction areas in the northeastern deep-water Gulf of Mexico is of a basin influenced by complex salt tectonics that controlled the formation of intraslope minibasins and sediment distribution. Large volumes of Middle Jurassic autochthonous salt (Louann Salt) were successively mobilized upward into younger sediments, forming three distinctive allochthonous salt layers: at the top Barremian, at the top Cretaceous, and within the Neogene interval. Four types of Neogene allochthonous salt systems are identified based on the geometry of the allochthonous salt bodies and associated faults, folds, and minibasins: (1) basement-controlled, (2) counterregional, (3) roho, and (4) fold-belt–related salt systems. The allochthonous salt systems are defined based on salt-body geometry, salt-stem geometry, associated fault network, and associated stratigraphic geometries. The distribution of the Neogene allochthonous salt systems is controlled by the original autochthonous salt thickness, the basement configuration, and the regional sediment-loading pattern. The basement-controlled Neogene salt systems are present in the eastern and northern part of the study area where little basinward gravitational gliding occurred. The counterregional and roho allochthonous salt systems are associated with the basinward evacuation of salt in response to extensive sediment loading. The fold-belt–related allochthonous salt systems are present in the southern part of the salt province where extensive shortening remobilized salt into and onto contractional structures. The detailed study of those Neogene allochthonous salt systems is used to build conceptual kinematic models for each style of salt system.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 54
    Publication Date: 2017-07-18
    Description: The structural framework and evolution from the Middle Jurassic to the present of the Mississippi Canyon, Atwater Valley, western DeSoto Canyon, and western Lloyd Ridge protraction areas consist of a complex history influenced by basement fabric, multiple stages of salt movement, and gravitational gliding. A detailed tectono-stratigraphic interpretation of the study area indicates that three main stages of salt movement controlled sediment dispersal patterns and the formation and evolution of intraslope minibasins. These three stages of salt movement occurred during the Cretaceous, the Paleogene, and the Neogene. Basement structures were the primary control on initial salt kinematics, affecting gravity-driven slope deformation and resulting in a wide variety of structural styles. Basement (acoustic basement) structures (horsts, grabens, and half grabens) formed prior to the deposition of the Middle Jurassic autochthonous Louann Salt. These features are interpreted to have controlled the original thickness of the autochthonous salt layer and subsequent salt-withdrawal patterns. Mesozoic structures, such as extensional-compressional gliding systems and expulsion rollovers, formed above the autochthonous salt. Three levels of allochthonous salt systems are identified: (1) approximate top Barremian, (2) top Cretaceous, and (3) intra-Neogene (between 10 and 4 Ma). Early emplacement of two allochthonous salt layers is present in the northeastern part of the study area, whereas the Neogene allochthonous salt system extends throughout the Mississippi Canyon, western DeSoto Canyon, and northern Atwater Valley protraction areas. Salt from the autochthonous and two deep allochthonous salt layers was expelled vertically and basinward during the Neogene, feeding the younger allochthonous salt systems. The autochthonous and deep allochthonous salt layers were detachments for many of the large Neogene extensional (growth faults and turtles) and contractional (anticlines and thrust faults) structures, whereas the Neogene allochthonous salt system accommodated suprasalt minibasins associated with counterregional and roho salt systems. These three allochthonous salt layers were successively loaded by gravity-flow sediments, resulting in deep (above autochthonous or deep allochthonous salt layers) and shallow (supra-Neogene allochthonous salt) minibasin formations and local development of extensive salt welds. Northwest–southeast-oriented strike-slip structures, active during the Neogene, are present in the salt province within the study area. They are related to basinwide heterogeneities in the salt distribution and are controlled by differential basinward movement of adjacent suprasalt minibasins.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 55
    Publication Date: 2017-06-16
    Description: The deep high-temperature, high-pressure Lower Cretaceous Bashijiqike sandstone (buried to depths as great as 6.5–7.1 km [21,325–23,293 ft]) is an important natural gas reservoir in Keshen gas field, Kuqa depression of the Tarim basin. Reservoir quality is a critical risk factor in the development of these ultradeep reservoirs. Integrated approaches incorporating routine core analyses and mineralogical, petrographic, and geochemical analyses have been used to investigate the diagenetic history of these rocks and their effect on reservoir quality with the aim to unravel the mechanisms for maintaining anomalously high porosities in sandstones that are buried to such a great depth. These sandstones are dominantly fine- to medium-grained, moderately to well-sorted lithic arkoses and feldspathic litharenite. Most primary pores have been lost by mechanical compaction or carbonate cementation, and the reduction of porosity by mechanical compaction was more significant than that by cementation. Dissolution of framework grains contributed to the enhancement of reservoir quality. Eogenetic diagenetic alterations mainly include mechanical compaction, precipitation of calcite cements, and grain-coating clays, and mesogenetic diagenesis is characterized by dissolution of framework grain by organic acids and subsequent precipitation of clay minerals and quartz. Infiltration of meteoric water related to teleodiagenesis would result in dissolution of the framework grains. The meteoric leaching events during teleodiagenesis are of great importance for the Bashijiqike sandstones. Grain-coating clay minerals (mixed-layer illite/smectite clays) help to preserve porosity at depth by retarding quartz cementation and pressure solution. The unique burial regime as early-stage shallow burial with late-stage rapid deep burial contributes to porosity preservation in eodiagenesis. Fluid overpressure caused by intense structural compression in the middle Himalayan movement retarded compaction and helped preserve porosity in the late rapid deep burial stage. Anomalously high porosities are mainly found in medium-grained, well-sorted sandstones with grain-coating clays but with low clay and carbonate cement content, of which the porosity is preserved primarily and enhanced secondarily. The lowest porosities are associated with sandstones that are tightly compacted or cemented with carbonates or rich in detrital matrix. Porosity–depth trends may vary significantly with lithofacies because of their differences in textural and compositional attributes. Five lithofacies are defined in terms of detrital composition and texture and type and degree of diagenesis. The reservoir quality prediction models of various litho-facies are constructed, and the results of this study provide insights into mechanisms for maintaining anomalously high porosity and permeability in high-temperature, high-pressure sandstone reservoirs and may help explain hydrocarbon distribution.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 56
    Publication Date: 2013-10-04
    Description: An interpretation of geologic structure at King Sound in the Canning Basin was completed using airborne gravity gradient, magnetic, and seismic data. During the Late Devonian and Mississippian periods, the elevated part of the basement in the north was rimmed by carbonate reefs and redeposited carbonate debris, whereas in the south, siliciclastic submarine fans and turbidites were deposited along the margin of the basement in a deep-marine environment. Three principal lithologic units were identified from the vertical gravity gradient ( G DD ) in the basin: (1) the Fairfield Group carbonates of high density are interpreted to be the source of prominent positive gravity anomalies; (2) forereef debris and carbonate clastics reworked from carbonates higher up the slope or from the carbonate platform are interpreted to be the source of medium-density responses; and (3) turbidites, debris flows, and associated clastic basinal sequences of low density are interpreted to be the source of prominent negative gravity anomalies. Depth slices of G DD indicate the channelized nature of turbidite flows. In the lower section of the basin, intrasedimentary intrusives were identified from magnetic, G DD , seismic, and well data. Depth to magnetic basement calculation indicates that the surface of the Archean to Paleoproterozoic basement ranges from 3200 to 130 m (10,499–427 ft) below sea level. The northwest- and northeast-oriented south-dipping faults cut the basement and propagate upward into the sediments. A three-dimensional geologic model constructed for King Sound satisfies all known geologic constraints and is consistent with the gravity, magnetic, seismic, and well data.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 57
    Publication Date: 2013-10-04
    Description: The process and mechanisms of secondary hydrocarbon migration in the Tazhong uplift, Tarim Basin, were investigated based on the analysis of the regional structure and by integrating geologic, hydrodynamic, and geochemical parameters. Parameters successfully analyzed included the fluid potential, fluid properties, production outputs, and diamantane index. The results indicated that hydrocarbons migrated into the Tazhong uplift from the northern part of the Manjiaer depression through a series of injection points (IPs) during four orogenies, that is, the early Caledonian (510 Ma), the late Caledonian (439 Ma), the late Hercynian–Indosinian (290 Ma), and the Yanshanian–Himalayan (208 Ma). A total of six IPs were identified at the intersections of the northeast-trending faults and the northwest-trending flower strike faults. The hydrocarbons migrated from the IPs into traps along regional trends from northwest to southeast and from northeast to southwest. The hydrocarbon migration process and patterns determined the distribution of hydrocarbon properties and production rates in the Tazhong uplift. With increasing distance from the IPs, daily hydrocarbon production decreases, and the hydrocarbons become progressively heavier and display lower gas:oil ratios.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 58
    Publication Date: 2013-10-04
    Description: The Molasse deposits of the Central Eastern Alps are partly incorporated into a fold and thrust belt that recently has come into exploration focus. The structural style and timing of deformation varies significantly alongstrike. Regional three-dimensional seismic and well data interpretation indicate three different structural segments from east to west: (1) The Sierning imbricates have a decollement close to the base of the Molasse sequence and consist of varying numbers of thrust sheets alongstrike. Early Miocene shortening of the Molasse is at least 6.2 km (3.9 mi). Overthrusting of the internal Penninic and Helvetic wedge since the Oligocene accommodated at least 25 km (15.5 mi) of additional shortening. (2) The Regau segment is dominated by one to two small thrust sheets above a shallow detachment. This segment is dominated by overthrusting of the Alpine wedge. (3) The Perwang imbricates consist of an Oligocene wedge with complex deformed thrust sheets above a detachment horizon in Upper Cretaceous marls. Minimum shortening in the imbricates is 18.5 km (11.5 mi) with overthrusting 33.3 km (20.7 mi). All shortening estimates have an uncertainty of approximately 20% to 35%. The laterally varying thrust-belt architecture results from predeformational conditions (e.g., sediment thickness, mechanical stratigraphy, and basement dip). In the Sierning imbricates, hydrocarbon trap definition and charge issues are exploration risks. In the Regau segment, exploration is focused on the subthrust play. The Perwang imbricates have hydrocarbon shows but no economic discoveries. Charge and seal issues are the main risks. The petroleum systems in the context of the structural evolution are not yet fully understood.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 59
    Publication Date: 2013-08-03
    Description: The Heidrun field, located on the Halten Terrace of the mid-Norwegian continental shelf, was one of the first giant oil fields found in the Norwegian Sea. Traditional reservoir intervals in the Heidrun field lie within the Jurassic synrift sequence. Most Norwegian continental shelf fields have been producing from these Jurassic reservoirs for the past 30 yr. Production has since declined in these mature fields, but recently, exploration for new reservoirs has resurged in this region. The Jurassic rifted fault blocks form a narrow continental shelf in Norway, thereby greatly reducing the areal extent for exploration and development within existing fields. As the rift axis is approached farther offshore, these Jurassic reservoirs become very deep, too risky to drill, and uneconomical. This risk has prompted exploration in more recent years of the shallower Cretaceous, postrift stratigraphic succession. Cretaceous turbidites have been found in the Norwegian and North Seas, and the discovery of the Agat field in the Norwegian North Sea confirms the existence of a working petroleum system capable of charging Cretaceous reservoirs. These Cretaceous reservoirs were deposited as slope- and basin-floor fans within a series of underfilled rifted deeps along the Norwegian continental shelf and are thought to be sourced from the localized erosion of Jurassic rifted highs. We use three-dimensional seismic and well data to document the geomorphology of a deep-water, Lower Cretaceous wedge (Cromer Knoll Group) within the hanging wall of a rift-related half graben formed on the Halten Terrace offshore mid-Norway. Seismic attribute extractions taken within this Lower Cretaceous wedge reveal the presence of several lobate to elongated bodies that seem to cascade over fault-bounded terraces associated with rifted structures. These high-amplitude, elongated bodies are interpreted as deep-water sedimentary conduits that are time equivalent to the Cretaceous basin-floor fans in more distal parts of the basin to the west. These half-graben fills have the potential to contain high-quality Cretaceous sandstones that might represent a potential new reservoir interval within the Heidrun field.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 60
    Publication Date: 2013-08-03
    Description: The fact that velocity models based on seismic reflection surveys commonly do not consider the near-surface geology necessitates filling the gap between the top of a velocity model and the surface of the Earth. In this study, we present a new workflow to build a shallow geologic model based exclusively on borehole data and corroborated by laboratory measurements. The study area is in Chémery (France), located at the southwestern border of the Paris Basin, where a large amount of borehole data is publicly available. The workflow starts with identifying lithologic interfaces in the boreholes and interpolating them between the boreholes. The three-dimensional (3-D) geometry of the lithologies then allows interpretation of the position, orientation, and offset of fault planes. Given the importance of the fault interpretation in the modeling process, a combination of different approaches is used to obtain the most reasonable structural framework. After creating a 3-D grid, the resulting 3-D structural model is populated with upscaled velocity logs from the boreholes, yielding the final near-surface P-wave velocity model. To better constrain the velocity model, we conducted laboratory measurements of P- and S-wave velocities in dry and water-saturated conditions on all lithologies in the model. The laboratory data were used to populate the 3-D near-surface model with V P / V S ratio values. The presented workflow accounts for one-dimensional borehole data and is much more iterative and time-consuming than workflows based on two-dimensional seismic sections. Nevertheless, the workflow results in a robust 3-D near-surface model allowing for structural interpretations and revealing the 3-D seismic velocity field.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 61
    Publication Date: 2013-09-14
    Description: Quartz is the principal framework mineral in clastic sediment reservoirs. In a frontier basin with sparse wells, the source of quartz in sandstones may be a predictor of the availability of medium- to coarse-grained quartz sand from plutonic sources, likely to provide good reservoirs. The Scotian Basin, offshore eastern Canada, was used to test this hypothesis because of its well-understood provenance history and geographic variability in known medium- to coarse-grained reservoir sandstones. The sources of detrital quartz in fine-grained sandstones were determined using hot-cathode cathodoluminescence (CL), supplemented by other petrographic techniques. The CL color shift for different quartz types was calibrated against the CL properties of representative source rocks in the hinterland, because generalizations in the literature do not precisely match our basin-specific observations. Grain size of sandstone exerts a strong control over quartz type, with plutonic-hypabyssal quartz and high-grade metamorphic quartz more abundant in coarse-grained sandstones and low-grade metamorphic quartz more abundant in fine-grained sandstones. Nevertheless, the analysis of fine-grained sandstones shows that plutonic-hypabyssal quartz is more abundant in fine-grained sandstones of the Sable subbasin than in those of the Abenaki subbasin. The abundance of plutonic-hypabyssal quartz correlates with the abundance of medium- to coarse-grained sandstone reservoirs in the Sable subbasin. This study suggests that, in frontier basins, the abundance of plutonic-hypabyssal quartz in fine-grained sandstones can be used as an indicator of available medium- to coarse-grained sandstone reservoir.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 62
    facet.materialart.
    Unknown
    American Association of Petroleum Geologists (AAPG)
    Publication Date: 2013-09-14
    Description: In western Greece, the Ionian and pre-Apulian zones represent, respectively, the basin and the transitional zone (slope) to the Apulian platform. The Apulian platform constitutes the weakly deformed foreland of the external Hellenides. The pre-Apulian zone appears in the Ionian Islands and the eastern Ionian Sea, whereas the Apulian platform is exclusively found in the Ionian Sea. The Ionian zone consists of Triassic evaporites, Jurassic–upper Eocene (mostly pelagic carbonates, minor cherts, and shales), overlain by the Oligocene flysch. Organic-rich source rocks occur within Triassic evaporites and Jurassic–Cretaceous pelagic argillaceous-siliceous rocks. The pre-Apulian zone consists of Triassic to Miocene deposits, mainly mixed neritic-pelagic carbonates. Hydrocarbon source rocks include pelagic and hemipelagic deposits rich in marine organic material, although terrigenous organic matter is also found in siliciclastic layers. Apulian platform source rocks are mainly the organic-rich shales within the Triassic Burano evaporites. Western Greece contains major petroleum systems, which extend into the Ionian Sea. Ionian, pre-Apulian, and Apulian petroleum systems contribute to the probable hydrocarbon accumulations within the big offshore (Ionian Sea) anticlines. Western Greece contains important oil and gas shale reservoirs with a potential of unconventional exploration. Promising areas for hydrocarbons need systematic and detailed three-dimensional seismic data. Exploration for conventional petroleum reservoirs, through the interpretation of seismic profiles and the abundant surface geologic data, will provide the subsurface geometric characteristics of the unconventional reservoirs. Their exploitation should follow that of conventional hydrocarbons to benefit from the anticipated technological advances, eliminating environmental repercussions.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 63
    Publication Date: 2013-09-14
    Description: This work discusses concepts related to the occurrence of salt along weakness planes, such as faults and fractures, which resemble igneous intrusions and may result in peculiar seismic features. We suggest that mechanisms for the formation of these structures basically involve the creation of extensional faults (commonly associated with crestal collapse grabens), which are rotated and migrated to structural flanks by domation, creating interesting seismic features here referred to as halokinetic rotating faults. At the time of their formation, some of these faults may be incipiently intruded by salt as a way of relieving sporadic intense internal overpressure episodes in the salt body, by regional compression, and/or by buoyancy effects compensating the density difference between salt and surrounding sediments. The relatively low overburden pressure at the crest of the diapir and the original high dip angles of these fault planes favor salt intrusions near the diapir apex. The process may occur in several cycles along the salt dome evolution, creating several generations of salt apophyses positioned in the diapir apex and flanks, resulting in different dips and areas of extension. These intrusions sometimes resemble the branches of Christmas tree structures, which are commonly formed by extrusive mechanisms. Although well and seismic data point to the occurrence of salt along fault planes, we recognize that salt is not a low-viscosity fluid, and the mechanisms to allow its penetration along fault planes remain unknown. Some of the possible mechanisms, which are commonly associated with a later phase of regional compression, are discussed in this work. The implications for petroleum exploration may have been overlooked in the recent exploration campaigns in the deep-water regions of the Brazilian margin. Halokinetic rotating faults, when partially filled with salt, are sometimes responsible for common pitfalls observed in seismic and well data interpretation. When fault planes present subhorizontal dips and high reflectivity, caused by the presence of salt, they have been mistakenly interpreted as flatspots, a well-known seismic hydrocarbon indicator. When drilled and proved to correspond to thin evaporite intervals in well data, these salt apophyses have also been misinterpreted as younger localized evaporitic events overlying the main salt body.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 64
    Publication Date: 2013-09-20
    Description: The Cretaceous rocks of Florida have been recognized as potentially suitable reservoirs for geologic carbon dioxide (CO 2 ) sequestration. Specifically, the upper member of the Upper Cretaceous Lawson Formation, together with the lower part of the Paleocene Cedar Keys Formation, is presented here as a potential composite CO 2 storage reservoir that is mainly composed of porous dolostone sealed by thick anhydrites of the overlying middle Cedar Keys Formation. Many of the porous intervals within the Cedar Keys-Lawson storage reservoir display lateral continuity and have an average porosity range of 20%–30%. The estimated CO 2 storage capacity for the reservoir is approximately 97 billion t of CO 2 , which means the Lawson and Cedar Keys Formations composite reservoir could potentially support CO 2 sequestration for hundreds of large-scale power plants in the southeastern United States for their entire 40-yr lifespan. Because most of the previous research on the Lawson Formation is concentrated in north-central and northeastern Florida and southern Georgia, this study further characterizes the formation and its CO 2 sequestration potential in south-central and southern Florida.
    Print ISSN: 1075-9565
    Electronic ISSN: 1526-0984
    Topics: Geography , Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 65
    Publication Date: 2013-10-04
    Description: The evolution of porosity in shales with increasing maturity was examined in a suite of five New Albany Shale samples spanning a maturity range from immature (vitrinite reflectance, R o 0.35%) to postmature (R o 1.41%). Devonian to lower Mississippian New Albany Shale samples from the Illinois Basin used in this study contain marine type II kerogen having total organic carbon contents from 1.2 to 13.0 wt. %. Organic petrology, CO 2 and N 2 low-pressure adsorption, and mercury intrusion capillary pressure techniques were used to quantify pore volumes, pore sizes, and pore-size distributions. Increasing maturity of the New Albany Shale is paralleled by many changes in the characteristics of porosity. The total porosity of 9.1 vol. % in immature New Albany Shale decreases to 1.5 vol. % in the late mature sample, whereas total pore volumes decrease from 0.0365 to 0.0059 cm 3 /g in the same sequence. Reversing the trend at even higher maturity, the postmature New Albany Shale exhibits higher porosity and larger total pore volumes compared to the late mature sample. With increasing maturity, changes in total porosity and total pore volumes are accompanied by changes in pore-size distributions and relative proportions of micropores, mesopores, and macropores. Porosity-related variances are directly related to differences in the amount and character of the organic matter and mineralogical composition, but maturity exerts the dominant control upon these characteristics. We conclude that organic matter transformation due to hydrocarbon generation and migration is a pivotal cause of the observed porosity differences.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 66
    facet.materialart.
    Unknown
    American Association of Petroleum Geologists (AAPG)
    Publication Date: 2013-10-04
    Description: We present a new hypothesis for the Jurassic plate-tectonic evolution of the Gulf of Mexico basin and discuss how this evolution influenced Jurassic salt tectonics. Four interpretations, some based on new data, constrain the hypothesis. First, the limit of normal oceanic crust coincides with a landward-dipping basement ramp near the seaward end of the salt basin, which has been mapped on seismic data. Second, the deep salt in the deep-water Gulf of Mexico can be separated into provinces on the basis of position with respect to this ramp. Third, paleodepths in the postsalt sequence indicate that salt filled the Gulf of Mexico salt basin to near sea level. Fourth, seismic data show that postsalt sediments in the central Louann and the Yucatan salt basins exhibit large magnitudes of Late Jurassic salt-detached extension not balanced by equivalent salt-detached shortening. In our hypothesis, Callovian salt was deposited in preexisting crustal depressions on hyperextended continental and transitional crust. After salt deposition ended, rifting continued for another 7 to 12 m.y. before sea-floor spreading began. During this phase of postsalt crustal stretching, the salt and its overburden were extended by 100 to 250 km (62–155 mi), depending on location. Sea-floor spreading divided the northern Gulf of Mexico into two segments, separated by the northwest-trending Brazos transform. The eastern segment opened from east to west, leaving the Walker Ridge salient in the center of the basin as the final area to break apart. In some areas, salt flowed seaward onto new oceanic crust, first concordantly over the basement as a parautochthonous province, then climbing up over stratigraphically younger strata as an allochthonous province.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 67
    Publication Date: 2013-08-03
    Description: Using diverse geologic and geophysical data from recent exploration and development, and experimental results of analysis of gas content, gas capacity, and gas composition, this article discusses how geologic, structural, and hydrological factors determine the heterogeneous distribution of gas in the Weibei coalbed methane (CBM) field. The coal rank of the Pennsylvanian no. 5 coal seam is mainly low-volatile bituminous and semianthracite. The total gas content is 2.69 to 16.15 m 3 /t (95.00–570.33 scf/t), and gas saturation is 26.0% to 93.2%. Burial coalification followed by tectonically driven hydrothermal activity controls not only thermal maturity, but also the quality and quantity of thermogenic gas generated from the coal. Gas composition indicates that the CBM is dry and of dominantly thermogenic origin. The thermogenic gases have been altered by fractionation that may be related to subsurface water movement in the southern part of the study area. Three gas accumulation models are identified: (1) gas diffusion and long-distance migration of thermogenic gases to no-flow boundaries for sorption and minor conventional trapping, (2) hydrodynamic trapping of gas in structural lows, and (3) gas loss by hydrodynamic flushing. The first two models are applicable for the formation of two CBM enrichment areas in blocks B3 and B4, whereas the last model explains extremely low gas content and gas saturation in block B5. The variable gas content, saturation, and accumulation characteristics are mainly controlled by these gas accumulation models.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 68
    Publication Date: 2013-08-03
    Description: Prolific hydrocarbon discoveries in the subsalt, commonly known as the "presalt," section of Brazil and the conjugate African margin have created a business imperative to predict reservoir quality in lacustrine carbonates. Geothermal convection is a style of groundwater flow known to occur in rift settings, which is capable of diagenetic modification of reservoir quality. We simulated variable density groundwater flow coupled with chemical reactions to evaluate the potential for diagenesis driven by convection in subsalt carbonates. Rates of calcite diagenesis are critically controlled by temperature gradient and fluid flux following the principles of retrograde solubility. Simulations predict that convection could operate in rift carbonates prior to salt deposition, but with rates of dissolution in the reservoir interval only on the order of 0.01 vol. %/m.y., which is too low to significantly modify reservoir quality. The exception is around permeable fault zones and/or unconformities where flow is focused and dissolution rates are amplified to 1 to 10 vol. %/m.y. and could locally modify reservoir quality. After salt deposition, simulations also predict convection with a critical function for salt rugosity. The greatest potential for dissolution at rates of 0.1 to 1 vol. %/m.y. occurs where salt welds, overlying permeable carbonates thin to 500 m (1640 ft) or less. With tens of million years residence times feasible, convection under these conditions could locally result in reservoir sweet spots with porosity modification of 1% to 10% and potentially an order of magnitude or more in reservoir permeability. Integrating quantitative model-derived predictive diagenetic concepts with traditional subsurface data sets refines exploration to production scale risking of carbonate reservoir presence and quality.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 69
    Publication Date: 2013-08-03
    Description: Anomalously high porosities and permeabilities are commonly found in the fluvial channel sandstone facies of the Triassic Skagerrak Formation in the central North Sea at burial depths greater than 3200 m (10,499 ft), from which hydrocarbons are currently being produced. The aim of our study was to improve understanding of sandstone diagenesis in the Skagerrak Formation to help predict whether the facies with high porosity may be found at even greater depths. The Skagerrak sandstones comprise fine to medium-grained arkosic to lithic-arkosic arenites. We have used scanning electron microscopy, petrographic analysis, pressure history modeling, and core analysis to assess the timing of growth and origin of mineral cements, with generation, and the impact of high fluid pressure on reservoir quality. Our interpretation is that the anomalously high porosities in the Skagerrak sandstones were maintained by a history of overpressure generation and maintenance from the Late Triassic onward, in combination with early microquartz cementation and subsequent precipitation of robust chlorite grain coats. Increasing salinity of pore fluids during burial diagenesis led to pore-filling halite cements in sustained phreatic conditions. The halite pore-filling cements removed most of the remaining porosity and limited the precipitation of other diagenetic phases. Fluid flow associated with the migration of hydrocarbons during the Neogene is inferred to have dissolved the halite locally. Dissolution of halite cements in the channel sands has given rise to megapores and porosities of as much as 35% at current production depths.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 70
    Publication Date: 2013-09-14
    Description: Cenozoic rifted lacustrine basins in east China display three main basin types: (1) basins with steeply dipping boundary fault, whose hanging walls tilt along pivot points; (2) basins with listric boundary faults, whose hanging walls bend along flexural bending points; and (3) basins formed by earlier extensional rifting with later strike-slip movement superimposed. The sequence development is intimately linked to the tectonic movements in the area, where second-order sequences are regionally correlatable from basin to basin and relate to the large-scale tectonic movements in the region. Third-order sequences are related to local tectonic activity and are correlatable within basins, between subbasins, and sometimes, between neighboring basins. Detailed sequence-stratigraphic analysis and mapping of depositional systems demonstrate that sand-body distribution patterns are related to sequence-stratigraphic frameworks. For the three kinds of basins, the positions of pivot point zones, flexural bend zones, and strike-slip faults plus the syndepositional faults all control the distribution of depositional systems, systems tract, and sand bodies. These controlling factors can be attributed to different structural and stratigraphic features that change the accommodation. Structural elements include boundary faults, syndepositional faults, and abrupt changes in dip. Stratigraphic controls include preexisting surfaces with local channelization, paleobathymetric lows, and onlap onto clinoform slopes. The lowstand sand bodies deposited at the downdip end of these controlling factors constitute the current and future exploration targets for conventional reservoirs.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 71
    Publication Date: 2013-09-14
    Description: The three-dimensional (3-D) geometry of fractures and fault-related dolomite is difficult to access with classical subsurface prospection tools. Therefore, we have investigated an outcrop to improve the subsurface prediction for complex dolomite bodies. This outcrop is located in the Etoile massif (southeastern France) within a fault-bend anticline. The sedimentary units are of Upper Triassic to lower Barremian age. The fold results from the Pyreneo-Provençal shortening during the Late Cretaceous to the Eocene. The anticline hosts three types of dolomite bodies: (1a) massive dolomite of middle to late Oxfordian age, (1b) syndepositional stratabound dolomite of Tithonian age, and (2) isolated dolomite bodies associated with fractures and faults. Large-scale geometries of fault-related dolomite bodies have been modeled in 3-D. The 3-D geometries of these bodies show diapir-, finger- and wall-like structures. These bodies are located close to the main thrusts, in strata of middle Oxfordian to early Barremian age and are linked to the compressive fold-bending phase during the Late Cretaceous. Fault-related dolomitization occurred because of magnesium removal from the hydraulic brecciation and the pressure solution of type 1 dolomite with overpressured fluids. These fluids flushed upward along the main thrust and laterally by following the reservoir property contrasts in the host rocks. Fault-related dolomite bodies are either spread far apart from faults in grainy limestones with good initial reservoir properties or are restricted to fault vicinity in muddy limestones with poor initial reservoir properties. The study of the structural and stratigraphic framework was essential in the understanding of the dolomitization process.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 72
    Publication Date: 2013-09-14
    Description: Innovative seismic forward modeling is used to illustrate the sensitivity within seismic data, and its application in the interpretation of onlap and pinch-out of terminating deep-water sandstones, two critical components in deep-water exploration and production. Sandstone quality, net-to-gross estimates, volume calculations, vertical connectivity, and stratigraphic trapping are all dependent on the sandstone extent and their seismic characteristics in these settings. However, seismic resolution is commonly insufficient to resolve the critical reservoir parameters. Seismic modeling of termination styles based on integrated outcrop and subsurface properties allows for depth- and resolution-focused predictive models to be built for improved subsurface analysis. This technique is currently underused as a method to better understand the sensitivity of seismic data to the target lithologies and their geometries. The Grès d'Annot Formation is a well-studied sand-prone deep-water system of Paleogene age, deposited in a bathymetrically complex setting. Six end-member termination styles are discussed, including three sand-prone styles—simple onlap (O s ), draping onlap (O d ), and bed thickening (O t )—and three heterolithic styles—advancing pinch-out (P a ), convergent pinch-out (P c ), and convergent thickening and pinch-out (P ct ). Local thickening close to the system margins is common in both sand-prone and heterolithic terminating strata and plays an important function in the appropriate distribution of sandstone. The outcrops are interpreted as potential (process) analogs for the complex sandstone distribution and termination patterns observed in plays like the Paleogene of the Gulf of Mexico and the Jurassic of the northern North Sea.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 73
    Publication Date: 2013-09-14
    Description: We describe the structure, microstructure, and petrophysical properties of fault rocks from two normal fault zones formed in low-porosity turbiditic arkosic sandstones, in deep diagenesis conditions similar to those of deeply buried reservoirs. These fault rocks are characterized by a foliated fabric and quartz-calcite sealed veins, which formation resulted from the combination of the (1) pressure solution of quartz, (2) intense fracturing sealed by quartz and calcite cements, and (3) neoformation of synkinematic white micas derived from the alteration of feldspars and chlorite. Fluid inclusion microthermometry in quartz and calcite cements demonstrates fault activity at temperatures of 195°C to 268°C. Permeability measurements on plugs oriented parallel with the principal axes of the finite strain ellipsoid show that the Y axis (parallel with the foliation and veins) is the direction of highest permeability in the foliated sandstone (10 •2 md for Y against 10 •3 md for X, Z, and the protolith, measured at a confining pressure of 20 bars). Microstructural observations document the localization of the preferential fluid path between the phyllosilicate particles forming the foliation. Hence, the direction of highest permeability in these fault rocks would be parallel with the fault and subhorizontal, that is, perpendicular to the slickenlines representing the local slip direction on the fault surface. We suggest that a similar relationship between kinematic markers and fault rock permeability anisotropy may be found in other fault zone types (reverse or strike-slip) affecting feldspar-rich lithologies in deep diagenesis conditions.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 74
    Publication Date: 2013-07-03
    Description: Jurassic deposition in the Maghrebian tethys was governed by eustasy and rifting. Two periods were delineated: (1) a carbonate shelf (Rhaetian–early Pliensbachian) and (2) a platform-basin complex (early Pliensbachian–Callovian). The carbonate shelf evolved in four stages, generating three sedimentary sequences, J1 to J3, separated by boundary sea level falls, drawdown, exposure, and local erosion. Sediment facies bear evidence of sea level rises and falls. Lateral changes in lithofacies indicate shoaling and deepening upward during the Sinemurian. A major pulse of rifting with an abrupt transition from carbonate shelf to pelagic basin environments of deposition marks the upper boundary of the lower Pliensbachian carbonate shelf deposits. This rifting episode with brittle fractures broke up the Rhaetian–early Pliensbachian carbonate shelf and has created a network of grabens, half grabens, horsts, and stacked ramps. Following this episode, a relative sea level rise led to pelagic sedimentation in the rift basins with local anoxic environments that also received debris shed from uplifted ramp crests. Another major episode spanning the whole early Pliensbachian–Bajocian is suggested by early brecciation, mass flows, slumps, olistolites, erosion, pinch-outs, and sedimentary prisms. A later increase in the rates of drifting marked a progress toward rift cessation during the Late Jurassic. These Jurassic carbonates with detrital deposits and black shales as the source rocks in northeastern Tunisia may define interesting petroleum plays (pinch-out flanking ramps, onlaps, and structurally upraised blocks sealed inside grabens). Source rock maturation and hydrocarbon migration began early in the Cretaceous and reached a maximum during the late Tortonian–Pliocene Atlassic orogeny.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 75
    Publication Date: 2013-07-03
    Description: Isolated carbonate buildups (ICBs) are commonly attractive exploration targets. However, identifying ICBs based only on seismic data can be difficult for a variety of reasons. These include poor-quality two-dimensional data and a basic similarity between ICBs and other features such as volcanoes, erosional remnants, and tilted fault blocks. To address these difficulties and develop reliable methods to identify ICBs, 234 seismic images were analyzed. The images included proven ICBs and other features, such as folds, volcanoes, and basement highs, which may appear similar to ICBs when imaged in seismic data. From this analysis, 18 identification criteria were derived to distinguish ICBs from non-ICB features. These criteria can be grouped into four categories: regional constraints, analysis of basic seismic geometries, analysis of geophysical details, and finer-scale seismic geometries. Systematically assessing the criteria is useful because it requires critical evaluation of the evidence present in the available data, working from the large-scale regional geology to the fine details of seismic response. It is also useful to summarize the criteria as a numerical score to facilitate comparison between different examples and different classes of ICBs and non-ICBs. Our analysis of scores of different classes of features suggests that the criteria do have some discriminatory power, but significant challenges remain.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 76
    facet.materialart.
    Unknown
    American Association of Petroleum Geologists (AAPG)
    Publication Date: 2013-07-03
    Description: West Edmond field, located in central Oklahoma, is one of the largest oil accumulations in the Silurian–Devonian Hunton Group in this part of the Anadarko Basin. Production from all stratigraphic units in the field exceeds 170 million barrels of oil (MMBO) and 400 billion cubic feet of gas (BCFG), of which approximately 60 MMBO and 100 BCFG have been produced from the Hunton Group. Oil and gas are stratigraphically trapped to the east against the Nemaha uplift, to the north by a regional wedge-out of Hunton strata, and by intraformational diagenetic traps. Hunton Group reservoirs are the Bois d'Arc and Frisco Limestones, with lesser production from the Chimneyhill subgroup, Haragan Shale, and Henryhouse Formation. Hunton Group cores from three wells that were examined petrographically indicate that complex diagenetic relations influence permeability and reservoir quality. Greatest porosity and permeability are associated with secondary dissolution in packstones and grainstones, forming hydrocarbon reservoirs. The overlying Devonian–Mississippian Woodford Shale is the major petroleum source rock for the Hunton Group in the field, based on one-dimensional and four-dimensional petroleum system models that were calibrated to well temperature and Woodford Shale vitrinite reflectance data. The source rock is marginally mature to mature for oil generation in the area of the West Edmond field, and migration of Woodford oil and gas from deeper parts of the basin also contributed to hydrocarbon accumulation.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...