ALBERT

Description: The Triassic successions of the Colorado Plateau preserve an important record of vertebrate evolution and climate change, but correlations to a global Triassic framework are hampered by a lack of geochronological control. Tuffaceous sandstones and siltstones were collected from the Upper Triassic Chinle Formation exposed in the Petrified Forest National Park, Arizona, USA, within a refined stratigraphic context of 31 detailed measured sections. U-Pb analyses by the isotope dilution-thermal ionization mass spectrometry (ID-TIMS) method constrain maximum depositional ages for nine tuffaceous beds and provide new insights into the depositional history of the Chinle fluvial system. The base of the Blue Mesa Member of the Chinle Formation is placed at ca. 225 Ma, and the top of the Petrified Forest Member is placed at 208 Ma or younger, bracketing an [~]280-m-thick section that spans nearly the entire Norian Stage of the Late Triassic. Estimated sediment accumulation rates throughout the section reflect extensive hiatuses and/or sediment removal by channel erosion. The new geochronology for the Chinle Formation underscores the potential pitfalls of correlation of fluvial units based solely on lithostratigraphic criteria. A mid-Norian age (ca. 219-213 Ma) for the distinctive Sonsela conglomeratic sandstone bed constrains the Adamanian-Revueltian land vertebrate faunachron boundary. Our new data permit a significant time overlap between the lower Chinle sequence and the dinosauromorph-rich Ischigualasto Formation of northwestern Argentina. Near-contemporaneity of the trans-American deposits and their faunal similarities imply that early dinosaur evolution occurred rapidly across the Americas.

Description: Paleosol properties are routinely characterized by whole-rock geochemistry, compromising the interpretation of important biogeochemical information in deep time. As a consequence, we employ a new pedotransfer function approach to the characterization of paleosols and apply this methodology to Late Cretaceous (Campanian and Maastrichtian) and early Paleocene (Danian) landscapes from the Dawson Creek study area of the western interior to: (1) reconstruct collodially based physical and chemical soil properties, and (2) assess climate and soil biogeochemical controls on evolving terrestrial ecosystems. Nine paleoseries (i.e., pedotypes) characterize the range of soil properties within the fluvial stratigraphic succession, which includes Entisols, Inceptisols, and Vertisols. All soils had optimal water-holding potential as inferred from low bulk densities, whereas poorly drained and colonizing landscapes likely suffered from poor aeration during seasonal water logging. Even with high water-holding capacity, Maastrichtian soils experienced seasonal moisture stress because of lower rainfall than Campanian and Danian soils. Fertility levels were sufficient for the growth of most plants judging from high cation exchange capacity and base saturation, negligible aluminum toxicities because of nonacid pH, and limited salinity and sodicity from relatively low exchangeable sodium and soluble salts in solution. Unlike warm-temperate and forested paleosols with neutral pH from the Campanian and Danian, subtropical and alkaline paleosols from the Maastrichtian apparently supported a woodland plant formation adapted to low availability of iron and manganese, which were fixed with calcium in carbonate, and low availability of phosphorous because it formed insoluble compounds with iron and manganese. Carbon, nitrogen, phosphorous, and sulfur cycling through microbially mediated mineralization of soil organic matter was limited from low litter inputs in both early and midsuccessional ecosystems, particularly in woodland soils. Results do not reveal demonstrable changes in soil characteristics through the K-T transition.

Description: The Upper Triassic Sonsela member of the Chinle Formation in the Petrified Forest National Park was evaluated using sedimentologic, stratigraphic, paleopedologic, and petrographic criteria along a continuous 0.5-km (0.3-mi) outcrop. The study interval consists of interbedded sandstones and mudstones and is composed of a two-tiered hierarchy of cyclic alluvial deposits with bounding paleosols. The succession is composed of 15 fluvial aggradational cycles (FACs) that comprise two FAC sets (FAC-Sets). The FAC-Sets are composed of architectural elements suggestive of a mixed-load fluvial system that is alternately dominated by bed-load deposits and suspended-load deposits. A thinning and fining stacking pattern within FAC-Sets is accompanied by an upward increase in pedogenic modification, suggesting that cycles systematically stack in response to a longer period decrease in the rate of accommodation gain. Sandstones are classified as litharenites, feldspathic litharenites, and lithic subarkoses, and occur within recycled orogen, dissected arc, and transitional arc provenance fields. Sandstone compositional maturity increases upward through the FAC-Sets. Point counts of intergranular volume (as a proxy for primary porosity) within channel facies and subsequent transform to syndepositional permeability provide a two-dimensional depiction of the lateral variability in reservoir quality. Paleosols are weakly to moderately developed and have little stratigraphic variation. These characteristics suggest that climatic fluctuations are not responsible for evolving fluvial depositional style or associated reservoir quality. Trends in sandstone compositional maturity suggest that fluvial stacking patterns and depositional style are related to pulses of tectonism. Sandstones are volcanogenic rich and have undergone an almost complete diagenetic loss of porosity caused by the precipitation of authigenic clays. Paragenetic reconstruction suggests that porosity loss occurred contemporaneous with the silicification of fossil logs in channel deposits. Log compaction at the time of silicification averaged 9.1%, suggesting that log silicification and porosity loss occurred soon after deposition.

Description: Oil has been continuously produced from the Devonian Leduc Formation at Innisfail field since its discovery in 1957. To date, cumulative production at Innisfail is 98.9% of recoverable oil in place (84.3 MMBO) and indicates that the Leduc is near the end of its productive life. A sequence-stratigraphic interpretation produced from core, well logs, and three-dimensional (3-D) reflection seismic data, however, suggests that production may be extended through the development of two previously undetected scenarios of bypassed oil entrapment: (1) attic oil accumulations associated with small buildups atop the isolated Innisfail platform and (2) backstep-edge accumulations located in positions structurally low to currently producing wells. In both cases, oil accumulations are related to a Leduc depositional history that was characterized by rates of long-term carbonate sediment accumulation exceeded by the rate of sea level rise. Positive bathymetric relief created at the time of deposition and, subsequently, present-day stratigraphic traps were produced during the final phase of stratal retrogradation that immediately preceded the drowning of the isolated Innisfail platform. High-quality 3-D seismic data are essential in the exploration for both attic and backstep-edge oil accumulations at Innisfail. Integration of 3-D seismic data, well-log, and core data indicates that although depositional relief on both types of features may be low, they are nonetheless seismically resolvable. The small platform-top buildups are up to 0.16 km2 (40 ac) in diameter and have up to 10 m (33 ft) of independent closure above spill point. Backstep-edge oil accumulations occur within the structurally highest parts of the Leduc high-frequency sequence G downlap limit. Depositional relief along the downlap limit and associated trap closure ranges from approximately 5 to 15 m (16 to 49 ft). During 2003 and 2004, two platform-top buildups were directionally drilled, and one existing well located near a backstep-edge position and suspended since 1988 was reactivated. All three wells are successful and, to date, have cumulative production of 71 thousand bbl of oil. A total of 17 platform-top buildups and backstep-edge development drilling prospects exist across Innisfail and have expected-case recoverable reserves of approximately 960 thousand bbl of oil. These reserve additions suggest the potential for 1.14% field growth at Innisfail and are representative of the potential value that may yet exist within all mature Leduc fields in western Canada. Stacy Atchley received his B.S. and M.S. degrees from Baylor University in 1984 and 1986 and his Ph.D. from the University of Nebraska in 1990. After working for Exxon Company, U.S.A., and Exxon Production Research from 1986 to 1995, Stacy rejoined Baylor, where he currently directs the Applied Petroleum Studies Program and is a researcher in the Ancient Environment Reconstructions Research Group. Lawrence West received his B.Sc. (hons.) degree in geology from McMaster University in 1979 and his M.B.A. from the University of Calgary in 1989. His career began with Esso Resources Canada, Ltd., and Alberta Energy Company. He is currently the vice president of Geoscience with Auriga Energy Inc. Revitalization of mature fields is an area of interest. Jeff Sluggett received his B.A.Sc. degree in geological engineering from the University of British Columbia in 1973. Jeff worked as an explorationist for Amoco Canada from 1973 to 1980 and was chief geophysicist and international corporate exploration advisor for Ranger Oil from 1980 to 2000. Jeff currently works for several companies in Calgary as a geophysical consultant specializing in three-dimensional seismic interpretation.

Description: The organic facies concept states that kerogen abundance and composition are relatable to depositional settings. This link has been extended, using open-system pyrolysis methods, to include major petroleum types whose gross compositions are inherently defined by source rock kerogens and, hence, to petroleum composition, which directly controls the physical response of fluids to changing pressure and temperature conditions during secondary migration. The possibility to model petroleum composition during hydrocarbon generation as well as the phase behavior of the fluids during migration is now available in modern basin modeling software. However, whereas pyrolysis methods can accurately reconstruct hydrocarbon gas:oil ratios and liquid compositions, they are inherently incapable of correctly reproducing the gas composition of natural fluids, and because the gas composition dominantly controls the phase behavior of petroleums, multicompound compositional kinetic predictions based on pyrolysis results alone are inappropriate for the prediction of phase behavior. The new PhaseKinetics approach described here combines open- and closed-system pyrolysis techniques to characterize the compositional evolution of the fluids generated as a function of increasing thermal stress, as well as correcting experimentally determined gas compositions and, therefore, overcomes these deficiencies. It has been used to develop compositional kinetic schemes capable of predicting natural petroleum phase behavior for different organofacies types. The methodology uses a compositional description of the generated fluids similar to that used in pressure-volume-temperature (PVT) simulation. Selected studies in the Norwegian North Sea, Brazil, and Mexico demonstrate the quality of the tuned compositional predictions for different organic facies types. Rolando di Primio joined the GeoForschungsZentrum Potsdam as a senior research scientist in 2001 after having worked as an exploration geologist in the Norwegian petroleum industry for several years. He holds a diploma in geology from the RWTH (Rheinisch-Westphälische Technische Hochschule) Aachen, Germany, and a Ph.D. from the University of Cologne. His research interests are hydrocarbon phase behavior, basin modeling, and organic geochemistry. Brian Horsfield is a professor of organic geochemistry and hydrocarbon systems at the Technical University of Berlin, Germany, and leads the Organic Geochemistry Section at GeoForschungsZentrum Potsdam. He has 27 years of experience working with and for industry in upstream research and development. His research interests include predicting fluid compositions ahead of drilling in petroleum systems and unraveling the workings of the deep biosphere.

Description: Oil resources at Valhalla field of west-central Alberta, Canada, are stratigraphically trapped within the Upper Cretaceous Doe Creek Member of the Kaskapau Formation. The reservoir is subdivided into four thin (1–10 m [3–33 ft]), cyclic alternations of offshore mudrock and shoreface sandstone that are designated the I − 1, I, I + 1, and I + 2 units. The thickest and most widespread I sandstone is the primary reservoir. Optimum reservoir quality corresponds to coarser grain shoreface sandstone; however, reservoir quality may be diminished by postdepositional calcite cement commonly observed near the top of shoreface sandstones. Open-hole well logs are used to predict depositional facies and calcite cement occurrence in wells that lack core control. Decreasing shale volume ( V sh) and increasing deep resistivity values correspond to progressively shallower water deposits. Zones of calcite-cemented shoreface sandstone greater than 0.5 m (1.6 ft) thick are interpreted when the neutron porosity exceeds the density porosity by more than 7%. Facies distributions predicted for the I sandstone closely match trends of the sandstone gross pore volume and daily total fluid production, and suggest that open-hole well logs may be used to anticipate reservoir quality and continuity. Regional and local observations support previous interpretations that attribute the Doe Creek to forebulge erosion and southwestward sediment transport toward a foredeep where shoreface sandstones accumulated within a coastal embayment to the Western Interior seaway. Regionally, the Doe Creek interval thins northeast of Valhalla and is truncated beneath the K1 unconformity, and shoreface sandstone bodies are encased within offshore mudrocks and detached from their contemporaneous shoreline. Locally at Valhalla, the Doe Creek reservoir progrades toward the southwest and is extensively and commonly uniformly burrowed by a relatively diverse assemblage of trace makers. Stacy Atchley received his B.S. and M.S. degrees from Baylor University in 1984 and 1986, and Ph.D. from the University of Nebraska, Lincoln, in 1990. After working for ExxonMobil from 1986 to 1995, he rejoined Baylor where he directs the applied petroleum studies program and is a researcher within the paleoclimate research group. Nathaniel Ball received both his B.S. (2006) and M.S. (2009) degrees in geology from Baylor University. He recently began his career as a geologist with Nexen Petroleum U.S.A. Inc. and is currently working in the Gulf of Mexico. Luke Hunt received his honors B.S. degree in geosciences from McMaster University in 2007 and his M.S. degree from Baylor University in 2009. He currently works for Husky Energy as a member of the geological services exploration team.