Abstract Prudhoe Bay Field, the largest non-heavy-oil field in North America, has produced about 11 billion of 25 billion barrels of oil-in-place since production began in 1977. Co-owners ExxonMobil, ConocoPhilfield simulation modellips, and BP made the decision to build a new full-field model to evaluate future development decisions in the field. Requirements for the full-field, 12-component reservoir simulation model included a model size limit of about one million active cells and an areal grid block resolution of 5 acres (467ft/142m X 467ft/142m) and 10 to 15 feet (3.0m to 4.6m) vertically. The model incorporates approximately 2600 wells (about 1000 of which are horizontal), 1800 faults, all productive reservoir zones and other important geological controls on fluid flow such as shales and conglomeratic thief zones. A team composed of BP’s Alaskan geological, geophysical, petrophysical, and reservoir engineering staff; geocellular modelers from the three partner companies; and a consultant reservoir simulation engineer was assembled to build the model. The inclusion of operating company geoscience and engineering staff contributed specific expertise in the geology and reservoir engineering of Prudhoe Bay Field. The inclusion of multiple geocellular modeling staff contributed “best practices” from each partner company and also allowed key parts of the model, such as the structural framework and properties model, to be built concurrently, thus saving substantial time. The inclusion of the consultant reservoir simulation engineer having extensive experience with previous Prudhoe Bay full-field models provided continuity with prior modeling efforts.

Abstract The Kuparuk River Field, located on the North Slope of Alaska, is the second largest oil field in the U.S. Discovered in 1969 with production beginning in 1981, the reservoir interval extends over 280 square miles and has a gross thickness of 300 ft. STOOIP is estimated to be 6 BBO , of which 2 BBO have been produced to date. The field is produced from approximately 1000 wells on 160 acre spacing from 44 drill sites, employing a north-south line drive with waterflood, and miscible WAG processes. A major initiative has been undertaken to build a new full-field reservoir simulation model as a leveraging tool for managing the field performance. Key issues to be addressed using this model include EOR expansion to additional drill sites and field-wide evaluation of potential by-passed oil. In addition, this modeling work will support justification and planning of infill CTD (coil tubing drilling) and rotary wells. To support this reservoir engineering effort, a full-field geocellular model has been constructed, integrating 20 years of field data and reservoir characterization work. The full-field model consists of 151 million total cells of which approximately 20 million active cells are in the fine scale model. The fine scale model has been up-scaled in preparation for full field compositional flow simulation which, in turn, may impact flood design, EOR adjustments, data acquisition strategies, and budgetary long range planning. Small sectors of the model are extracted to look at individual well patterns in more detail. Using such sector models enables the identification, planning, and execution of infill drilling opportunities.

Abstract The Triassic-Jurassic Otuk Formation is a potentially important source rock in allochthonous structural positions in the northern foothills of the Brooks Range in the North Slope of Alaska. This study focuses on three localities of the Upper Triassic (Norian) limestone member, which form a present-day, 110-km-long, east-west transect in the central Brooks Range. All three sections are within the structurally lowest Endicott Mountain allochthon and are interpreted to have been deposited along a marine outer shelf with a ramp geometry. The uppermost limestone member of the Otuk was chosen for this study in order to better understand lateral and vertical variability within carbonate source rocks, to aid prediction of organic richness, and ultimately, to evaluate the potential for these units to act as continuous (or unconventional) reservoirs. At each locality, 1 to 4 m sections of the limestone member were measured and sampled in detail to capture fine-scale features. Hand sample and thin section descriptions reveal four major microfacies in the study area, and one diagenetically recrystallized microfacies. Microfacies 1 and 2 are interpreted to represent redeposition of material by downslope transport, whereas microfacies 3 and 4 have high total organic carbon (TOC) values and are classified as primary depositional organofacies. Microfacies 3 is interpreted to have been deposited under primarily high productivity conditions, with high concentrations of radiolarian tests. Microfacies 4 was deposited under the lowest relative-oxygen conditions, but abundant thin bivalve shells indicate that the sediment-water interface was probably not anoxic. The Otuk Formation is interpreted to have been deposited outboard of a southwest-facing ramp margin, with the location of the three limestone outcrops likely in relatively close proximity during deposition. All three sections have evidence of transported material, implying that the Triassic Alaskan Basin was not a low-energy, deep-water setting, but rather a dynamic system with intermittent, yet significant, downslope flow. Upwelling played an important role in the small-scale vertical variability in microfacies. The zone of upwelling and resultant oxygen-minimum zone may have migrated across the ramp during fourth- or fifth-order sea-level changes.

Abstract The Dunvegan Formation is a mid-Cretaceous alluvial plain-deltaic deposit exposed along the Rocky Mountain Foothills and Peace River Valley of Alberta and British Columbia, Canada. A multiproxy approach, combining paleosol micromorphology, geochemistry, and mineralogy with palynology, is used to reconstruct the climatic, pedogenic, and depositional history of this high-latitude setting during a greenhouse climate regime. Intrinsic features of paleosols within the Dunvegan Formation suggest a warm to cool temperate paleoclimate. These paleosols experienced multiple depositional phases superimposed on pedogenic phases that resulted in complicated compound, complex, and welded paleosol profiles. Well-preserved palynomorph assemblages within the paleosols are composed primarily of fern spores, with small percentages of gymnosperm pollen. The palynomorphs suggest a humid paleoclimate ranging from cool temperate to subtropical. The abundance of fern spores in all of the paleosol profiles suggests early successional colonization of the floodplain. Better-developed interfluve paleosols contain greater percentages of tree pollen, indicating the presence of nearby forests. Within interfluve paleosols, intervals barren of pollen coincide with sequence boundaries identified on the basis of micromorphology and geochemistry. Our combined paleopedological and palynological data sets, together with macrofloral and geochemical paleoclimate indicators, suggest that the Dunvegan alluvial-coastal plain complex probably formed under a humid, warm to cool temperate paleoclimate with a mean annual temperature (MAT) between 12 and 14° C and mean annual precipitation (MAP) between 1200 and 1300 mm yr -1 . These integrated data sets also provide a better understanding of the stratigraphic development of the coastal plains.

Abstract The Lisburne Group (Carboniferous-Permian) consists of a carbonate platform that extends for >1000 km across northern Alaska, and diverse margin, slope, and basin facies that contain world-class deposits of Zn and Ba, notable phosphorites, and petroleum source rocks. Lithologic, paleontologic, isotopic, geochemical, and seismic data gathered from outcrop and subsurface studies during the past 20 years allow us to delineate the distribution, composition, and age of the off-platform facies, and to better understand the physical and chemical conditions under which they formed. The southern edge of the Lisburne platform changed from a gently sloping, homoclinal ramp in the east to a tectonically complex, distally steepened margin in the west that was partly bisected by the extensional Kuna Basin (~200 by 600 km). Carbonate turbidites, black mudrocks, and radiolarian chert accumulated in this basin; turbidites were generated mainly during times of eustatic rise in the late Early and middle Late Mississippian. Interbedded black mudrocks (up to 20 wt% total organic carbon), granular and nodular phosphorite (up to 37 wt% P 2 O 5 ), and fine-grained limestone rich in radiolarians and sponge spicules formed along basin margins during the middle Late Mississippian in response to a nutrient-rich, upwelling regime. Detrital zircons from a turbidite sample in the western Kuna Basin have mainly Neoproterozoic through early Paleozoic U-Pb ages (~900-400 Ma), with subordinate populations of Mesoproterozoic and late Paleoproterozoic grains. This age distribution is similar to that found in slightly older rocks along the northern and western margins of the basin. It also resembles age distributions reported from Carboniferous and older strata elsewhere in northwestern Alaska and on Wrangel Island. Geochemical and isotopic data indicate that suboxic, denitrifying conditions prevailed in the Kuna Basin and along its margins. High V/Mo, Cr/Mo, and Re/Mo ratios (all marine fractions [MF]) and low MnO contents (<0.01 wt%) characterize Lisburne black mudrocks. Low Qmf/Vmf ratios (mostly 0.8-4.0) suggest moderately to strongly denitrifying conditions in suboxic bottom waters during siliciclastic and phosphorite sedimentation. Elevated to high Mo contents (31-135 ppm) in some samples are consistent with seasonal to intermittent sulfidic conditions in bottom waters, developed mainly along the basin margin. High d 15 N values (6-120) imply that the waters supplying nutrients to primary producers in the photic zone had a history of denitrification either in the water column or in underlying sediments. Demise of the Lisburne platform was diachronous and reflects tectonic, eustatic, and environmental drivers. Southwestern, south-central, and northwestern parts of the platform drowned during the Late Mississippian, coincident with Zn and Ba metallogenesis within the Kuna Basin and phosphogenesis along basin margins. This drowning was temporary (except in the southwest) and likely due to eutrophication associated with upwelling and sea-level rise enhanced by regional extension, which allowed suboxic, denitrifying waters to form on platform margins. Final drowning in the southcentral area occurred in the Early Pennsylvanian and also may have been linked to regional extension. In the northwest, platform sedimentation persisted into the Permian; its demise there appears to have been due to increased siliciclastic input. Climatic cooling may have produced additional stress on parts of the Lisburne platform biota during Pennsylvanian and Permian times.

Abstract A primary mechanism likely to control potential gas production from gas-hydrate-bearing porous media is the gas-water two-phase flow during dissociation. Gas-water relative-permeability functions within gas-hydrate systems are poorly understood, and direct measurements within gas-hydrate-bearing porous media are difficult. In this study, we developed a new method for measuring gas-water relative permeability for laboratory-synthesized gas hydrate within porous media. The new experimental design allows gas hydrate to form within a porous media and allows the measurement of effective permeability and relative permeability for different saturation values. The relative permeability to gas and water was determined by applying the Johnson-Bossler-Neumann method. Finally, effective permeability and relative permeability data of gas and water phases are reported for gas-hydrate-saturated consolidated Oklahoma 100-mesh sand and Alaska North Slope subsurface sediments. The results show significant reduction in permeability at increased gas-hydrate saturations. The results also suggest that the relative permeability determined from the unsteady-state core floods is primarily affected by gas-hydrate saturations. Furthermore, effective as well as relative permeabilities vary by the nature of gas-hydrate distribution for the same bulk saturation in different porous media. We believe that the experimental data obtained from this work will provide input data to reservoir modeling, fluid flow modeling, and development of relative-permeability-estimation methods for hydrate production. However, considerable additional experimental and theoretical work remains to develop an analytical or generalized model to predict the relative permeability for gas-hydrate reservoir simulation.