ALBERT

Description: A 300-m (1000-ft)-thick succession of shallow- and warm-water carbonates has been studied in well cores from the southernmost Barents Sea, offshore north Norway. These upper Paleozoic strata contain numerous zones of moderate to high porosity, including a wide range of depositional facies, despite moderately high burial temperatures and the absence of petroleum charge. Most porosity appears to be either primary or created during early (eogenetic) diagenesis. Negative correlation between porosity and both bulk-rock alumina content and stylolite frequency reflects the influence of phyllosilicate minerals in localizing stylolitic dissolution. This provides part of the explanation for the overall correlation between porosity and the platform's stratigraphic evolution. The early stage of mixed siliciclastic-carbonate deposition has low porosity because of extensive chemical compaction in aluminous beds. The following siliciclastic-poor stage shows upward-increasing porosity associated with aggradation of muddy buildups and wackestones, followed by the progradation of a more proximal facies belt of thinly bedded dolomitic mudstones. Maximum porosity development occurs in the overlying, little-dolomitized grain-shoal facies belt, which shows upward decrease in porosity because of a transgressive trend that developed progressively lower energy depositional conditions, favoring the occurrence of stylolite-prone shaly laminations. A general porosity-favorable factor is the presence of a stratified column of high-salinity brine, enforcing a closed diagenetic system during burial. Limestones and dolostones comprising this platform have very different proportions of low and high porosity values. Limestones have positively skewed frequency distribution (many samples 〈5% porosity), whereas dolostones have higher average porosity with symmetric distribution (few samples 〈5% porosity). The low limestone porosities result from cementation by coarse calcite-spar in grain-dominated samples and matrix compaction and cementation in muddy facies, features that are less common in dolostones possibly because of lesser propensity for stylolite development and the resistance of early-dolomitized matrix to compaction. Steve received a Ph.D. from the University of California at Los Angeles in 1978. He works on sandstone and carbonate petrology, sedimentology, and stratigraphy.

Description: Reservoir characterization, modeling, and simulation were undertaken to improve production from Womack Hill field (eastern Gulf Coast, United States). This field produces oil from Upper Jurassic Smackover carbonate shoal reservoirs. These reservoirs occur in vertically stacked, heterogeneous depositional and porosity cycles. The cycles consist of lime mudstone and wackestone at the base and ooid grainstone at the top. Porosity has been enhanced through dissolution and dolomitization. Porosity is chiefly interparticle, solution-enlarged interparticle, grain moldic, intercrystalline dolomite, and vuggy pores. Dolostone pore systems and flow units have the highest reservoir potential. Petroleum-trapping mechanisms include a fault trap (footwall uplift with closure to the south against a major west-southeast–trending normal fault) in the western area, a footwall uplift trap associated with a possible southwest-northeast–trending normal fault in the south-central area, and a salt-cored anticline with four-way dip closure in the eastern area. Potential barriers to flow are present as a result of petrophysical differences among and within the cycles, as well as the presence of normal faulting. Reservoir performance analysis and simulation indicate that the unitized western area has less than 1 MMSTB of oil remaining to be recovered, and that the eastern area has 2–3 MMSTB of oil to be recovered. A field-scale reservoir management strategy that includes the drilling of infill wells in the eastern area of the field and perforating existing wells in stratigraphically higher porosity zones in the unitized western area is recommended for sustaining production from the Womack Hill field. Ernest A. Mancini is regional director of the Eastern Gulf Region of the Petroleum Technology Council, director of the Center for Sedimentary Basin Studies, and professor in petroleum geology in the Department of Geological Sciences at the University of Alabama. His research focus is on reservoir characterization and modeling, petroleum systems, and the application of stratigraphic analysis to petroleum exploration.Tom Blasingame is an associate professor in the Department of Petroleum Engineering at Texas A&M University. He holds B.S. and M.S. degrees and a Ph.D. from Texas A&M University in petroleum engineering. He is a distinguished member of the Society of Petroleum Engineers and a member of the Society for Exploration Geophysicists and AAPG. Rosalind Archer holds a Ph.D. in petroleum engineering from Stanford University. Her research interests are in reservoir characterization, well testing, and reservoir simulation. She is currently a lecturer in the Department of Engineering Science at the University of Auckland, Auckland, New Zealand. She is also an adjunct assistant professor in the Department of Petroleum Engineering at Texas A&M University. Brian Panetta is a research associate in the Department of Geological Sciences at the University of Alabama. He received a B.S. degree from the University of South Carolina, an M.S. degree from the University of Kentucky, and an M.S. degree and a Ph.D. from the University of Alabama. His research interests are in reservoir characterization and geologic modeling. Juan Carlos Llinás obtained his B.A degree from the National University of Colombia in 1995 and his M.S. degree in 2003 from the University of Alabama, and he is currently working on his Ph.D. at the University of Alabama. He works in geologic modeling of oil fields with siliciclastic and carbonate reservoirs using well-log, core, and seismic data. Charles D. Haynes is a businessman and educator with degrees in mining and petroleum engineering. He was an independent petroleum producer before joining the faculty at the University of Alabama. He continues his professional practice through minerals-related research, consulting, and joint ownership of an independent oil-producing company. He serves on the State Board of Licensure for Engineers and Land Surveyors. Joe Benson is a professor in the Department of Geological Sciences and senior associate dean of the College of Arts and Sciences at the University of Alabama. His research interests lie in carbonate sedimentology and sedimentary petrology. He received a B.A. degree from the College of Wooster and an M.S. degree and a Ph.D. from the University of Cincinnati.

Description: The 87Sr/86Sr compositions of formation waters that were collected from 71 wells producing from a Pennsylvanian carbonate reservoir in New Mexico display a well-defined distribution, with radiogenic waters (up to 0.710129) at the updip western part of the reservoir, grading downdip to less radiogenic waters (as low as 0.708903) to the east. Salinity (2800–50,000 mg/L) displays a parallel trend; saline waters to the west pass downdip to brackish waters. Elemental and isotopic data indicate that the waters originated as meteoric precipitation and acquired their salinity and radiogenic 87Sr through dissolution of Upper Permian evaporites. These meteoric-derived waters descended, perhaps along deeply penetrating faults, driven by gravity and density, to depths of more than 7000 ft (2100 m). The 87Sr/86Sr and salinity trends record influx of these waters along the western field margin and downdip flow across the field, consistent with the strong water drive, potentiometric gradient, and tilted gas-oil-water contacts. The formation water 87Sr/86Sr composition can be useful to evaluate subsurface flow and reservoir behavior, especially in immature fields with scarce pressure and production data. In mature reservoirs, Sr isotopes can be used to differentiate original formation water from injected water for waterflood surveillance. Strontium isotopes thus provide a valuable tool for both static and dynamic reservoir characterization in conjunction with conventional studies using seismic, log, core, engineering, and production data. Roger Barnaby has conducted stratigraphic studies of carbonates and siliciclastics in outcrop and subsurface for 15 years. He holds a Ph.D. from Virginia Polytechnic Institute and a B.S. degree from East Carolina University. Barnaby has worked on sedimentary successions of the Gulf Coast, Permian basin, Alaska North Slope, Middle East, and Caspian region. He maintains interests in carbonate diagenesis and geochemistry.Gregg Oetting received an M.A. degree in geology in 1995 from the University of Texas at Austin. He is the author of six publications concerning geochemical and strontium isotopic variations in Edwards aquifer groundwaters. For the past seven years, Oetting has traded energy futures for leading merchant energy concerns. He works for an independent consulting business in Houston, Texas. Guoqiu Gao received his B.S and M.S. degrees in geology from Central-South University, Hunan, China, and his Ph.D. in geology from the University of Texas at Austin. He works for a major oil company in Houston, Texas. His current interests lie in the field of geoscience computing.

Description: In the northeastern Gulf of Mexico, Upper Jurassic Smackover inner ramp, shallow-water thrombolite buildups developed on paleotopographic features in the eastern part of the Mississippi Interior Salt basin and in the Manila and Conecuh subbasins. These thrombolites attained a thickness of 58 m (190 ft) and were present in an area of as much as 6.2 km2 (2.4 mi2). Although these buildups have been exploration targets for some 30 yr, new field discoveries continue to be made in this region. Thrombolites were best developed on a hard substrate during a rise in sea level under initial zero to low background sedimentation rates in low-energy and eurytopic paleoenvironments. Extensive microbial growth occurred in response to available accommodation space. The demise of the thrombolites corresponded to changes in the paleoenvironmental conditions associated with an overall regression of the sea. The keys to drilling successful wildcat wells in the thrombolite reservoir play are to (1) use three-dimensional seismic reflection technology to find paleohighs and to determine whether potential thrombolite reservoir facies occur on the crest and/or flanks of these features and are above the oil-water contact; (2) use the characteristics of thrombolite bioherms and reefs as observed in outcrop to develop a three-dimensional geologic model to reconstruct the growth of thrombolite buildups on paleohighs for improved targeting of the preferred dendroidal and chaotic thrombolite reservoir facies; and (3) use the evaporative pumping mechanism instead of the seepage reflux or mixing zone models as a means for assessing potential dolomitization of the thrombolite boundstone. Ernest A. Mancini is regional director of the Eastern Gulf Region of the Petroleum Technology Council, director of the Center for Sedimentary Basin Studies, and professor in petroleum geology in the Department of Geological Sciences at the University of Alabama. His research focus is on reservoir charactertization and modeling, petroleum systems, and the application of stratigraphic analysis to petroleum exploration.Juan Carlos Llinás obtained his B.A degree from the National University of Colombia in 1995 and his M.S. degree in 2003 from the University of Alabama, and he is currently working on his Ph.D. at the University of Alabama. He is studying Smackover oil fields associated with microbial reef buildups and genetically related depositional facies using well and seismic data. William Parcell is an assistant professor in the Department of Geology at Wichita State University. His research integrates sequence stratigraphy, microbial sedimentology, and soft-computing techniques in stratigraphic modeling. He received his B.S. degree (1994) from the University of the South (Sewanee, Tennessee), his M.S. degree (1997) from the University of Delaware, and his Ph.D. from the University of Alabama (2000). Marc Aurell received his B.A. degree (1985) and his Ph.D. (1990) in geology from Zaragoza University. He is currently working at Zaragoza University as a professor. Most of his work in the last 20 years has been concentrated on facies and sequence-stratigraphic analysis of the Mesozoic and Cenozoic carbonate platforms developed in the Iberian basin and in the Pyrenees (Spain). Beatriz Bádenas obtained her B.A. degree (1991) and her Ph.D. (1999) in geology at Zaragoza University, where she teaches courses in stratigraphy and sedimentology. Her major research interests include facies and sequential analysis of carbonate sediments in shallow platform settings. She is currently studying the application of high-resolution sequence stratigraphy and cyclostratigraphy to Upper Jurassic carbonate platform strata of the Iberian basin. Reinhold Leinfelder, paleontologist, carbonate sedimentologist, and basin analyst, specializes in Jurassic reef systems. He received his Diploma degree from the University of Munich in 1980 and his Ph.D. in 1985 and a postdoctoral habil degree in 1989 from the University of Mainz. He was an associate professor at the University of Stuttgart (1989–1998), and he is now a full professor at the University of Munich. Joe Benson is a professor in the Department of Geological Sciences and senior associate dean of the College of Arts and Sciences at the University of Alabama. His research interests lie in carbonate sedimentology and sedimentary petrology. He received a B.A. degree from the College of Wooster and an M.S. degree and a Ph.D. from the University of Cincinnati.

Description: The high-pressure and high-temperature (HPHT) areas of the central North Sea constitute an important hydrocarbon province. This includes the deep, Mesozoic reservoirs in United Kingdom quadrants 22, 23, 29, and 30. This study was undertaken to better understand oil and gas compositional histories in HPHT hydrocarbon systems and to help identify new exploration opportunities. The Late Jurassic Kimmeridge Clay Formation has been the source for both oil and gas over the entire area, with additional gas charge from the humic coals of the Middle Jurassic Pentland Formation in the western graben areas. The southern Forties Montrose high, with its southward-plunging Mesozoic terraces, is host to numerous oil and gas fields with temperatures ranging from 90 to 180°C and formation pressures whose gradient to the surface exceeds 0.8 psi/ft (0.192 MPa/m). Several of these oil accumulations have undergone in-reservoir thermal cracking, resulting in a lighter, single-phase fluid, together with a pyrobitumen residue in the pore volumes. With several traps at or near their leak-off pressure, the likelihood of top seal failure and gas leakage is prevalent. Such top seal failure is intermittent and, in some instances, is associated with gas chimneys. The main causes of pressure increase in Mesozoic sediments are thought to be volume increases associated with gas generation from source rocks, clay dehydration, and thermal cracking of oil. Top seal failure because of pressure buildup by salt diapirism and the buoyancy of large hydrocarbon columns has resulted in a series of compositionally fractionated oils and gases. A new technique is presented, whereby the geochemical character of a shallow (Tertiary) oil reservoir that has undergone fractionation can help lower the risk of detecting the presence of hydrocarbon at depth in potential, deep (Mesozoic) reservoirs. Gary Isaksen coordinates geoscientists and technical programs in ExxonMobil's Upstream Geoscience companies. Isaksen holds B.Sc. and M.Sc. degrees and a Ph.D. from the University of Bergen, Norway. Since he joined Exxon in 1985, he has worked on hydrocarbon system analyses in numerous sedimentary basins worlwide as well as the application of petroleum geochemistry to development and production.