ALBERT

Description: We evaluated the geochemical transformations that would likely occur after injecting CO2 into a sandstone formation using The Geochemist's Workbench(R), with the intent of simulating CO2 solution and mineral storage mechanisms. We used a hypothetical reservoir intended to closely resemble the Lamotte Sandstone in southwest Missouri, a reservoir rock found at about 600-m (1970-ft) depth, well above the recommended depth for CO2 sequestration of 800 m (2625 ft). In the absence of specific water chemistry and lithology data for this formation at the proposed injection site, the model considered two best estimates of each input parameter. Carbon dioxide (CO2) sequestered in the dissolved phase was found to range between 76.74 and 76.80 g/kg free water, and the pH dropped from 7.7 to 4.8 after a 10-yr injection period. During a 50-yr postinjection interval with no additional CO2(g) added, the model predicted the pH to rise from 4.8 to 5.3 and various minerals to precipitate, among them magnesite, nontronite-Mg, and gibbsite, as well as smaller amounts of siderite and dolomite. Magnesite, siderite, and dolomite contribute to removal of carbon. In general, the model is very flexible, allowing the user to incorporate variations in temperature, pressure, water chemistry, solid-phase mineralogy, and kinetics. Modeling steps are described here as well as the results, which are all based in 1 kg of free water. To determine the total sequestration potential, transport modeling is needed, in addition to the geochemical modeling presented here.

Description: Engineered landfill liner systems are expensive to install and represent a challenge to several developing countries. Alternatively, native soils, preferentially clays, can be used as cost-effective bottom liners. The purpose of this work is to justify the reliance on the ability of the clays at the Kharga-Dakhla land stretch, Western Desert, Egypt, to act as a containment and barrier for pollutants that might be generated in a landfill leachate. This is particularly valid in hyperarid regions where many environmental requirements for landfill liner design are relaxed, as precipitation is rare and percolation to buried wastes is practically absent. The availability of native clays and clay-bearing sediments in the study area, both on surface and subsurface, makes it a potential landfill site. Collaborating techniques have been used to determine the mineralogical, geochemical, and geotechnical characteristics of the sediments constituting the Quseir Formation (Upper Cretaceous). These techniques include x-ray diffraction analysis, differential thermal analysis, cation exchange capacity (CEC), swelling properties, Atterberg limits, porosity, and hydraulic conductivity. The obtained results indicate that the investigated clayey sediments are dense and compact. They have low hydraulic conductivity that ranges from 1 x 10 -10 to 4.96 x 10 -11 cm/s, with moisture content that does not exceed 7%. The swelling values of samples containing smectite range between 250 and 500%. The plasticity limit of the red clay (floor of the Dakhla Oasis) ranges between 11 and 18%, which indicates its suitability as a landfill lining material. Values for CEC are generally high and increase with increasing smectite content. It reaches as much as 69 meq/100-g sample, indicating enhanced ability for natural attenuation and can act within the containment system for metal pollutants. The obtained mineralogical, geochemical, and geotechnical data suggest that the studied clays can be used, effectively, as a viable alternative liner system for solid waste and/or secured landfills, replacing the costly state of the art liner systems. Satisfying siting criteria, the availability of the clays, and the easy way and their low cost of extraction provide a cost-effective solution to the problem of landfill lining in developing countries.

Description: The Cambrian Mount Simon Sandstone is the major target reservoir for ongoing geologic carbon dioxide (CO 2) sequestration demonstrations throughout the midwest United States. The potential CO 2 reservoir capacity, reactivity, and ultimate fate of injected CO 2 depend on textural and compositional properties determined by depositional and diagenetic histories that vary vertically and laterally across the formation. Effective and efficient prediction and use of the available pore space requires detailed knowledge of the depositional and diagenetic textures and mineralogy, how these variables control the petrophysical character of the reservoir, and how they vary spatially. Here, we summarize the reservoir characteristics of the Mount Simon Sandstone based on examination of geophysical logs, cores, cuttings, and analysis of more than 150 thin sections. These samples represent different parts of the formation and depth ranges of more than 9000 ft (〉2743 m) across the Illinois Basin and surrounding areas. This work demonstrates that overall reservoir quality and, specifically, porosity do not exhibit a simple relationship with depth, but vary both laterally and with depth because of changes in the primary depositional facies, framework composition (i.e., feldspar concentration), and diverse diagenetic modifications. Diagenetic processes that have been significant in modifying the reservoir include formation of iron oxide grain coatings, chemical compaction, feldspar precipitation and dissolution, multiple generations of quartz overgrowth cementation, clay mineral precipitation, and iron oxide cementation. These variables provide important inputs for calculating CO 2 capacity potential, modeling reactivity, and are also an important baseline for comparisons after CO 2 injection.

Description: Subsurface geologic storage of carbon dioxide calls for sophisticated monitoring tools with respect to long-term safety and environmental impact issues. Despite extensive research, many factors governing the fate of injected carbon dioxide (CO2) remain unclear. To identify possible risks through leakage of the CO2 storage reservoir, a program for monitoring of the CO2 flux at the surface was started at the Ketzin test site, which allows to distinguish between natural temporal and spatial flux variations and a potential leakage. To gain adequate long-term baseline data on the local background CO2 flux variations, CO2 soil gas flux, soil moisture, and temperature measurements were conducted once a month during a 6-yr period. Furthermore, soil samples were analyzed for their organic carbon and total nitrogen contents. The mean flux of all sampling sites before the CO2 injection (2005-2007) was 2.8 {micro}mol m-2 s-1 (ranging from 2.4 to 3.5), with a Q10 factor of 2.4, and in the years after commencing injection (2009-2010), 2.4 {micro}mol m-2 s-1 (ranging from 2.2 to 2.5), with the same Q10 factor. The CO2 flux rate is mainly controlled by the soil temperature. A significant influence of diurnal temperature variation and soil moisture was not detected. The spatial variability of the CO2 flux among the 20 sampling locations ranges from 1.0 to 4.5 {micro}mol m-2 s-1, depending on the organic carbon and total nitrogen content of the soil. Through comparison with the long-term measurements, unusual high CO2 fluxes can theoretically be distinguished from natural variations.

Description: The Livingstone Range anticlinorium marks a hanging-wall ramp across which the Livingstone thrust cuts up eastward approximately 1000 m ([~]3280 ft) between regional decollements in the Devonian and the Jurassic strata. It is well exposed and provides actualistic models for exploration of analogous subsurface structures. More than 30 km (

Description: The velocity of elastic waves is the primary datum available for acquiring information about subsurface characteristics such as lithology and porosity. Cheap and quick (spatial coverage, ease of measurement) information of permeability can be achieved, if sonic velocity is used for permeability prediction, so we have investigated the use of velocity data to predict permeability. The compressional velocity from wireline logs and core plugs of the chalk reservoir in the South Arne field, North Sea, has been used for this study. We compared various methods of permeability prediction from velocities. The relationships between permeability and porosity from core data were first examined using Kozeny's equation. The data were analyzed for any correlations to the specific surface of the grain, Sg, and to the hydraulic property defined as the flow zone indicator (FZI). These two methods use two different approaches to enhance permeability prediction from Kozeny's equation. The FZI is based on a concept of a tortuous flow path in a granular bed. The Sg concept considers the pore space that is exposed to fluid flow and models permeability resulting from effective flow parallel to pressure drop. The porosity-permeability relationships were replaced by relationships between velocity of elastic waves and permeability using laboratory data, and the relationships were then applied to well-log data. We found that the permeability prediction in chalk and possibly other sediments with large surface areas could be improved significantly using the effective specific surface as the fluid-flow concept. The FZI unit is appropriate for highly permeable sedimentary rocks such as sandstones and limestones that have small surface areas.

Description: Multiple methods are currently used to collect, prepare, extract, and analyze near-surface migrated hydrocarbons from marine sediments to evaluate subsurface petroleum generation and entrapment. Few have been rigorously tested to evaluate their effectiveness. A Gulf of Mexico field calibration survey over the Marco Polo field was undertaken as part of an industry-funded research project to better understand previously published and unpublished seabed geochemical results and determine which gas and liquid hydrocarbon extraction methods best characterize migrated hydrocarbons in near-surface sediments. The Marco Polo calibration data set demonstrates the importance of targeted coring and sampling depth. To improve the detection of seabed migrated thermogenic hydrocarbons, core samples should be collected along major migration pathways (cross-stratal leakage features) identified by conventional deep seismic and high-resolution sea floor imaging. Not all targeted cores hit the designated feature, and thus, collecting replicates along key migration features is critical. Collecting sediment samples below the near-surface transition zone known as the "zone of maximum disturbance" is also important to avoid possible alteration effects and interference by recent organic matter. Geochemical analysis should include a full range of hydrocarbon types: light hydrocarbon gases (C1-C5), gasoline range (C5-C10+), and high-molecular-weight (HMW) hydrocarbons (C15+). The interstitial sediment gas data should be plotted on a total hydrocarbon gas ({Sigma} C1-C5) versus wet gas fraction ({Sigma} C2-C5/{Sigma} C1-C5) chart to identify background, fractionated, and anomalous populations. Compound-specific isotopic analysis on selected anomalous samples is critical to correctly identify migrated subsurface gases from near-surface generated microbial gases. Microdesorption bound gases did not provide gas compositions or compound-specific isotope ratios similar to the Marco Polo reservoir gases, and thus, the bound gas extraction is not recommended. A gasoline range analysis provides a new range of hydrocarbons rarely examined in surface geochemical studies that assist in identifying thermogenic hydrocarbons. Extraction gas chromatography and total scanning fluorescence (TSF) maximum fluorescence intensity provided information on the presence of thermogenic HMW hydrocarbons but did not work as well with the low-level microseepage samples. The TSF fluorogram signature was similar for both seep and regional reference (background) samples and did not help to identify migrated thermogenic hydrocarbons. The Marco Polo calibration study provides a framework to better understand how best to collect (targeted deep cores) and extract migrated hydrocarbons from near-surface marine sediments and to evaluate the results.

Description: The deeply buried synrift play of the South Viking Graben is characterized by highly variable reservoir quality. An integrated approach incorporating petrophysics, petrography, and one-dimensional basin modeling methods was applied to investigate these variations. Analysis shows that average porosities below 4000 m (〉13,123 ft) (vertical depth below sea floor) range from approximately 5% to as much as about 25% in comparable quartz arenitic sandstones. From porosity-depth trends, three porosity categories can be recognized (normal-, low-, and high-porosity sandstones). Normal-porosity sandstones fall along the regional average porosity-depth trend. Low-porosity sandstones have been subject to extensive quartz cementation as a consequence of a higher degree of thermal maturity and plot below the regional porosity-depth trend. High-porosity sandstones plot above the regional porosity-depth trend. Here, quartz cementation has been inhibited by grain-coating microquartz, and thus porosity has been preserved. Hydrocarbon emplacement has previously been thought to have inhibited quartz cementation in the study area, but this study concludes that the reservoirs are mainly water-wet, allowing for continued quartz cementation despite the presence of hydrocarbon pore fluids. Predicting the distribution of microquartz-coated sandstones and the degree of thermal maturity is therefore fundamental for successful exploration in the deeply buried parts of the synrift play. This study presents a regional and stratigraphic framework for such predictions that may be incorporated into play models in the area.

Description: The Livingstone Range anticlinorium (LRA) marks a major hanging-wall ramp where the Livingstone thrust cuts approximately 1000 m ([~]3281 ft) between regional decollement in the upper part of the Devonian Palliser Formation and the Jurassic Fernie Formation. Prethrusting and folding jasper {+/-} fluorite {+/-} sphalerite veins with halos of altered dolomitic host rock with high 87Sr/86Sr ratios (0.7094-0.7101) relative to most Paleozoic carbonate rocks (0.7081-0.7091) record percolation of fluids along basement faults that may also have contributed anomalously radiogenic strontium to diagenetically altered Paleozoic carbonate rocks throughout the Western Canada sedimentary basin. Fluid flow that occurred during thrust-propagation folding is recorded by dolomite {+/-} calcite veins, with{delta} 18O values that are similar to those of host rocks (-7.92 to -1.08{per thousand} Peedee belemnite). Anomalously high equilibrium temperatures (250 {+/-} 50{degrees}C) as determined by oxygen-isotope thermometry and slightly higher 87Sr/86Sr ratios relative to adjacent host rocks indicate that they formed from formation fluids and hot basement fluids in a rock-dominated system. Calcite veins with very low{delta} 18O values (-18 to -9{per thousand}) precipitated along faults that were active while the LRA was transported eastward by underlying thrust faults, uplifted, and rapidly cooled by infiltrating meteoric water. Thrusting created heating in the foreland basin ahead of the deformation because of the influx of thick insulating foreland basin sediments, causing thermal maturation of hydrocarbons. As thrusting deformation advanced through the rocks, infiltrating meteoric waters cooled the rocks and hydrocarbon maturation stopped. Structural traps accumulated hydrocarbons only if they were juxtaposed over both thermally favorable and hydrocarbon-favorable source rocks.

Description: Pleistocene fluvial, estuarine, marine, and deltaic depositional systems were identified in the uppermost 80 m (262 ft) of the central Gulf of Thailand modern continental shelf, situated approximately 70 m ([~]230 ft) below sea level. Integration of offshore three-dimensional (3-D) seismic reflection data, high-resolution shallow-penetration two-dimensional (2-D) seismic reflection sparker and boomer profiles, and shallow geotechnical borehole measurements enabled the identification of seven depositional sequences. The 3-D plan-view images at successive time slices exhibit single meandering channels (as much as 600 m [1969 ft] wide) and channel belts (as much as 10 km [6.2 mi] wide) deposited in the shelf during times of subaerial exposure. Additional geomorphic features imaged include incised valleys, interfluves, oxbow lakes, neck and chute cutoffs, and point-bar meander scrolls showing evidence of expansion and translation. The high-resolution 2-D profiles, with a tuning thickness of approximately 25 cm ([~]9.8 in.), enabled the discrimination of high-frequency stratigraphic discontinuities (sequence boundaries) and allowed a detailed bed-scale seismic facies characterization of fluvial (point bars), deltaic (clinoforms), estuarine, and marine deposits within a sequence-stratigraphic context. The complete succession shows that most fluvial systems lie within incised valleys in the lower parts of each depositional sequence, fluvial channels show a degradational stacking pattern, and no evidence of fluvial aggradation is observed; aggradation is limited to hemipelagic sedimentation during marine incursions. A shallow (

Description: With almost 200 coal-burning power plants in the region, the Ohio River Valley is an important region to evaluate potential formations for carbon dioxide (CO2) storage. In this study, we consider whether injection-induced stress changes affect the viability of the Rose Run Sandstone, considered as a potential effective storage unit. Our study uses a coupled geomechanical and reservoir simulator that couples fluid flow to induced stress and strain in all the significant stratigraphic units from the surface to the crystalline basement. The pressure and stress variations were modeled during CO2 injection, focusing on injection from a single well. The model uses a constant pressure condition on the boundary of the system. Both reservoir and surface deformation were simulated, and the possibility of reaching shear failure in the reservoir was tested. Carbon dioxide injection in the Rose Run Sandstone aquifer is not likely to cause any significant surface deformation. To consider the potential of increasing injectivity, simulation of a static fracture with a half-length of 300 m (984.3 ft) was considered. As the modeling shows that, with constant injection rate, the fracture can propagate beyond the propped length, a dynamic fracture propagation was also studied. This was achieved by allowing the fracture to grow as a function of a propagation criteria based on effective stress. Because of the favorable stress state of the Rose Run Sandstone, the propagation is primarily in the lateral direction, and no upward fracture propagation through the cap rock has been observed in the model. Finally, we demonstrate that dynamic fracture propagation significantly increases the possible injection rates, and its modeling is useful for determining optimal injection rates.

Description: A by-product of petroleum extraction, produced waters (PWs) containing selenium (Se), arsenic (As), and low-molecular-weight organics (LMWOs) may be generated. Pilot-scale constructed wetland treatment systems (CWTSs) were designed and built to evaluate the removal of these constituents from simulated fresh PW (SFPW). Study objectives were to characterize a fresh PW and determine the constituents of concern (COC); formulate an SFPW; design and build a pilot-scale CWTS for SFPW; and measure performance (i.e., COC removal rates and extents). The treatment goals for this study were to decrease Se concentration in SFPW from approximately 50 {micro}g/L to less than 5 {micro}g/L via microbial reduction; decrease As concentration in SFPW from approximately 20 {micro}g/L to less than 5 {micro}g/L via iron coprecipitation; and decrease LMWO concentration in SFPW from approximately 25 mg/L to less than 1 mg/L via biodegradation. To determine COC removal rates and extents and environmental factors, measurements included analysis of Se, As, LMWOs, dissolved oxygen, conductivity, pH, oxidation-reduction potential, alkalinity, hardness, and temperature. Mean outflow Se concentrations ranged from less than 1 to 47.1 {micro}g/L. Mean outflow As concentrations ranged from 5.7 to 9.5 {micro}g/L, and the mean outflow LMWO concentrations were less than 1 mg/L for all treatments and the untreated control. Organic carbon amendments had a significant effect on Se removal and no effect on As or LMWO removal. This pilot-scale study illustrates that CWTSs can enhance Se removal from SFPW and that removal can be achieved to meet stringent discharge limits. More research is needed to advance the techniques of As removal in CWTSs designed to simultaneously target Se.

Description: One method to beneficially use water produced from coalbed methane (CBM) extraction is subsurface drip irrigation (SDI) of croplands. In SDI systems, treated CBM water (injectate) is supplied to the soil at depth, with the purpose of preventing the buildup of detrimental salts near the surface. The technology is expanding within the Powder River Basin, but little research has been published on its environmental impacts. This article reports on initial results from tracking water and solutes from the injected CBM-produced waters at an SDI system in Johnson County, Wyoming. In the first year of SDI operation, soil moisture significantly increased in the SDI areas, but well water levels increased only modestly, suggesting that most of the water added was stored in the vadose zone or lost to evapotranspiration. The injectate has lower concentrations of most inorganic constituents relative to ambient groundwater at the site but exhibits a high sodium adsorption ratio. Changes in groundwater chemistry during the same period of SDI operation were small; the increase in groundwater-specific conductance relative to pre-SDI conditions was observed in a single well. Conversely, groundwater samples collected beneath another SDI field showed decreased concentrations of several constituents since the SDI operation. Groundwater-specific conductance at the 12 other wells showed no significant changes. Major controls on and compositional variability of groundwater, surface water, and soil water chemistry are discussed in detail. Findings from this research provide an understanding of water and salt dynamics associated with SDI systems using CBM-produced water.

Description: Using a process-based approach, a pilot-scale constructed wetland system was designed and built for treating water produced from an oil field in sub-Saharan Africa. The characteristics of the oil field-produced water were compared with water quality guidelines for irrigating crops and watering livestock to identify constituents of concern (COC) requiring treatment. The COC identified in the produced water include oil, grease, and metals (Zn, Ni, Fe, Mn). A pilot-scale constructed wetland treatment system was then designed and built based on biogeochemical pathways (i.e., sorption, oxidation, and reduction) for transferring and transforming the identified COC to achieve target concentrations meeting water quality guidelines. The pilot-scale treatment system consisted of three series of wetland cells, with four cells in each series. Two series of subsurface flow wetland cells were constructed with each cell having a two-layer hydrosoil of pea gravel and medium-size gravel planted with Phragmites australis. In addition, a series of free water surface wetland cells was constructed, with each cell containing sandy hydrosoil and planted with Typha latifolia. The design allows adjustment of parameters (i.e., hydraulic retention time and organic content of the hydrosoil) to promote the conditions needed to achieve treatment of COC through the identified biogeochemical pathways. This study provides an example of the design and construction of a pilot-scale wetland treatment system using a process-based approach.

Description: One of the many factors affecting the petroleum potential of thin-skinned thrust belts and their foreland plates is late orogenic normal, reverse, and strike-slip faulting, which occurs in the foreland plates and occasionally extends into the overlying thin-skinned thrust belts. This tectonism is typically active during the late stages of convergent orogeny, when subduction-driven thin-skinned thrusting ceases and the remaining convergence and geometric adjustment occur mainly within the foreland plate. The distribution, character, and orientation of particular structures generated during this collisional event, however, is to a great extent determined by the geometries of crustal blocks and orientations of preexisting faults and other weak zones within the foreland plates. As a result, despite the similar orogenic stress field, the dominant geometric expressions in various parts of the orogenic system may be different. Because massive petroleum generation and migration in both the thrust belt and in the foreland plate commonly occur later in the orogenic phase, late orogenic faulting can critically affect the whole petroleum system, including the generation, migration, and preservation of hydrocarbons. The potential existence of late orogenic tectonics should then be examined thoroughly, especially when exploring for petroleum at deeper structural levels of thrust belts and the underlying foreland plates. This is demonstrated by three examples from the Vienna Basin, Eastern Carpathians, and Dinarides-Hellenides, all parts of the European Alpine system. Several other examples, including the Rocky Mountain Laramide uplifts, the Eastern Cordillera in Colombia, and Timan-Pechora inverted structures in Russia, are mentioned to document the common occurrence of late orogenic faulting in orogenic systems.

Description: The material properties of sedimentary rocks are controlled by a range of parameters, including grain size, sorting, and modification of the original sediment through the diagenetic processes of compaction and cementation. To isolate the effects of diagenesis and explore how they modify permeability, we quantified changes in grain and pore morphology accompanying progressive diagenesis of a simple system: a well-sorted, variably quartz-cemented quartz arenite of relatively uniform grain size. The most common type of authigenic cement in sandstones, quartz overgrowths, is responsible for significant porosity and permeability reduction. The distribution of overgrowths is controlled by available pore space and the crystallographic orientations of individual quartz grains. We show that progressive quartz cementation modifies the grain framework in consistent, predictable ways. Detailed microstructural characterization and multiple regression analyses demonstrate that both the number and length of grain contacts increase as the number of pores increases and the number of large well-connected pores decreases with progressive diagenesis. The aforementioned changes progressively alter pore shape and reduce pore-size variability and bulk permeability. These systematic variations in the pore network correlate with changes in permeability, such that we can use our data to calibrate the Kozeny-Carmen relation, demonstrating that it is possible to refine predictions of permeability based on knowledge of the sedimentary system.

Description: This study is an investigation of aquitard characteristics and hydrocarbon entrapment in the Upper Devonian strata of the Bashaw area of Alberta, Canada. Oil and gas are trapped at two stratigraphic levels, the Leduc-aged Bashaw Reef Complex (D-3) and the Camrose Member-Nisku Formation (D-2), which are separated by a low-permeability aquitard of the Ireton Formation, a marl with variable carbonate content. The Ireton aquitard provides the principal control to cross-formational fluid flow in the area. Over much of the Bashaw Reef Complex, the Ireton aquitard ranges from approximately 25 m (~82 ft) thick to less than 1 m ( 32.8 ft) of Ireton aquitard. Where the overlying Ireton aquitard drape is less than 10 m (

Description: Terrestrial light detection and ranging (LIDAR) surveys offer potential enrichment of outcrop-based research efforts to characterize fracture networks and assess their impact on subsurface fluid flow. Here, we explore two methods to extract the three-dimensional (3-D) positions of natural fractures from a LIDAR survey collected at a roadcut through the Cretaceous Austin Chalk: (1) a manual method using the University of California, Davis, Keck Center for Active Visualization in the Earth Sciences and (2) a semiautomated method based on mean normal and Gaussian curvature surface classification. Each extraction method captures the characteristic frequencies and orientations of the primary fracture sets that we identified in the field, yet they extract secondary fracture sets with varying ability. After making assumptions regarding fracture lengths and apertures, the extracted fractures served as a basis to construct a discrete fracture network (DFN) that agrees with field observations and a priori knowledge of fracture network systems. Using this DFN, we performed flow simulations for two hypothetical scenarios: with and without secondary fracture sets. The results of these two scenarios indicate that for this particular fracture network, secondary fracture sets marginally impact ([~]10% change) the breakthrough time of water injected into an oil-filled reservoir. Our work provides a prototype workflow that links outcrop fracture observations to 3-D DFN model flow simulations using LIDAR data, an approach that offers some improvement over traditional field-based DFN constructions. In addition, the techniques we used to extract fractures may prove applicable to other outcrop studies with different research goals.

Description: Experimental modeling is used to study the geometry and evolution of structures and related secondary faults along releasing bends and offsets and restraining bends on strike-slip faults. The controls of the relative positions of adjacent strike-slip faults on the geometry of the structures and the difference in geometries between bends and offsets are investigated. A new method of laser scanning is used to map the geometry and evolution of the structures and related faults. The models show that oblique releasing bends connecting approaching faults result in spindle-shaped basins, whereas transverse bends result in more S-shaped or rhomboidal basins. Offsets result in the distribution of strain over a wider area and a larger number of faults compared with preexisting bends, which result in fewer well-defined basin-bounding faults. Secondary faults include R, R', and Y Riedel shears near the main strike-slip faults and oblique normal faults in the center of the basin. Fault patterns exhibit en echelon geometries with a progressive step down into the deepest parts of the basin. Symmetric, asymmetric, and double basins may form in any of the structural settings, depending on the slip distribution among faults on the basin margins. For restraining bends, oblique (45{degrees}) bends connecting approaching faults result in spindle-shaped uplifts, whereas transverse or oblique (135{degrees}) bends connecting overlapping faults result in more rhomboidal or rectangular uplifts. The fold trends are at increasingly higher angles with the strike faults for transverse and oblique (135{degrees}) bends. Secondary faults include en echelon reverse faults, which typically form along the steep limbs of asymmetric uplifts, normal faults, which are transverse or oblique to the axis of the structure, and R, R', and Y Riedel shears near the main strike-slip faults. The aspect ratios of the basins and uplifts increase with increasing displacement on the strike-slip faults. The results of these models can be used to interpret the structural and fault geometries in surface and subsurface structures formed along strike-slip faults.

Description: We undertake a multidisciplinary investigation into the distribution of asphalt in the Anacacho Limestone in an effort to decipher the potential roles of fractures and faults on secondary hydrocarbon migration. Field relationships between fractures, faults, and asphalt are evaluated at an asphaltic limestone mine near Uvalde, Texas. Based on their distributions, geometries, and structural relationships, we infer that normal faults provided vertical flow paths through the Anacacho Limestone, whereas strata-bound fractures enhanced lateral permeability. Variograms calculated from 75 subsurface measurements indicate that the asphalt concentration is anisotropically correlated and that the longest correlation length points in the mean strike direction of fractures and faults. A globally positioned laser rangefinder is used to measure faults and stratigraphic contacts within the mine. That data are then combined with lithologic descriptions from surrounding subsurface wells to construct a three-dimensional (3-D) model of the Anacacho Limestone. When an ordinary block-kriging algorithm populates the model with asphalt concentration estimates, the high values align along a trend that connects the two largest normal fault zones at the mine. The 3-D model provides a framework to numerically simulate secondary hydrocarbon migration. We test numerous hydrocarbon migration scenarios by adjusting simulation parameters within physically realistic ranges until producing an oil saturation field that agrees with asphalt concentration estimates. Our best match simulation indicates that oil entered the Anacacho Limestone through normal faults, that regional aquifer flow impacted oil flow, and that fractures increased the horizontal permeability of the formation by an order of magnitude along their strike direction.

Description: Vertical permeability is a critical parameter to estimate when modeling tidally influenced deltaic successions. The Campanian Sego Sandstone, in the Book Cliffs of Utah, is an outcrop analog for tidal systems with primary reservoirs being deposited as tidal bars in both confined and unconfined settings. A simple sand-shale model was used to quantify the effective vertical permeability using the shale character of the Sego Sandstone. Shale lengths, widths, thicknesses, and frequencies were measured from high-resolution light detection and ranging point clouds. Shales in confined tidal bars are approximately three times as long (mean, 16.3 m [53.5 ft]) and as wide (mean, 5.52 m [18.1 ft]). Within unconfined tidal bars, shales are roughly equidimensional (mean length, 18.6 m [61.0 ft]; mean width, 18.3 m [60.0 ft]). The different shale dimensions of confined and unconfined tidal bars result in different effective vertical permeability distributions, indicating that these two bar types behave differently under conditions of fluid flow. In analogous reservoirs, composed primarily of tidal bars, it is essential to differentiate and map confined and unconfined tidal environments.

Description: The J sandstone comprises less than 46 m (151 ft) of sandstone-dominated strata within the mudrock-dominated lower Upper Cretaceous succession of northwestern Nebraska. The unit is a prolific hydrocarbon producer in this region (Denver-Julesburg Basin), but its lithostratigraphic and sequence-stratigraphic framework, critical for reservoir characterization and mapping, is poorly known. We have achieved an improved understanding of depositional history and sequence stratigraphy by describing and correlating cores and wireline logs from wells within Sioux, Dawes, and Box Butte counties, Nebraska, and Niobrara and Goshen counties, Wyoming. Coals, paleosols, fluvial or inner estuarine sandstones, estuarine mudstones, fluvial conglomerate, shoreface sandstone, and reworked volcanic fallout (bentonite) lithofacies were identified. Trace fossil assemblages representing stressed expressions of the Skolithos and Cruziana ichnofacies are common. These lithofacies are arranged vertically into three erosionally based cycles, each less than 28 m (92 ft) thick, and each grade upward from fluvial or inner estuarine sandstones into estuarine mudstones and in turn into shoreface sandstones. The lateral and vertical stacking patterns of the lithofacies are complex, however, and the upper cycles appear to fill space eroded into the underlying ones. Northeast-southwest-elongate isochore trends appear in all three cycles. Lithofacies transition downdip from inner estuarine sandstones in the northeast to estuarine basin mudstones and shoreface sandstones toward the southwest. Detrital mineralogy indicates an easterly (cratonic) provenance for the entire unit. Our data suggest that the J sandstone in northwestern Nebraska accumulated in wave-dominated estuarine settings, as part of a long-lived transgressive systems tract. The unit as a whole occupies a complexly incised landscape cut during a third-order lowstand ca. 98 Ma. Coeval cycles of similar magnitude throughout the Western Interior suggest that the three cycles represent eustatic fluctuations. The highest quality reservoirs occur at the base of the unit in inner estuarine lithofacies in the central and southwestern parts of the study area.

Description: The Chezhen Basin has highly representative structural features of the Jiyang depression, Bohai Bay area. The structural geometry and the boundary fault linkage exert a strong influence on basin development and depositional environment. Based on structural analysis, at least six early fault segments are identified in the northern boundary of the Chezhen Basin. These fault segments are important in controlling stratal architecture and distribution. The antecedent structures controlled subbasin initiation and development. The Cenozoic rift initiated in the early Eocene with the development of six isolated fault segments associated with deposition of the Es4 member. During the deposition of the lower Es3 member, these six fault segments quickly linked and formed the present architecture frame. Fault linkage has not resulted in a redistribution of displacement. With the expansion of the Chezhen Basin, the depocenters of the upper strata were kept in nearly the same sites until the early Miocene, then the activity of the Chengnan fault ceased. Fault linkage is a significant event in basin evolution, and its process may be very rapid. However, the fault linkage exerted considerable control on sedimentation and evolution of the basin. This study demonstrates that it is necessary to integrate structural and stratigraphic data to reconstruct the temporal and spatial evolution of normal fault zones.

Description: A hydrostratigraphic model has been proposed based on the spatial distribution of aquitards, aquifers, aquicludes, recharge-discharge areas, salinity, mineralization, hydraulic head, diagenesis, and biodegradation information overlain with source rock potential, nature, and dispersal of hydrocarbons in the Mandapeta-Endamuru area, Krishna Godavari rift basin. This has resulted in understanding the verticolateral hydrodynamics and accumulation of gaseous hydrocarbons and variance in their geochemical properties. Three hydrogeologic systems are identified within the Mesozoic, and the associated gaseous hydrocarbons are characterized by their wetness and fingerprint Gastar diagrams. Temporal distribution of the salinity isolith in the vertical geologic column defines the intensity of meteoric infiltration and saline water percolation. In the Mandapeta subbasin, older formations are found to be less saline than the younger ones, indicating salinity inversion. Reservoirs of higher hydraulic heads are associated with gaseous hydrocarbons. The observed variation in hydraulic heads of the Mandapeta and Gollapalli aquifers is attributed possibly to the intervening Red bed aquitard acting as a seal. Areas of fault conduits are identified that facilitated the upward migration of hydrocarbons while allowing the percolation of infiltrated waters and further causing selective segregation of minerals. Vertical superimposition of different hydrogeologic systems and relative formation contacts also controlled the diffusion and nature of gaseous hydrocarbons. A composite hydrogeologic model has been framed based on studies for understanding the recharge-discharge dynamics incorporating seismic inputs.

Description: Mesozoic tectonic inversion in the Neuquen Basin of west-central Argentina was investigated by analyzing a three-dimensional seismic and borehole data set over prominent inversion structures related to transpressional tectonics along the Huincul arch. This conspicuous strike-slip deformation has been active since the Early Jurassic to Early Cretaceous and caused the reactivation of normal faults and the inversion of Triassic half grabens, some of which are imaged by the seismic data. Detailed structural and stratigraphic mapping allowed the identification of two main fault systems associated with inversion structures: (1) deep faults that affected basement and synrift strata where preexisting faults were selectively reactivated during inversion based on their length and (2) shallow faults that affected postrift and syninversion strata. Normal faults formed at high angle to the reactivated half-graben bounding fault as a result of hanging-wall expansion and internal deformation as it accommodated the shape of the curved footwall during oblique inversion. Structural restorations suggest that contraction during inversion was initially accommodated by folding and internal deformation of synrift sedimentary wedges, followed by displacement along half-graben bounding faults. We suspect that during late inversion, the weight of the overburden inhibited additional fault displacement and folding became the main shortening-accommodating mechanism. Natural examples described in this study exhibit significant along-strike variation in structural style and high structural complexity associated with relatively small amounts of inversion, which suggest the need for incorporating more complex deformation scenarios into analog models. Fault framework development and its linkage to a specific mechanism (e.g., hanging-wall deformation because of oblique inversion) enables the predictive analysis of subseismic faulting and fracture distribution, which can impact our understanding of the petroleum systems in the Neuquen Basin's northern embayment, especially regarding the significant fault development within the Cuyo Group, which may impact the Los Molles petroleum system.

Description: Primary basins form stratigraphically continuous successions on autochthonous salt and, therefore, in the northern Gulf of Mexico, contain all the components of a petroleum system (source, reservoir, trap, and seal). Most primary basins are encased entirely in salt or in some combination of salt and welds. Petroleum exploration in the deep-water Gulf of Mexico is currently focused on primary basin targets and increasingly those at their lateral boundaries. However, as these boundaries are commonly poorly imaged, robust structural models are critical to interpretation of their structural evolution and relative petroleum system risk. Using three-dimensional seismic data, we define three tectonostratigraphic provinces that characterize primary basin depocenters: (1) a disconnected salt-stock-canopy province in Mississippi Canyon; (2) an amalgamated salt-stock-canopy province in northern Atwater Valley, southeastern Green Canyon, Walker Ridge, and southern Keathley Canyon; and (3) a bucket-weld province in western Green Canyon, Garden Banks, and northern Keathley Canyon. We recognize six trap types in the primary basins: (1) autochthonous salt-cored folds, (2) turtle structures, (3) base-of-salt truncations, (4) salt feeders, (5) salt ridges, and (6) bucket welds. Most primary basin explorations to date have targeted traps in one of the first four styles. Future primary basin exploration will increasingly focus on the traps formed by bucket welds and salt-cored ridges. The contrasting evolution of these features has implications for reservoir continuity, charge access, and trap configuration. Of primary basin boundary trap types, salt feeders have the lowest petroleum system risk followed by bucket welds, with salt-cored ridges having the highest risk.

Description: Lithostratigraphic plays are one of the major targets for reserve growth in the nonmarine Songliao Basin, China. In this article, an integrated approach was adopted that applies principles and techniques of sequence stratigraphy and seismic sedimentology to the study of higher order sequences, depositional environments, and lithostratigraphic trapping styles. In the Sifangtuozi area, 20 higher order (fourth- or fifth-order) sequences in four third-order sequences were identified in an Upper Cretaceous interval using well and seismic data. Core description and wireline log classification helped identify distributary channel fill, distributary mouth bar, sheet sand, distal bar, prodelta/shallow lake, and semideep to deep lake deposits in fluvial-dominated deltaic systems. In two three-dimensional (3-D) seismic survey areas, seismic inversion and 90{degrees} phasing of seismic data converted seismic traces to pseudolithologic logs. Stratal slicing made it possible to interpolate and extrapolate well-data-derived sequence and facies interpretation to whole 3-D seismic surveys and then make broader interpretations and predictions on sand content, sandstone thickness, and geomorphological information. Play analysis using sandstone isopach or amplitude stratal slices and superimposed structural maps identified potential accumulations in small structural, lithostratigraphic, and combination traps. These traps are all significantly controlled by lithology, reservoir distribution, sealing conditions, and closure.

Description: Coalbed natural gas (CBNG) production typically requires the extraction of large volumes of water from target formations, thereby influencing any associated reservoir systems. We describe isotopic tracers that provide immediate data on the presence or absence of biogenic natural gas and the identify methane-containing reservoirs are hydrologically confined. Isotopes of dissolved inorganic carbon and strontium, along with water quality data, were used to characterize the CBNG reservoirs and hydrogeologic systems of Wyoming's Atlantic Rim. Water was analyzed from a stream, springs, and CBNG wells. Strontium isotopic composition and major ion geochemistry identify two groups of surface water samples. Muddy Creek and Mesaverde Group spring samples are Ca-Mg-SO 4-type water with higher 87Sr/ 86Sr, reflecting relatively young groundwater recharged from precipitation in the Sierra Madre. Groundwaters emitted from the Lewis Shale springs are Na-HCO 3-type waters with lower 87Sr/ 86Sr, reflecting sulfate reduction and more extensive water-rock interaction. To distinguish coalbed waters, methanogenically enriched [IMG]/medium/bltn09190-e118.gif" ALT="Formula "〉 was used from other natural waters. Enriched [IMG]/medium/bltn09190-e119.gif" ALT="Formula "〉, between -3.6 and +13.3{per thousand}, identified spring water that likely originates from Mesaverde coalbed reservoirs. Strongly positive [IMG]/medium/bltn09190-e120.gif" ALT="Formula "〉, between +12.6 and +22.8{per thousand}, identified those coalbed reservoirs that are confined, whereas lower [IMG]/medium/bltn09190-e121.gif" ALT="Formula "〉, between +0.0 and +9.9{per thousand}, identified wells within unconfined reservoir systems. These results demonstrate that [IMG]/medium/bltn09190-e122.gif" ALT="Formula "〉 analysis provides immediate data to help identify Atlantic Rim groundwater sources, hydraulic reservoir confinement, springs associated with methanogenic coalbed reservoirs, areas of peak methanogenic activity, and to help assess gas potential and promote efficient CBNG production.

Description: Two three-dimensional seismic data sets over the Albian western Golden Lane margin and time-equivalent basinal deposits of Poza Rica field allowed us to investigate the linked architecture of a steep-sided carbonate platform (El Abra Formation) and a thick accumulation of redeposited carbonate sediment at the toe of the slope and in the basinal area (Tamabra Formation). Regional seismic cross sections show that the most aggrading Albian platform has an eroded platform top, a scalloped margin, and a channelized slope that are equivalent to a 20-km (12.4-mi)-wide, westward-thinning, thick toe-of-slope apron made of chaotic, contorted, mounded, moderate- to high-amplitude reflections. Detailed reflection geometries in the Albian toe-of-slope and basinal deposits consist of chaotic to short, discontinuous, low-amplitude reflection at the toe of the slope of the Golden Lane platform, laterally changing to a discontinuous mounded, shingling reflection, which ultimately turns into high-amplitude parallel reflections. We interpret this lateral change to reflect the seismic signature of the change from the block- and debris-flow-dominated toe-of-slope area, to debris-flow and concentrated density flow deposits in the basin that ultimately grade laterally into pelagic deposits. On a flattened seismic slice, mounded reflections correspond to lobate to fan-shaped seismic events several kilometers wide that are interpreted as a carbonate basin-floor fan. Comparison between core and seismic data shows a dominance of debris flows in the lower two Albian sequences (Albian 1 and Albian 2) that grade vertically into more lobate concentrated density flows and turbidites in the upper two Albian sequences (Albian 3 and Albian 4). Seismic data used in this study, combined with core observations, do not support the interpretation of the Albian Tamabra Formation being of shallow-water origin. Seismic features identified as basin-floor fan, channel, and debris-flow deposits have a shape and size that are similar to those of other redeposited basinal carbonate deposits elsewhere. The seismic architecture shows that the Poza Rica field is a typical example of thick accumulation of grainy porous carbonate deposits in a basinal setting. This example shows the potential of a large hydrocarbon accumulation in a tectonically modified stratigraphic trap around shallow-water carbonate platforms.

Description: Existing classification schemes and models for clastic coastal depositional systems do not consider the potential amplifying or moderating effects of coastal morphology on depositional processes and do not provide a mechanism for the dynamic prediction of changes in coastal depositional style. A new process-based classification scheme based on the relative importance of primary, secondary, and tertiary processes is presented. This scheme permits a semiquantitative classification of clastic coastal depositional systems. In addition, it provides the basis for new models for clastic shorelines that convolve the effects of basin shape, coastal morphology, accommodation space, sediment supply, shoreline trajectory, and shelf width parameters on depositional processes. The end result is a marked improvement in the predictive capabilities of models. The models can describe and predict the likelihood of primary, secondary, and tertiary depositional processes acting in shoreline depositional environments via either a matrix or a decision tree approach. They are also dynamic in nature and can be applied to predict along-strike, updip, and downdip, or vertical changes in the dominance of depositional processes acting at any given location through geologic time. The key implications of these models are that given sets of known parameters, dominant and subordinate depositional processes or ranges of potential dominant and subordinate depositional processes acting at a coastline can be predicted. This provides an auditable methodology for determining reservoir modeling scenarios and reducing and managing the uncertainties in predictions of changes in clastic coastal depositional processes through time and space.

Description: We use the integration of gravity, magnetic, and 3-dimensional (3-D) seismic data to map sedimentary features and study the relationships between sedimentary and basement features in the Osage County area of northeast Oklahoma. The prominent gravity and magnetic anomaly studied within this region are related to the mid-continent rift system. However, we cannot substantiate this conclusion with geochronological age-dating data at this time. Prominent dipping Precambrian reflectors seen on seismic section suggest that extension occurred before emplacement of shallow basement. A regional episode of extension possibly occurred early in the development of the 1400 to 1340 Ma magmatic province. Thus, we interpret the structure we see to be a basin that might have formed during this interval. We use volumetric seismic attributes such as coherence and curvature derived from seismic data to better characterize subtle features such as collapse features and faulting and fracturing within the Mississippian and Ordovician carbonate deposits that are difficult to detect on conventional 3-D seismic data displays. Blended seismic images of these carbonate reservoirs reveal polygonal, highly coherent, and high-amplitude lineaments, which trend northeast and northwest. The northeast-striking lineaments are related to the late Paleozoic Nemaha tectonics, whereas the northwest lineaments are interpreted to be related to the inherent basement fabric or the draping of the Mississippian over a cockpit karst terrain. Although a one-to-one correlation between the basement structures and the carbonate reservoirs cannot be established, basement structure lineaments are parallel in orientation to those seen within the Mississippian chert and the Arbuckle Group.

Description: The Tarim Basin is the largest inland basin in China. The hydrocarbon charge history of the Silurian bituminous sandstone reservoirs in the Tazhong uplift was investigated using an integrated approach, combining detailed petrographic analysis (thin section, scanning electron microscopy, and transmission electron microscopy), clay mineral x-ray diffraction characterization, and modeling of authigenic clay minerals and subsequent potassium-argon (K-Ar) dating of authigenic illite. The timing of the hydrocarbon charges of the reservoirs in the Tazhong uplift area is compared with that of the Kongquehe area within the basin. The authigenic illite ages in the Tazhong uplift area and the Kongquehe area range from 383 Ma to 204 Ma, indicating a unique age distribution pattern in the basin. The Silurian oil accumulations were primarily formed in the late Caledonian through the late Hercynian. The reservoirs within wells Qiao-1, Kongque-1, Longkou-1, and Yingnan-2, located in the western area and the eastern area of the basin, were charged around 383 to 271 Ma in the late Caledonian to the early Hercynian. The reservoirs in wells Tazhong-37, Tazhong-67, Tazhong-12, and Tazhong-32, located in the center of the basin, were charged at around 235 to 204 Ma in the late Hercynian. A correlation between the authigenic illite ages and the thickness of the Silurian bituminous sandstones suggests that the paleostructural framework is a key controlling factor. The paleo-oil pool located in and around the sedimentary centers, such as wells Qiao-1 and Kongque-1, was formed relatively early (383 Ma). The K-Ar dating results were consistent with the results of conventional hydrocarbon accumulation history analysis and highlight the differences in the accumulation timing between various oil pools in different parts of the basin.

Description: Cretaceous low-accommodation deposits have been extensively studied in the subsurface of the Western Interior of North America because of their prolific hydrocarbon production and remaining potential. Understanding the stratigraphic complexities of these deposits in the subsurface relies strongly on detailed outcrop analogs. In this study, the Dakota Sandstone was examined along 100 km (62 mi) of semicontinuous outcrop between the towns of Hanksville and Ticaboo in the Henry Mountains of southeastern Utah. This region represented a low-accommodation setting located over the forebulge of the Cretaceous Western Interior Basin during accumulation of the unit. The Dakota Sandstone is 0 to 38 m (125 ft) thick, of Cenomanian age, and records multiple cycles of sediment accumulation. The Dakota Sandstone is subdivided into two condensed top-truncated stratigraphic sequences, the upper of which contains two parasequences. The basal parts of both sequences are composed of braided fluvial conglomerates and sandstone overlain by tidally influenced fluvial sandstone, inclined heterolithically stratified estuarine mudstone, carbonaceous shale, and coal. The overlying parasequences consist of coarsening-upward lower to upper shoreface mudstone, sandstone, tidal inlet deposits, and oyster shell concentrations. These facies define tripartite subdivisions of depositional environments typical of wave-dominated estuaries. The fluvial deposits may represent lowstand deposits, but overall sediments accumulated during transgressive systems tracts (TST). The parasequences recorded in the Henry Mountains are similar to the Dakota Sandstone of northwestern New Mexico and to high-frequency sequences identified in the Kaiparowits Plateau, approximately 80 km ([~]50 mi) to the southwest, which suggests eustatic driving mechanisms. The best potential for hydrocarbon reservoirs occurs in fluvial sandstones and conglomerates.

Description: A fluid inclusion study conducted on a well in the northern North Sea showed a remarkable correlation between fluid inclusion stratigraphy responses and depths of drilling bit changes. Further investigation of the well data suggested that extreme temperatures occasionally had been generated at the bit-sediment interface during drilling. Cracking of larger organic molecules to an abundance of smaller ones and trapping of these in inclusions formed by supercooling of partly melted sediment explain the correlation. Not all wells are consequently suitable for fluid inclusion screening analyses. Thus, before initiating fluid inclusion studies, wells that have experienced intense heat during drilling should be identified and avoided.

Description: Two-dimensional (2-D) modeling of source rock maturation and hydrocarbon (HC) generation histories were conducted for the Malay-Cho Thu Basin in the Gulf of Thailand and South China Sea. The source rocks comprise Oligocene synrift lacustrine mudstones and coals, postrift coals, and terrigenous-influenced mudstones. Three different lacustrine mudstone source rocks and coals were considered in the 2-D modeling, and each source rock was assigned specific generation potential and kinetics. Measured kinetics for bulk petroleum generation determined on two thermally immature upper Oligocene oil-prone lacustrine mudstones and on a terrigenous-influenced mudstone derived from wells were used together with published coal kinetics. The onshore Krong Pa graben, a small-scale rift basin in central Vietnam, was used as a conceptual model for the distribution of lithofacies, including source rock types, in the 2-D models. Exploration targets and drilled direct HC indicators (DHIs) are mainly located in the tectonically disturbed postrift succession. Modeling results suggest that the risks related to this play are (1) timing of petroleum generation from the oil-prone lacustrine synrift deposits relative to structural trap formation, (2) complex migration pathways through strongly faulted strata, and (3) relatively small kitchen areas. Oil generation from uppermost synrift and postrift coaly source rocks with minor contribution from lacustrine deposits after principal trap formation is consistent with the prominent terrigenous geochemical signature of oils in the Malay-Cho Thu Basin. A new untested play is proposed based on mapping of potential DHIs associated with sandstone bodies in tectonically undisturbed synrift traps.

Description: Fluviodeltaic stratigraphic architecture and its impact on fluid flow have been characterized using a high-resolution, three-dimensional, reservoir-scale model of an outcrop analog from the Upper Cretaceous Ferron Sandstone Member of central Utah. The model contains two parasequence sets (delta complexes), each with five or six parasequences, separated by an interval of coastal plain strata. Each parasequence contains one or two laterally offset teardrop-shaped delta lobes that are 6 to 12 km (4-7 mi) long, 3 to 9 km (2-6 mi) wide, 5 to 29 m (16-95 ft) thick, and have aspect ratios (width/length) of 0.4 to 0.8. Delta lobes have a wide range of azimuthal orientations (120{degrees}) around an overall east-northeastward progradation direction. In plan view, delta lobes in successive parasequences exhibit large (as much as 91{degrees}) clockwise and counterclockwise rotations in progradation direction, which are attributed to autogenic lobe switching. In cross-sectional view, parasequence stacking is strongly progradational, but a small component of aggradation or downstepping between parasequences reflects relative sea level fluctuations. We use flow simulations to characterize the impact of this heterogeneity on production in terms of the sweep efficiency, which is controlled by (1) the continuity, orientation, and permeability of channel-fill sand bodies; (2) the vertical permeability of distal delta-front heteroliths; (3) the direction of sweep relative to the orientation of channel-fill and delta-lobe sand bodies; and (4) well spacing. Distributary channel-fill sand bodies terminate at the apex of genetically related delta lobes and provide limited sand body connectivity. In contrast, fluvial channel-fill sand bodies cut into, and connect, multiple delta-lobe sand bodies. Low, but non-zero, vertical permeability within distal delta-front heteroliths also provides connectivity between successive delta-lobe sand bodies.

Description: The offshore Bohai Bay Basin, located in the central Bohai Bay Basin, north China, one of the most petroliferous basins in China. In this article, based on formation-testing temperature, drill-stem tests, and bottom-hole temperature data, 80 thermal gradient values at the depth interval of 0 to approximately 3000 m (~9843 ft) in the offshore Bohai Bay Basin were obtained. The basinwide average thermal gradient is 31.8 {+/-} 4.6{degrees}C/km. Based on the above thermal gradient data and the corresponding average weighted thermal conductivity data, 80 measured terrestrial heat flow values were obtained. These values range from 33.5 to 84.0 mW/m2, with an average value of 60.8 {+/-} 8.7 mW/m2. The heat flow and thermal gradient distribution in this region generally show higher values in the uplifts and lower ones in the sags. A thermal history, derived from vitrinite reflectance and apatite fission-track) data, indicates that Paleogene cooling occurred after a period of much higher paleogeothermal gradient (38[~]54{degrees}C/km). Tectonic subsidence analysis reveals that the area experienced initial synrift subsidence during the Paleogene followed by subsequent thermal subsidence since the Neogene. Thermal and tectonic subsidence histories of this area are of great significance to petroleum exploration and hydrocarbon resource assessment because they bear directly on issues of petroleum source rock maturation. The maturation and hydrocarbon expulsion histories of the Paleogene Shahejie 3 Formation (E2s3), which is the most important source rock in the offshore Bohai Bay Basin, are modeled. Results show that the Shahejie 3 Formation is in a high mature stage at the present day, and the Bozhong and Qikou sags are the most important kitchens. The Huanghekou sag became the third most important hydrocarbon kitchen in the early Neogene. Based on this hydrocarbon kitchen evolution, oil and gas mainly accumulated after 12 Ma. The evolution of kitchen areas may provide new insights for the understanding of the oil and gas exploration potential of the offshore Bohai Bay Basin.

Description: At Cranfield field, Mississippi, a monitored carbon dioxide (CO2) sequestration and enhanced oil recovery project provides a unique opportunity to study sealing properties of a marine shale as a CO2-confining zone. The reservoir is in the amalgamated fluvial basal sandstone of the lower Tuscaloosa Formation at depths of more than 3000 m (9843 ft). The marine mudstone of the middle Tuscaloosa forms a continuous regional confining system of approximately 75 m (246 ft). A 6-m (20-ft) core was retrieved from the middle Tuscaloosa marine mudstone approximately 70 m (230 ft) above the CO2 injection zone. We conducted a series of characterizing analyses on the core that would enable us to assess with high confidence seal performance over geologic time. The core displays considerable heterogeneity at centimeter to decimeter scales, with lithology varying from silt-bearing clay-rich mudstone to siltstone and very fine grained sandstone. In total, nine microfacies are recognized in the core. Petrographic, mineralogical, and chemical analyses (scanning electron microscopy, x-ray diffraction, and x-ray fluorescence) show that calcite cements preferentially form in coarser grained beds and have greatly reduced porosity and permeability, making silty and sandy beds less permeable than mudstone. Mercury intrusion capillary pressure tests show desirable sealing capacity for all samples capable of retaining a CO2 column of 49 to 237 m (161-778 ft) at 100% water saturation. Permeability and porosity of all facies are less than 0.0001 md and 4%, respectively. Pores in the samples are at nanometer scales, with modal pore-throat sizes less than 20 nm. Scanning electron microscopic imaging on ion-milled surfaces confirms that nanopores are scarce and generally isolated.

Description: Analysis of subsurface pressure data from Taranaki Basin using direct (e.g., repeat formation tester) and indirect measurements (drilling parameters and wireline log data such as sonic and resistivity) indicates the presence of three pressure zones: a near-hydrostatic regime (zone A) that extends across the entire basin and to varying depths; an underlying overpressured regime (zone B), with pressures approximately 1100 psi (7.584 MPa) above hydrostatic, that extends throughout the Manaia graben and north along the eastern basin margin at depths of 1900 to 4100 m (6234-13,451 ft); and a third regime (zone C), with approximately 2100 psi (14.479 MPa) overpressure, that directly underlies zone A and zone B in different parts of the basin (although well penetrations are limited). The primary cause of overpressure is interpreted to be disequilibrium compaction preserved in upper Eocene and Oligocene marine shales. In parts of the basin, hydrocarbon generation (and in particular cracking to gas at high maturities) is interpreted to contribute to overpressures. The overpressures drain laterally and vertically into permeable units. Intervening transition zones (seals) comprise lithologic boundaries, diagenetic zones, and fault planes. Oligocene carbonates, although commonly thin, provide an effective barrier to vertical hydraulic communication over much of the basin. The Manaia graben is a partially closed system, with overpressures retained by a complex combination of a top shale seal overlying a regional sequence boundary, lithologic barriers within fault compartments, fault planes, and subcropping sequences; episodic fault breach enables vertical transfer of fluids from zone B to zone A in a dynamic fault valve process. To date, all oil reserves have been found in zone A, a large proportion of gas-condensate reserves are within zone B, and no commercial reserves have been established within zone C. The spatial definition of these zones and the appropriate pressure regime is important for well design, drilling safety, determining hydrocarbon column heights and gas expansion factors, and for exploration migration analysis. Regional analysis of pressure regimes can identify subsurface barriers and seals. Faults, in particular, are key elements in fluid migration and the focusing of liquids at abrupt pressure transitions. The strength of fault planes and diagenetic zones is the likely control on dynamic fluid release. Zone C has been very lightly explored and may represent a potential for large dry-gas accumulations; the zone may be sealed by a diagenetic zone crosscutting lithologic boundaries (conventional mapping horizons).

Description: The electrical resistivity log has proven to be a powerful tool for lithology discrimination, correlation, porosity evaluation, hydrocarbon indication, and calculation of water saturation. Carbonate rocks develop a variety of pore types that can span several orders of magnitude in size and complexity. A link between the electrical resistivity and the carbonate pore structure has been inferred, although no detailed understanding of this relationship exists. Seventy-one plugs from outcrops and boreholes of carbonates from five different areas and ages were measured for electrical resistivity properties and quantitatively analyzed for pore structure using digital image analysis from thin sections. The analysis shows that in addition to porosity, the combined effect of microporosity, pore network complexity, pore size of the macropores, and absolute number of pores are all influential for the flow of electric charge. Samples with small pores and an intricate pore network have a low cementation factor, whereas samples with large pores and a simple pore network have high values for cementation factor. Samples with separate-vug porosity have the highest cementation factor. The results reveal that (1) in carbonate rocks, both pore structure and the absolute number of pores (and pore connections) seem more important in controlling the electrical resistivity, instead of the size of the pore throats, as suggested by previous modeling studies; (2) samples with high resistivity can have high permeability; large simple pores facilitate flow of fluid, but fewer numbers of pores limit the flow of electric charge; and (3) pore-structure characteristics can be estimated from electrical resistivity data and used to improve permeability estimates and refine calculations of water saturation.

Description: Analysis of more than 900 wireline logs indicates that the Middle Devonian Marcellus Formation encompasses two third-order transgressive-regressive (T-R) sequences, MSS1 and MSS2, in ascending order. Compositional elements of the Marcellus Formation crucial to the successful development of this emerging shale gas play, including quartz, clay, carbonate, pyrite, and organic carbon, vary predictably within the proposed sequence-stratigraphic framework. Thickness trends of Marcellus T-R sequences and lithostratigraphic units reflect the interplay of Acadian thrust-load-induced subsidence, short-term base-level fluctuations, and recurrent basement structures. Rapid thickening of both T-R sequences, especially MSS2, toward the northeastern region of the basin preserves a record of greater accommodation space and proximity to clastic sources early in the Acadian orogeny. However, local variations in T-R sequence thickness in the western, more distal, area of the basin may reflect the reactivation of inherited Eocambrian basement structures, including the Rome trough and northwest-striking cross-structural discontinuities, induced by Acadian plate convergence. Episodes of block displacement locally warped the basin into northeast-southwest-trending regions of starved sedimentation and/or erosion adjacent to depocenters in which regressive systems tract deposits were ponded. Block movement appears to have initiated in late Early Devonian time, resulting first in thinning and local erosion of the Oriskany sandstone in northwest Pennsylvania. This study, in addition to providing the basis for a predictive sequence-stratigraphic model that can be used to further Marcellus exploration, tells of a foreland basin more tectonically complex than accounted for by simple flexural models.

Description: Neogene siliceous rocks are known to act as both reservoirs and seals. However, the role of diagenetic alteration in the development of hydrocarbon reservoirs, seals, and traps in such formations is poorly understood. This study proposes two new models for hydrocarbon traps involving siliceous rock reservoirs with well-developed matrix porosity. The models are based on observations from the Yurihara and Toyotomi fields in Japan to evaluate changes in petrophysical properties associated with confining pressure and diagenetic transformations from opal-CT to quartz. When this diagenetic transformation boundary is located at depths greater than approximately 1000 m ([~]3300 ft), the overlying opal-CT porcelanite layer forms a seal and the underlying clay-poor quartzose porcelanite forms a reservoir, facilitating the development of a hydrocarbon trap. The quartzose porcelanite containing less than 6% Al2O3 (an indication of clay content) can act as a reservoir even 1000 m (3300 ft) below the boundary. When the boundary is located at depths shallower than approximately 500 m ([~]1650 ft), the overlying opal-CT porcelanite is unable to form a seal because of lower confining pressures--although clay-poor quartzose porcelanite continues to be a good reservoir. However, clay-rich quartzose porcelanite intercalated with the reservoir can act as a seal. When the quartzose porcelanite contains greater than 15% Al2O3, it has the potential to seal at the depth of the boundary. The requirement for a seal drops to greater than 8% Al2O3 at 1000 m (3300 ft) below the boundary. Such traps have not been reported outside Japan; therefore, these models are likely to be useful for hydrocarbon exploration in siliceous rock formations elsewhere, such as in the Monterey Formation of California.

Description: This study addressed the architecture and dimension distributions of fluvial deposits of the Olson Member of the Escanilla Formation through analysis of outcrops in the southern Buil syncline, Ainsa Basin, south central Pyrenees, Spain. The Olson Member consists of wide multistory channels alternating with mud-rich intervals composed of flood-plain deposits and "isolated" individual channels. Field descriptions and a combination of terrestrial light detection and ranging data and digital orthophotographs were used to map and document the abundance, distribution, and dimensions of sandstone bodies. These data show that channels are distributed according to the local stratigraphic framework and differential subsiding areas. Morphology (width, depth, and sinuosity) of the channels throughout the sequence evolve according to their stratigraphic position. During low-accommodation periods, channels stacked laterally, forming wide multistory channel belts. Under these conditions, single channels have a mean width-to-thickness (W:T) ratio of 49. During high-accommodation periods, single channels have a mean W:T ratio of 29. Moreover, the tendency of narrower and thicker channels having developed during high-accommodation periods is also clearly observable vertically from the base to the top of high-accommodation intervals throughout the sequence. This pattern of deposition results in increasing vertical connectivity, even in mud-rich high-accommodation periods. A geocellular three-dimensional model has been performed using object-based simulations. A succession of stochastic simulations was performed from the simplest one (random simulations) to more elaborated simulations, integrating successively outcrop observations. These simulations serve to image sandstone bodies' connectivity evolution according to outcrop observations and sedimentologic knowledge. Subsurface application of such vertical channel morphology evolutions and distribution could lead to more predictive flow-unit definitions and extensions.

Description: Structural elements of deformation-band fault zones are implemented as volumetrically expressed building blocks, that is, fault facies, in a series of synthetic reservoir geomodels and simulation models. The models are designed and built to reproduce a predefined range of fault system configuration, sedimentary facies configuration, and fault zone architecture. Using petrophysical properties derived from published field studies, the geomodel realizations are run in a reservoir simulator to monitor reservoir responses to variations in modeling factors. The modeled fault zones act as dual barrier-conduit systems, resulting in simulation models that can capture contrasting waterfront velocities, changes in waterfront geometries, and flow channelizing and bifurcation in the fault envelopes. The simulation models also show the development and sweep efficiency of bypassed oil and poorly swept regions because of the presence of the fault zones. Statistical analysis reveals that the fault facies modeling factors can be ranked according to impact on reservoir responses in the following descending order: fault core thickness, the type of displacement function, sedimentary facies configuration, the fraction of total fault throw accommodated by fault core and damage zones, fault system configuration, and maximum damage zone width. Fault core thickness is the most important factor because it governs the space available for fluid flow in the fault-dip direction. Other modeling factors affect the reservoir responses by controlling the geometry and continuity of fluid flow paths in the modeled fault zones.

Description: Because of their potentially large volumes and excellent reservoir properties, winglike clastic intrusion complexes may represent stand-alone exploration targets. However, determining the three-dimensional (3-D) geometry of such complexes is problematic because of limited exposure in the field and insufficient seismic resolution and well coverage in the subsurface. In this study, high-quality 3-D seismic reflection data from offshore Norway are used to determine the 3-D geometry of winglike intrusion complexes adjacent to a deep-water slope-channel complex. Intrusions form sheets or "wings" that are developed almost continuously along both margins of the 15-km (9-mi)-long channel complex. Intrusions dip up to 20{degrees} (more commonly

Description: Seismic images of Upper Jurassic organic-rich siliciclastic rocks are studied along the 2000-km (1243-mi) Norwegian margin. These rocks are considered the main source rock for most of the large oil and gas fields in the North Sea and Norwegian Sea. We report characteristic seismic expressions of thin-skinned gravitational gliding structures that are strata bound to the organic-rich formations. The most characteristic structures are listric faults that offset and rotate the upper part and sole out near the base of the organic-rich zone. These may be present in large areas (10,000 km2 [3861 mi2]), but are usually restricted to tilted areas. The strike of the faults was perpendicular to the downdip direction of the movement of mass, and fault directions can therefore be used as paleodip indicators. Several types of contraction structures are observed, and all are formed at a maximum of a few hundred meters of burial. Although they are not limited to organic-rich shales, such strata-bound structures may help identify organic-rich intervals in basins where their presence is unknown. We suggest that adding organic material to clay leads to reduced permeability. Compaction-related vertical fluid flow may cause fluid overpressure to build up at the base of a less permeable organic-rich layer during early burial. This high fluid pressure zone becomes a low-friction decollement surface on which overlying sediments slide to form characteristic thin-skinned deformation structures.

Description: Terrestrial laser scanning is used to capture the geometry of three single folded bedding surfaces. The resulting light detection and ranging (LIDAR) point clouds are filtered and smoothed to enable meshing and calculation of principal curvatures. Fracture traces, picked from the LIDAR data, are used to calculate fracture densities. The rich data sets produced by this method provide statistically robust estimates of spatial variations in fracture density across the fold surface. The digital nature of the data also allows resampling to derive fracture parameters that are more traditionally measured manually from outcrops (e.g., one-dimensional line transects of fracture spacing). The fracture statistics derived from the LIDAR data are compared with the calculated principal and Gaussian curvatures of the surface to assess whether areas of extreme curvature correlate with high-fracture density. For the folds studied, all the fracture spacing distributions showed an exponential distribution, and no significant correlation between fracture density and surface curvature was observed. This questions the validity of using curvature as a proxy for high brittle strains and highlights the need for a complete understanding of fold and fracture mechanics that include considerations of other factors including lithology, strain rate, and confining pressure, not just finite strain. The three case studies also illustrate how terrestrial laser scanning can be used to gather detailed quantitative data sets on fracture and fold distributions from outcrop analogs.

Description: Analysis of structural and sedimentologic data from onshore outcrops, offshore wells, and offshore seismic profiles indicates that the thrust belt geometry in eastern Bulgaria from the Paleocene to the Holocene is characterized by a southeastward plunge toward the western Black Sea Basin. This plunge was caused by (1) a combination of eastward-thinning continental crust in the west and oceanic crust in the east; (2) a postrift thermal subsidence of the continental crust; (3) buttressing and no buttressing of the Moesian platform against the thrust belt in its western and eastern parts, respectively; and (4) northeastward thrust belt advance. These factors controlled the overall eastward-diminishing uplift of the thrust belt and associated eastward sediment funneling into the Black Sea. Evidence for the eastward-fading uplift and buttressing includes the (1) eastward decreasing amount of shortening along constructed cross sections, yielding 30, 10.5, 11, and 4 km (18.6, 6.5, 6.8, and 2.5 mi, respectively) from west to east, respectively; (2) eastward trend of more complete stratigraphic sections and shallower erosional levels; and (3) eastward increase in decollement depths, being 3.7, 3.8, 9.5 to 13.5, and 12.3 to 14.1 km (2.3, 2.4, 5.9-8.4, and 7.6-8.8 mi). The age of the last thrusting is progressively younger toward the east from the middle Eocene through the late Eocene to the Oligocene from west to east, respectively. Onshore parts of the thrust belt, which were significantly affected by buttressing against the Moesian platform, exhibit thrusting followed by late Eocene gravitational collapse, Oligocene quiescence, and Neogene extension. The thrust belt part farther east exhibits thrusting followed by Oligocene-Neogene extension. A Paleocene-middle Eocene piggyback basin formed in the onshore part of the thrust belt, centered in the East Balkan zone, with a southeastward-plunging axis, which migrated northeastward with basin shortening and filling. The development of the East Balkan thrust belt and its later extensional modification had a dominant control over sediment transport, lithofacies, and depositional patterns. Developing thrust belt fold structures, together with the orogenic hinterland and highs in the foreland, formed a northeastward and eastward expanding system of sediment input. Southeastward-plunging axes of the foreland basin and the Paleocene-middle Eocene piggyback basin were the principal sediment transport pathways, together with subordinate internal synclinal axes. These depressions funneled sediments toward and into the western Black Sea Basin. As orogenesis advanced to the northeast, former depositional areas were uplifted and eroded, providing local sources of sediment.

Description: The main focus of this work is the investigation of the hydraulic function of faults, which is dependent upon the fluid-potential field, based mainly on theoretical considerations. The study displays the joint application of different research techniques, particularly hydrogeological methods for the western part of the Trans-Tisza region, Hungary, where thermal water and hydrocarbon accumulations are known. During the research, seismic, well-log, lithostratigraphic, and hydraulic data were analyzed to determine the hydrogeological framework and the fluid-potential field of the study area. As a result, the heterogeneity of a thick ([~]1000 m [[~]3281 ft]) and regionally extensive argillaceous aquitard unit was established, which is divided by structural elements and relatively thin (150-200 m [492-656 ft]) sandy aquifer units. Furthermore, two major strike-slip fault zones connecting the overpressured sub-Neogene basement with the uppermost aquifer unit and also intersecting each other were identified. Based on the complex investigation, we determined that the identified faults represent direction-dependent control over the fluid-flow systems of the study area. Both proved to act vertically as conduits but transversely as barriers; they enable pressure dissipation and intensive water upwelling from the sub-Neogene basement, resulting in a fluid-potential anomaly and, at the same time, in hydrocarbon entrapment. Consequently, during hydrocarbon exploration, it is not definitely necessary to search for low-permeability faults because high-permeability faults can also be acting as direction-dependent barriers for fluid flow. Moreover, the research also pointed out that hydrogeological methods are effective in hydrocarbon exploration during the evaluation of hydraulic function of faults.

Description: Experimental clay modeling is used to study the geometry and evolution of deformation zones formed above basement faults. The nature of deformation is compared for reverse faults dipping 30, 45, and 60{degrees}, vertical faults, and normal faults dipping 60 and 75{degrees}. Basement faulting results in the formation of a sheared triangular deformation zone that widens upward in the cover units. Most of the deformation is focused within a central zone of secondary faults, which propagate upward and eventually break through the entire section. Basal units exhibit steeper dips and higher fault densities, whereas stratigraphically higher units exhibit gentler dips and lower fault densities. The width of the deformation zone is generally greater for reverse faults with low dips. The anticlinal axial surface typically dips in the same direction as the synclinal axial surface for low- to moderate-angle reverse faults; however, the axial surfaces dip in opposite directions for vertical faults and normal faults. Particle paths suggest a convex upward rotation within the deformation zone, suggesting transfer of material across the extension of the master fault. Reverse faults are associated with secondary faults with reverse and thrust separations. Vertical faults are associated with mostly vertical and reverse secondary faults, whereas normal faults are generally associated with normal separation of most secondary faults. Therefore, the nature of secondary faults varies with structural position, possibly within the same layer. These results provide some key insights that are useful in the interpretation of macroscopic surface and subsurface basement-involved structures.

Description: We evaluated the pore volume available for a specific potential geologic carbon dioxide (CO2) storage site in the Upper Ordovician Queenston Formation near the AES Corporation Cayuga coal-fired power plant in Tompkins County, New York. Core data collected 25 mi (40 km) from the plant reveal that the Queenston Formation is a relatively homogeneous fine- to medium-grained sandstone with hematite cement. Seismic and core data indicate that the formation was deposited in a fluvial system with mobile channels and has thickness maxima that trend north-northwest. Porosity is a major factor affecting geologic CO2 storage potential, and it is important to understand discrepancies among porosity measured from core plug, neutron porosity, density-derived porosity, and thin-section point count values. Relative to core plug-derived porosity values, the neutron porosity log is more reliable than the electron density porosity values. Thin sections reveal that hematite cement is the primary factor affecting porosity variability. Seismic, core, and well-log data suggest that in a 25-mi2 (65-km2) area surrounding this power plant, the Queenston Formation can sequester 18 million metric tons ({+/-}11 million metric tons) of CO2 emission from the Cayuga power plant ([~]8 yr of CO2 output, with a range of 3-12 yr), although many uncertainties must be better constrained to obtain a more accurate estimate. Because the Queenston Formation near the Cayuga power plant is relatively homogeneous, most of the formation at this location offers the potential for CO2 storage in its pore space.

Description: A growing concern that increasing levels of greenhouse gases in the atmosphere are contributing to global climate change has led to a search for economical and environmentally sound ways to reduce carbon dioxide (CO2) emissions. One promising approach is CO2 capture and permanent storage in deep geologic formations, such as depleted oil and gas reservoirs, unminable coal seams, and deep brine-containing (saline) formations. However, successful implementation of geologic storage projects will require robust monitoring, verification, and accounting (MVA) tools. This article deals with all aspects of MVA activities associated with such geologic CO2 storage projects, including site characterization, CO2 plume tracking, CO2 flow rate and injection pressure monitoring, leak detection, cap-rock integrity analysis, and long-term postinjection monitoring. Improved detailed decision tree diagrams are presented covering the five stages of a geologic storage project. These diagrams provide guidance from the point of site selection through construction and operations to closure and postclosure monitoring. Monitoring, verification, and accounting techniques (both well-established and promising new developments) appropriate for various project stages are discussed. Accomplishments of the Department of Energy (DOE) Regional Carbon Sequestration Partnerships field projects serve as examples of the development and application to geologic storage of MVA tools, such as two-dimensional and three-dimensional seismic and microseismic, as well as the testing of new cost-effective monitoring technologies. Although it is important that MVA and computer simulation efforts be carefully integrated to ensure long-term success of geologic storage projects, this article is limited to a discussion of MVA activities. This article is an extension of a report published in 2009 by the DOE National Energy Technology Laboratory titled, "Best Practices for Monitoring, Verification, and Accounting of CO2 Stored in Deep Geologic Formations," to which interested readers are referred for more details on MVA tools. Ultimately, a robust MVA program will be critical for establishing carbon capture and storage as a viable greenhouse gas mitigation strategy.

Description: Many published sequence-stratigraphic frameworks lack a systematic and consistent designation for both depositional sequences and key surfaces, despite the original goal to provide a fully integrated stratigraphic architecture, including diagnostic age information. Based on a system in use for more than 10 yr at ExxonMobil, we recommend methodologies for a chronostratigraphic designation system (CDS) using more uniform and robust sequence-stratigraphic designations. After objectively defining important physical stratigraphic surfaces, biostratigraphic and other age-constraining information is used to designate surfaces and the packages of rocks they bound. This leads to the establishment of a sequence chronostratigraphic framework for a local area of investigation (outcrop section, field, region, or basin). Only after demonstrating clear well-documented ties to Phanerozoic global coastal onlaps or cycle charts are these sequences and associated surfaces considered as "global" entities and designated as such. Higher frequency sequences and surfaces are also accommodated in this CDS. Alternative designations for areas with limited or poor quality chronostratigraphic information are also discussed. The CDS has proven to have great use in all Phanerozoic strata, different tectonic settings, and depositional environments, especially when chronostratigraphic age constraints are robust. We have used this system at regional and basinal scales in many geographic locations to help reduce uncertainty in identifying and correlating reservoirs, sources, and seal rocks. Predicting the local distribution and quality of reservoirs as well as seals within a producing field and near field wildcats is also facilitated by this system. This system has demonstrated use in the correlation of outcrop sections within a basin or between basins. Rigorous use of the CDS proposed here will permit meaningful regional and/or interbasinal correlation that is difficult to carry out with the diverse systems currently in use. This uniform designation scheme will also facilitate communication within a company and between institutions, as well as among academic investigators.

Description: The bitumen of the Lower Cretaceous McMurray Formation in Alberta arguably represents one of the most important hydrocarbon accumulations in the world. In-situ development relies on heat transfer through the reservoir via horizontal steam injection wells placed 4 to 6 m (13-20 ft) above horizontal producers near the base of the sandstone reservoirs. Given this technology, understanding the distribution of the resource is paramount for a successful development program. Sedimentary facies provide a direct control on bitumen distribution and recovery. Most facies models developed to describe and predict sedimentary units of the McMurray Formation consider fluvial, estuarine, and/or deltaic depositional settings. In-situ development, however, requires a particularly high-resolution sedimentologic interpretation. High-quality three-dimensional seismic reflection data and extensive drill cores from acreage located approximately 50 km (31 mi) south of Fort McMurray provide important insights into the sedimentologic organization of reservoir and nonreservoir deposits in the upper one third (40 m [131 ft]) of the reservoir interval. Geomorphologic characteristics of the strata observed in seismic time slices reveal that a fluvial depositional setting was prevalent. Ichnologic and palynologic data, as well as sedimentary structures suggestive of tidal processes, indicate a marine influence in the upper reaches of a fluvial system characterized by channels that were 390 to 640 m (1280-2100 ft) wide and 28 to 36 m (92-118 ft) deep. The complex stratigraphic architecture consists of a mosaic of large-scale depositional elements, including abandoned channels or oxbow lake fills, point bars associated with lateral accretion, point bars associated with downstream accretion, counter point bars, and sandstone-filled channels. Reservoir deposits are primarily associated with point bars and sandstone-filled channels.

Description: This study addresses the field-scale architecture and static connectivity of fluvial sandstones of the lower Williams Fork Formation through analysis and reservoir modeling of analogous outcrop data from Coal Canyon, Piceance Basin, Colorado. The Upper Cretaceous lower Williams Fork Formation is a relatively low net-to-gross ratio (commonly

Description: The Moxizhuang field is a small oil field in the central Junggar Basin containing several low-saturation, low-resistivity oil reservoirs, which display a complex correlation between oil saturation and porosity and permeability that is atypical of both the filled and drained reservoirs. Biomarker associations of crude oil and grains containing oil inclusions (GOIs) of both the present-day water-bearing zones (water zones) and the oil- and water-bearing zones (low-oil-saturation pay zones) were analyzed to investigate the mechanisms for the formation of the low-saturation, low-resistivity oil accumulations. The biomarker assemblage and hierarchical cluster analysis indicate that oil in the Moxizhuang field was mostly generated from Permian source rock deposited in brackish to hypersaline anoxic environments. The pay zones and several water zones display GOI values as much as 38%, greater than the generally accepted threshold GOI value for an oil column (5%). These GOI values are similar to those for high-saturation oil reservoirs in the Bohai Bay Basin and oil zone samples from Australian basins, suggesting that both pay zones and water zones were high-saturation oil reservoirs in the geologic past. Geologic history analysis shows that the Moxizhuang field was located on the north wing of a paleoanticline during oil charge in the Late Cretaceous to Paleogene. This anticline has gradually evolved into a south-dipping monocline since the Neogene, causing northward remigration of accumulated oil. Differential lateral leakage of accumulated oil in different sandstone layers during the remigration phase led to the formation of the water zones with high GOI values (completely drained reservoirs) and the low-saturation, low-resistivity pay zones (partially preserved reservoirs) and caused the complex correlation between oil saturation and porosity and permeability. Compared with other postaccumulation physicochemical alteration processes, lateral leakage has rarely been recognized. Recognizing differential lateral leakage of accumulated petroleum with the existence of high-quality unfaulted cap rocks has important implication for petroleum exploration in sedimentary basins having complex evolution histories.

Description: Analysis of three-dimensional seismic data from the lower Congo Basin, offshore Angola, reveals numerous fluid-flow features in the Miocene to Holocene succession and the potential for large, shielded traps underneath basinward overhanging salt structures. The fluid-flow evidence includes present-day sea floor pockmarks clustered above salt structures, Pliocene-Pleistocene stacked paleopockmarks and Miocene pockmark fields. Other fluid-flow features include high-amplitude cylindrical pipe structures 60 to 300 m (197-984 ft) wide and 25 to 300 m (82-984 ft) high within lower and middle Miocene strata, thick ( 1 km [0.6 mi] beneath the sea floor). The Miocene pockmark fields occur at a specific horizon, suggesting a regional fluid expulsion event at ca. 12 Ma, and the Miocene fluid-flow regime is interpreted to be dominated by thermogenic fluids supplied via carrier beds and leaking vertically above structural highs. The Pliocene-Pleistocene fluid-flow regime was dominated by short-distance vertical fluid migration and expulsion related to early stage diagenetic processes involving biogenic methane and pore water. The present-day fluid-flow regime is inferred to be dominated by thermogenic fluids primarily controlled by kilometer-scale salt-flank-controlled migration. The study emphasizes the use of seismically imaged fluid-flow features in hydrocarbon systems analysis by documenting the evolution of an overburden plumbing system through time, involving several fluid types and flow regimes, depending on the spatiotemporal availability of thermogenic and diagenetic fluids and the tectonostratigraphic occurrence of aquifers, traps, and seals.

Description: The use of remote sensing data increases the efficiency of field mapping, especially in areas with difficult access or where geologic fieldwork is expensive or hazardous. This study presents a newly developed software tool for interactively mapping and measuring the spatial orientation (i.e., dip angle and dip direction) of finite planar geologic structure from digital elevation models (DEMs). The orientations of planar data (e.g., sedimentary bedding or fault planes) are derived by approximating a virtual plane to the intersection of the planar feature with the DEM topography. To increase the informative value of the DEM, satellite images can be draped onto the topographic data set. The software tool was tested in the Zagros fold and thrust belt, northeast of Erbil (Kurdistan, northeast Iraq), where the stratigraphy has been deformed into subcylindrical fold trains. Computed orientations have been compared with actual dip angles and directions measured in the field. Under favorable conditions (moderately dipping planes, strong competence contrast between stratigraphic boundaries, intersection with a rugged topography, low vegetation), statistical comparison of computed data with the field measurements demonstrates that the spatial data set can be reproduced from the DEM within an average error of approximately 10{degrees}. The strength of the method is demonstrated by integrating field data with computed values from inaccessible areas, resulting in a reasonably well-constrained balanced geologic cross section.

Description: Carriers are important links between sources and traps for hydrocarbon migration and accumulation in a petroleum system. Oil and gas commonly migrate along narrow and irregular pathways in porous media, even in macroscopically homogeneous media. A migration simulator based on the invasion-percolation theory, which couples the buoyancy of a hydrocarbon column as the driving force with capillary pressure as the resisting force, satisfactorily explains migration processes in heterogeneous media. In macroscopically homogeneous carriers, migration pathways are generally perpendicular to equipotential lines, but locally, the pathways can be irregular because of the influence of microscopic heterogeneity. The degree of irregularity of these pathways depends on the difference between competing driving and resisting forces. When numerous pathways form in a migration-accumulation system, the flux of migrating hydrocarbons may vary among these pathways. In macroscopically heterogeneous carriers, the irregularity of migration pathways is exacerbated. When the driving force is relatively weak, hydrocarbons tend to migrate in carriers where the hydraulic conductivity is relatively large. These pathways differ from those predicted only on the basis of flow potential. Simulation of the migration process in the Middle Jurassic carrier beds of the Paris Basin demonstrates the characteristics of the migration simulator in the analysis of migration pathway heterogeneity. Results are comparable to or superior to those achieved with previous simulation approaches.

Description: A continuum-based pore-scale representation of a dolomite reservoir rock is presented, containing several orders of magnitude in pore sizes within a single rock model. The macroscale rock fabric from a low-resolution x-ray microtomogram was combined with microscale information gathered from high-resolution two-dimensional electron microscope images. The low-resolution x-ray microtomogram was segmented into six separate rock phases in terms of mineralogy, matrix appearances, and open- versus crystal-filled molds. These large-scale rock phases were decorated (modeled) with geometric objects, such as different dolomite crystal types and anhydrite, according to the high-resolution information gathered from the electron microscope images. This procedure resulted in an approximate three-dimensional representation of the diagenetically transformed rock sample with respect to dolomite crystal sizes, porosity, appearance, and volume of different matrix phases and pore/matrix/cement ratio. The resulting rock model contains a pore-size distribution ranging from moldic macropores (several hundred micrometers in diameter) down to mudstone micropores (

Description: Geochemical characteristics of hydrocarbons from the South Liberty field, Liberty County, Texas, were integrated with local stratigraphy, pressure, temperature, seismic data, and formation water chemistry to determine the source, maturity, and migration pathways of hydrocarbons associated with the salt dome in the southeast Texas Gulf Coast. Fourteen crude oil samples from the soft-geopressured Cook Mountain and Yegua (both Eocene) and Frio (Oligocene) reservoirs (989-2886 m [3245-9469 ft]) were analyzed by whole-oil high-resolution gas chromatography (GC) and GC-mass spectrometry. Pressure and temperature data from 36 wells were used to model the thermal maturation history in the vicinity of the dome. South Liberty oils were found to belong to a single genetic family, sourced from rocks with a similar level of maturity. Biomarkers indicate they were formed in a marginal marine environment with notable terrestrial input from a likely lower Tertiary source rock (probably the downdip lower Claiborne and/or Wilcox Group). Oils were generated within the peak oil window (vitrinite reflectance, ~0.6-0.9%) at expulsion temperatures of 125 to 130{degrees}C. Thermal modeling indicates the lower Claiborne and/or upper Wilcox beds attained optimum maturity in and around the dome between 8 to 20 Ma and 18 to 31 Ma, respectively. Oil migration toward the structure probably occurred through faults breaching the deep-seated lower Claiborne/upper Wilcox source. Two severely biodegraded samples were found, and these were associated with cooler formation water (50 to 55{degrees}C) with a greater meteoric water component (48-60%). Comparison with Brazoria County oils (100 km [62 mi] to the southwest) indicates that the South Liberty oils belong to the same genetic family, with minor differences resulting from a greater input from terrestrial kerogen.

Description: Basin to mid-ramp cyclic facies of the Tithonian Vaca Muerta Formation are exposed in the Loncoche Creek section of the Neuquen Basin, Mendoza province, Argentina. This unit is characterized by a decimeter-scale rhythmic alternation of marls, shales and limestones and extends from the lower Tithonian to the upper Berriasian. Cyclostratigraphic studies based on a detailed facies analysis allowed the identification of cyclic patterns with frequencies within the Milankovitch band. According to biostratigraphic data, the dominant cycle in the studied section has a period of 20 k.y., which correlates with the Earth's axis precession element. Spectral analysis based on a series of compacted and decompacted cycle thickness identified a subordinate frequency of about 90 to 120 k.y., which we interpret as the modulation of the precessional cycle caused by the Earth's orbital eccentricity. The strength of the precession signal, together with the absence of a well-defined cyclicity attributable to the obliquity orbital cycle (i.e., [~]40 k.y.), is in agreement with previous data from the Northern Hemisphere.

Description: The sequence-stratigraphic framework and depositional systems of an Oligocene lacustrine rift succession in the Liaozhong depression of Bohai Bay Basin in northeastern China were investigated using seismic profiles, complemented by well logs and cores. Seven sequences are identified on the basis of unconformities on basin margins and correlative conformities in the basin center. Depositional systems are associated with systems tracts within sequences. Lowstand systems tracts are dominated by sublacustrine fans; transgressive systems tracts are mainly composed of beach-bar deposits; and highstand systems tracts are characterized by deep lacustrine fan or braid-delta deposits. Episodic tectonic movement was the principal factor that controlled the development of the sequences. Lake-level changes resulting from climatic oscillations may have controlled the development of these sequences. The balance between tectonic subsidence and sediment supply controlled the type of lake basin. The Bohai Bay Basin was a balanced-fill basin in the early and middle stages of the Dongying Formation and evolved into an overfilled basin at the end of deposition of the Dongying Formation. This study enhances the understanding of depositional system configuration and systems tracts in a typical rift basin and proposes that the most favorable sandstone reservoirs are developed in sublacustrine fan deposits. Relative lowstand sublacustrine fan deposits capped by relative highstand prodelta or deep lacustrine mudstones form the highest potential lithostratigraphic traps.

Description: The late Miocene Urenui Formation cropping out on the eastern margin of Taranaki Basin, currently New Zealand's only commercially exploited hydrocarbon basin, is dominated by siliciclastic slope mudstone ( 33 ft) long and 5 to 70 cm (2 to 28 in.) across, these concretions formed from the precipitation of fine-grained calcite or dolomite cement within siliciclastic mud in the shallow subsurface (likely

Description: The Permian Basin of west Texas and New Mexico is the largest petroleum-producing basin in the United States. In this area, multiple episodes of Paleozoic faulting, uplift, and erosion occurred, including those events related to the Marathon-Ouachita orogeny (Hercynian orogenic cycle [~]350-250 Ma). Within Paleozoic rocks in the Permian Basin, the Pennsylvanian succession is the second most oil-productive system, next to the Permian. This succession has been viewed historically as sedimentologically and stratigraphically complex because of the interplay of deposition, coinciding with icehouse climatic conditions during a second-order global transgression, and presumed active tectonism. New paleodepositional systems maps for the Morrowan, Atokan, Desmoinesian, Missourian, and Virgilian stages of the greater Permian Basin are presented. This study integrates varied data, including outcrop, drill core, geophysical (seismic and gravity), wireline log, biostratigraphic, and reservoir quality. Systems maps depict the spatial and temporal distribution of sediment source areas, shallow-water to basinal carbonates, alluvial to open-marine siliciclastics, shales, and areas of uplift. A Pennsylvanian reservoir architecture and facies evolution diagram combines data on key reservoir facies and targets, including their dimensions; the relative location of the facies tracts within each depositional system; the overall system architecture; and each stage's potential for diagenetic modification. A unified depositional system model provides continuity between the paleodepositional systems maps and summarizes the entire Pennsylvanian facies proportion evolution within eight provinces of the Permian Basin. The depositional systems information is referenced to second- to fourth-order eustasy curves and tectonic input. The reservoir evolution diagram and paleodepositional maps used in conjunction with the unified systems model provide the reader with the most current and extensive integration of data on the Pennsylvanian geologic history in the greater Permian Basin from a sedimentologic and petroleum reservoir systems perspective. Insights into facies distribution, the overall development of the basin and its subbasins, tectonic episodes, identification of potential new play types and exploration targets, and new depositional and sequence-stratigraphic architectural models are presented in this article.

Description: Recent studies of shelf-margin deltas in the Gulf of Mexico lack three-dimensional (3-D) seismic interpretation that allows prediction of lithology distribution, deformation features, and overall reservoir heterogeneity, and only a few 3-D studies of shelf-margin deltas in other parts of the world exist. This paper examines the 3-D geomorphology and internal facies architecture within a sequence-stratigraphic framework of a shelf-margin delta in a salt dome minibasin, within the Gulf of Mexico, offshore Louisiana, using 3-D seismic data. The 3-D data also allow an evaluation of the potential pathways for sediment bypass from delta front to slope and deep-water depositional environments. The delta consists of a series of offlapping sandy clinoforms, interpreted as being associated with a prolonged forced regression and ensuing lowstand of eustatic sea level, related to oxygen isotope stage 6, which lasted for about 45 k.y. The lowstand delta is onlapped by a transgressive mud wedge and is underlain and capped by regionally persistent highstand mudstones. The central part of the delta shows intradeltaic syndepositional growth faults, likely triggered by deposition of heavy delta-front sands over mobile prodeltaic muds, reflecting the river-dominated nature of the delta. A postdepositional shallow-water mass transport complex (MTC), which moved almost perpendicular to the direction of the regional delta progradation, remobilizes the deltaic deposits. The MTC was likely induced by uplift of the adjacent western salt dome. We hypothesize that the high degree of syndepositional and postdepositional deformation is related to the prolonged nature of the eustatic lowstand, as well as the salt tectonics. Tributive submarine slope channels form downdip of the delta front and may also reflect incision during the prolonged eustatic lowstand. The salt tectonics caused focusing of the dispersed delta-front sediments, mostly originating from terminal distributary channels, into the convergent tributive slope-channel system. Although this is an unstable supply-dominated shelf-margin delta, the salt tectonics likely prevented the delta from avulsing once it reached the shelf edge and also caused the focusing of dispersed sediment effectively into a point source for delivery to deep-water systems. This contrasts with less confined high-sediment supply delta systems farther along the coast, which lack linked submarine deposits because they reach the shelf margin before maximum eustatic lowstand and avulse before building significant deep-water systems.

Description: The Susquehanna River Basin drains 27,510 mi2 (71,251 km2), covering parts of New York, Pennsylvania, and Maryland, and provides 50% of the freshwater inflow to the Chesapeake Bay. The Susquehanna River Basin Commission (SRBC) is a federal-interstate compact agency regulating surface and groundwater withdrawals, diversions, and consumptive uses of water, including those associated with natural gas development. Although specific black gas-bearing shale formations are already identified, including the Marcellus, Utica, Antes, Burket, Geneseo, Mandata, Middlesex, Needmore, and Rhinestreet, the SRBC regulatory activity is applicable to any and all gas-bearing formations (Figure 1). The SRBC does not regulate wastewater discharges or pollution incidents because these are already regulated by member jurisdictions of SRBC. As a water resource...

Description: The Ohio River Valley Water Sanitation Commission (ORSANCO) is an interstate compact water pollution control commission created jointly in 1948 by eight states (Indiana, Illinois, Kentucky, New York, Ohio, Pennsylvania, Virginia, and West Virginia) with the approval of the U.S. Congress (Figure 1). The mission of ORSANCO, as provided in the Ohio River Valley Water Sanitation Compact, is to regulate activities in the rivers, streams, and waters of the Compact district (i.e., the Ohio River Basin as it exists within the eight signatory states) to mitigate existing and future surface water pollution. The Ohio River is an important natural resource in many regards. Along its 981-mi (1579-km) length, it provides habitat for more than 120 species of fish and facilitates the transport of 200+ million tons of goods per year. In addition, more than 5 million people rely on the Ohio River as their drinking water supply. The Ohio River Valley Water Sanitation Commission, in consonance with its mission and the broad powers granted to it under the Compact, operates programs to improve surface water quality in the Ohio River and its tributaries, such as the...

Description: Pennsylvania is not only the birthplace of the modern petroleum industry but also the focus of the modern Marcellus Shale gas play. For more than 150 yr, Pennsylvania has experienced a rich history of oil and gas exploration and production, witnessed the advent of modern petroleum regulations, and now sits deep in the heart of the largest domestic shale gas play the United States has ever seen. Although a known source rock for decades, the Marcellus Shale was not considered a viable gas reservoir until Range Resources Corporation (Range) discovered the play with its completion of the Renz No. 1 well in Washington County in October 2004. Using horizontal drilling and hydraulic fracturing techniques used by operators working the Barnett Shale gas play, Range has gone on to complete hundreds of horizontal shale gas wells in Washington County alone. Other operators have followed suit in counties from one corner of the state to the other, and as of June 2011, the Commonwealth has issued nearly 6500 Marcellus Shale gas well permits. Based on publicly reported well completion and production data, an average Marcellus Shale gas well requires 2.9 million gal of water during the hydraulic fracturing process and produces 1.3 mmcf gas/day. Furthermore, the U.S. Energy Information Administration has estimated that as of mid-2011, daily Marcellus Shale gas production in Pennsylvania exceeds 2.8 bcf. Because of the level of drilling activity and production associated with the Marcellus play, Pennsylvania has become the nexus of shale gas production and water management issues.

Description: Upper Jurassic to Lower Cretaceous synrift sandstones from two industry exploratory wells in the Flemish Pass Basin were studied for provenance using heavy mineral proxies. These sandstones were deposited during the North Atlantic rifting stage, at which time rifting intensified between Iberia and the Grand Banks. Several heavy mineral methods were used, including in-situ U-Pb geochronology and morphological and chemical analysis of detrital zircons, chemical discrimination of detrital tourmalines, and heavy mineral ratios. Clastic bed-load material entering the northern Flemish Pass Basin during the Tithonian to Berriasian was connected to transport systems reaching west, as far as 400 to 500 km (249-311 mi). Source areas to the west included igneous rocks and associated cover sequences of the Avalon zone, as well as the magmatic rocks, metasedimentary rocks, and associated cover sequences present in the Central mobile belt. The eastward-directed input of bed-load material into the basin is considered to have resulted in the concentration of sandstone units along its western margin, with deteriorating reservoir grade toward the east. Given the regional extent of drainage systems, it is likely that similar constraints apply to equivalent sandstones in the adjacent East Orphan Basin. By the Valanginian-Barremian, paleodrainage orientations had switched and bed-load material began to enter the Flemish Pass Basin from more proximal areas to the southeast with the Avalon zone basement. Overall, no evidence exists to support sediment sourcing from the Iberian margin or the Flemish Cap-Galicia Bank continental fragment to the east, and material from these areas is instead interpreted to have been shed into the incipient Atlantic Ocean or Bay of Biscay. Also, no evidence exists to support sourcing from Grenville basement farther to the west, implying that a drainage divide may have existed somewhere between central and western Newfoundland, west of which material was presumably being transported to the south or southwest.

Description: A method is proposed for identifying the carbon source for methane generated by carbonate-reduction microbial methanogenesis using the isotopic and compositional mass balance of carbon in cogenerated carbon dioxide (CO2) and methane. Microbial methanogenesis from bitumen or petroleum generates more methane than CO2, so the carbon isotopic compositions of methane and CO2 are relatively heavy and similar to the carbon isotopic composition of thermogenic methane. Microbial methanogenesis that uses kerogen or recent organic matter as a carbon source generates relatively more CO2 than methane; therefore, methane and CO2 have the light carbon typical of shallow microbial methane. This concept was quantified and tested against three literature examples to determine if the relative amount of CO2 generation could be estimated with sufficient resolution to predict source carbon type and generation temperature in gas shales and coalbed methane. Antrim Shale (Michigan) gases are demonstrated to be derived mainly from immature bitumen in the shale at modern reservoir temperatures and cooler temperatures. Fruitland coal gases in the western San Juan Basin are derived mainly from bitumen in oil-window maturity coals at modern temperature. Southwest Indiana coal gases are derived mainly from thermally immature kerogen at modern and warmer temperatures. Identification of the methane carbon source and temperature helps delineate microbial methane resource fairways, where fairways are limited by microbial gas generation. Temperatures may help determine if microbial methane is actively generated today or a relict from earlier microbial generation.

Description: The Guyana Basin is located along the passive margin of northeastern South America. With no major oil discoveries, the region is considered by the U.S. Geological Survey the second least explored basin in the world. We integrated approximately 3000 km ([~]1870 mi) of industry two-dimensional seismic data and 16 offshore wells in offshore Guyana to provide a regional framework and its hydrocarbon potential. Four main stratigraphic sequences from the Cretaceous to the Pliocene were recognized. Sequence 1 of the Cretaceous consists of shelfal sedimentation and submarine fan systems. The main Cretaceous depocenter is located in the southeastern part of the area, which coincides with a free-air gravity low, suggesting a basement depression inherited from Jurassic rifting. Sequence 2 of the Paleogene consists of shelfal clastic and carbonate deposits. Listric faults affect the shelf edge and slope, resulting in large turbidites down the slope. The west-southwest-east-northeast-oriented Waini arch developed along the northern shelf, and it may reflect a flexural long-distance effect of the Caribbean plate convergence with the northwestern South American plate. Sequence 3 of the early to middle Miocene consists of isolated carbonate platforms at the shelf edge surrounded by siliciclastics. On the sequence top, a regional unconformity was identified by large incised valleys. We suggest that this unconformity was caused by the peak of the Caribbean orogeny in the Trinidad area. Sequence 4 of the late Miocene to Pliocene shows the largest terrigenous progradational event in the shelf, which was built up by clear sigmoidal clinoforms. We suggest that the large progradation pattern change is caused by paleodrainage system changes in northern South America since the middle Miocene and by glacioeustasy.

Description: Isotopically reversed gases ({delta}13C methane 〉{delta} 13C ethane 〉 {delta}13C propane) occur in fractured mixed clastic-carbonate reservoirs of the Permian and the Triassic in the foothills at the western edge of the Western Canada sedimentary basin (WCSB). The{delta} 13C methane values (-42 to -24{per thousand}), gas dryness, and organic maturity (Ro 〉 2.2) are indicative of mature gases, and gas maturity generally increases with reservoir age and from the southeast to the northwest. The{delta} 13C ethane values range from -44 to -25, with the less negative values in isotopically normal gases to the northeast of the gas fields we studied. To explain the gas isotope reversals observed in the WCSB foothills, we adopt the concept of a closed-system shale, in which simultaneous cooking of kerogen, oil, and gas yields gas with light{delta} 13C ethane and heavy{delta} 13C methane. This gas was released from shales and trapped in fractured folds of brittle clastic-carbonate rocks during deformation and thrust faulting of the Laramide orogeny, creating some of the most prolific gas pools. These gases are actually mature shale gases. Local high abundances of H2S and CO2 are most likely the products of thermochemical sulfate reduction (TSR) reactions in anhydrite-rich interbeds and underbeds that admixed to the released shale gas during the tectonic event. No evidence exists that TSR is responsible for the isotope reversals. Variations in{delta} 13C ethane are likely caused by local differences in thermal history, the timing of gas release from shale, and the timing of the fault and fold development. Less negative {delta}13C ethane values (resulting in isotopically normal gases) to the northeast of the fields and in the underlying Devonian carbonates likely reflect a more open shale system where the earliest generated gas was lost. We suggest that isotopic reversals are restricted to closed-system maturation, and that their magnitude may be related to the relative volume of gas retained in shales.

Description: Deformation bands are commonly found in porous silicilastic sediments, where strain is accommodated by rotation, translation, and fracturing of individual grains instead of by the formation of a sharp discontinuity. We investigated deformation bands in a high-porosity carbonate rock from the Eisenstadt-Sopron Basin, on the border between Austria and Hungary, using a combination of microstructural and petrophysical methods. We used cathodoluminescence and electron microprobe analyses to assess the distribution and chemical composition of the carbonate particles, deformation bands, and cements. The earliest deformation bands formed before the cementation of the limestone, mainly by rotation of elongated bioclasts to an orientation parallel to the deformation bands. Further movement along the bands after the generation of blocky cement around the bioclasts resulted in cataclastic deformation of both allochems and cement. Moreover, we documented a reduction of porosity from 22 to 35% in the host rock to 2 to 5% in the deformation bands by microcomputed tomography and conventional helium porosimetry. Permeability is reduced as much as three orders of magnitude relative to the host rock, as documented by pressure decay probe permeametry. The observations indicate a change in physical properties of the rock caused by cementation during the generation of deformation bands, which results in a change of deformation mechanism from grain rotation and compaction to cataclastic deformation along a single band. The reduction of porosity and permeability, which is even stronger than observed in most silicilastic rocks, affects the migration of fluids in groundwater or hydrocarbon reservoirs.

Description: Forearc basins result from plate convergence. These basins are situated offshore between an outer-arc high and the mainland. Historically, these regions have not been considered important petroleum provinces partly because low heat flow may limit significant thermal hydrocarbon generation. The Simeulue forearc basin extends between Simeulue Island and northern Sumatra. It is a frontier shallow shelf area with few wells and no wells in the basin center; therefore, it is studied using geophysical data and geologic surface samples. Multichannel seismic data show bright spots above potential hydrocarbon reservoirs in carbonate buildups. Amplitude versus offset analyses indicate the presence of gas, and surface geochemical prospecting suggests thermal hydrocarbon generation. Heat flow in the Simeulue Basin ranges between 37 and 74 mW/m 2, as deduced from one-dimensional petroleum system modeling and bottom-simulating reflector depths. Two possible source rocks (Eocene and lower-middle Miocene) were assigned for three-dimensional petroleum system modeling in the Simeulue Basin. Because of a similar pre-Miocene geologic evolution of the present-day back arc and the fore arc, it can be assumed that the back-arc source rocks also occur in the fore arc. Modeling based on two heat-flow scenarios (40 and 60 mW/m 2) reveals that oil and gas generation is possible within and below the main depocenters of the central and southern Simeulue Basin. This study shows that deep burial (〉6 km [〉3.7 mi]) of source rocks can compensate for low heat flow. Therefore, forearc basins may be more prolific for hydrocarbons than previously considered, and each forearc basin should be studied carefully to evaluate its hydrocarbon potential.

Description: Three-dimensional seismic, wireline-log, core, and biostratigraphic data from the South Viking Graben, North Sea rift system, are integrated to investigate the controls on the temporal and spatial development of an Upper Jurassic synrift turbidite system deposited on the hanging-wall dipslope of a salt-influenced half graben. Turbidite deposition was coeval with the initiation and upslope (paleo-landward) migration of activity across a gravity-driven normal fault array. Three main synrift stratal units are identified, and these are mapped using seismic and well data. The lowermost unit (upper Oxfordian) comprises thick amalgamated turbidites, which are restricted to the hanging wall of the earliest, most basinward, growth fault. The middle unit (Kimmeridgian) is more areally extensive than the underlying system, draping the now inactive basinward growth fault and extending upslope into the hanging wall of a newly activated landward growth fault. The uppermost unit (lower to middle Volgian) is more sheetlike and was deposited when activity across all growth faults had mostly ceased and slope topography had been almost fully healed. This study demonstrates that hanging-wall dipslopes within rifts can be characterized by volumetrically significant, sand-rich, gravity flow-dominated depositional systems, and that the reservoir architecture of such deposits can be strongly controlled by syndepositional growth faulting. In addition, this study provides insights into the response of turbidites to tectonically driven changes in bathymetry, which may be applicable in a range of basin settings.

Description: We propose a flexible framework for evaluating prospect dependencies in oil and gas exploration and for solving decision-making problems in this context. The model uses a Bayesian network (BN) for encoding the dependencies in a geologic system at source, reservoir, and trap levels. We discuss different evaluation criteria that allow us to formulate specific decision problems and solve these within the BN framework. The BN model offers a realistic graphic model for capturing the underlying causal geologic process and allows fast statistical computations of marginal and conditional probabilities. We illustrate the use of our BN model by considering two situations. In the first situation, we wish to gain information about an area where hydrocarbons have been discovered, and use the value of perfect information to determine which locations are the best to drill. In the second situation, we consider the problem of abandoning an area when only dry wells are drilled. For this latter, we use an abandoned revenue criterion to determine the drilling locations. The application is from the North Sea. Our main focus is the description, visualization, and interpretation of the results for relating the statistical modeling to the local understanding of the geology.

Description: The Hidden Valley fault is exposed in Canyon Lake Gorge (central Texas) and cuts the Cretaceous Glen Rose Formation. This exposure provides an opportunity to explore the relationship between deformation mechanisms and fault displacement along 830 m (2723 ft) of a normal fault typical of those in carbonate reservoirs and aquifers around the world. The fault zone has five domains: gently deformed footwall damage zone, intensely deformed footwall damage zone, fault core, intensely deformed hanging-wall damage zone, and gently deformed hanging-wall damage zone. Footwall deformation is more intense and laterally extensive than hanging-wall deformation, and the intensely deformed hanging-wall damage zone is narrow and locally absent. The fault core contains thin clay-rich gouge or smear in most places but is locally represented by only a slickensided surface between limestone layers. The 55- to 63-m (180-207-ft) fault throw across a 43- to 98-m (141- to 322-ft)-wide fault zone is accommodated by slip along the fault core, layer tilting (synthetic dip development) in footwall and hanging-wall damage zones, and distributed faulting in footwall and hanging-wall damage zones. Total offset across the fault overestimates actual stratigraphic offset by 8 to 12 m (26-39 ft) or about 14 to 21%. In our interpretation, the Hidden Valley fault zone records both early extensional folding of the Glen Rose Formation and subsequent normal faulting that propagated downward from the overlying competent Edwards Group. The damage zone width is thus established before fault breakthrough.