Umiat Oil Research Articles

Machine Learning-Based Probabilistic Lithofacies Prediction from Conventional Well Logs: A Case from the Umiat Oil Field of Alaska

A good understanding of different rock types and their distribution is critical to locate oil and gas accumulations in the subsurface. Traditionally, rock core samples are used to directly determine the exact rock facies and what geological environments might be present. Core samples are often expensive to recover and, therefore, not always available for each well. Wireline logs provide a cheaper alternative to core samples, but they do not distinguish between various rock facies alone. This problem can be overcome by integrating limited core data with largely available wireline log data with machine learning. Here, we presented an application of machine learning in rock facies predictions based on limited core data from the Umiat Oil Field of Alaska. First, we identified five sandstone reservoir facies within the Lower Grandstand Member using core samples and mineralogical data available for the Umiat 18 well. Next, we applied machine learning algorithms (ascendant hierarchical clustering, self-organizing maps, artificial neural network, and multi-resolution graph-based clustering) to available wireline log data to build our models trained with core-driven information. We found that self-organizing maps provided the best result among other techniques for facies predictions. We used the best self-organizing maps scheme for predicting similar reservoir facies in nearby uncored wells—Umiat 23H and SeaBee-1. We validated our facies prediction results for these wells with observed seismic data.

Integrated reservoir characterization and simulation of a shallow, light-oil, low-temperature reservoir: Umiat field, National Petroleum Reserve, Alaska

Umiat field in northern Alaska is a shallow, light-oil accumulation with an estimated original oil in place of more than 1.5 billion bbl and 99 bcf associated gas. The field, discovered in 1946, was never considered viable because it is shallow, in permafrost, and far from any infrastructure. Modern drilling and production techniques now make Umiat a more attractive target if the behavior of a rock, ice, and light oil system at low pressure can be understood and simulated. The Umiat reservoir consists of shoreface and deltaic sandstones of the Cretaceous Nanushuk Formation deformed by a thrust-related anticline. Depositional environment imparts a strong vertical and horizontal permeability anisotropy to the reservoir that may be further complicated by diagenesis and open natural fractures. Experimental and theoretical studies indicate that there is a significant reduction in the relative permeability of oil in the presence of ice, with a maximum reduction when connate water is fresh and less reduction when water is saline. A representative Umiat oil sample was reconstituted by comparing the composition of a severely weathered Umiat fluid to a theoretical Umiat fluid composition derived using the Pedersen method. This sample was then used to determine fluid properties at reservoir conditions such as bubble point pressure, viscosity, and density. These geologic and engineering data were integrated into a simulation model that indicate recoveries of 12%–15% can be achieved over a 50-yr production period using cold gas injection from five well pads with a wagon-wheel configuration of multilateral wells.

Integrated geologic modeling and reservoir simulation of Umiat: A frozen shallow oil accumulation in national petroleum reserve of Alaska

Current high oil price and availability of new technologies allow re-evaluation of oil resources previously considered uneconomic. The Umiat oil field is one such resource: a unique, shallow (275−1055ft), low-pressure (200−400psia) reservoir within the permafrost zone with no initial gas cap, located north of the Arctic Circle, 80miles west of the Trans Alaska Pipeline System (TAPS) with an estimated 1.5 billion barrels of oil in place.A static model was built based on reinterpretation of original log and core data and seismic information. A permeability anisotropy ratio of 0.45 was incorporated into the geologic model. A Monte Carlo simulation was conducted to estimate the different degrees of uncertainty in the original oil in place (OOIP) estimates. To cover the wide permeability range (0–500md), three sand groups (rock types) were defined and assigned appropriate capillary pressure and relative permeability curves. These were included in the dynamic model along with measured PVT data and gas–oil relative permeabilities in the presence of ice to evaluate the performance of immiscible gas injection using a multilateral wagon wheel well pattern with horizontal well length of 1500ft.The new simulation results show that with 50years of gas injection, recovery factors for the base case (400psia injection pressure) and two cases with 600 and 800psis injection pressures are 10.81%, 13.77%, and 16.66% respectively, keeping other parameters constant. These recovery numbers will reduce by 14% and 9% when producing GOR is restricted to 5000scf/STB and 10,000scf/STB, respectively. Due to unknown characteristics of natural fractures, several permeability anisotropy (Kv/Kh) ratios were considered. Simulation results indicate that lower anisotropy ratio will reduce oil recovery, probably due to inhibition in the downward movement of gas.The result obtained by this study contributes to the understanding of uncertainties in resource estimates and evaluating ranges of oil recovery in reservoir modeling. Despite limited data and lack of production history to tune the model, the results demonstrate that the economics of the proposed development plan bear a high degree of uncertainty and risk. These findings strongly encourage the operator to include development plan strategies to reduce the risk and enhance the quantity and quality of input simulation data.

Central Arctic Foothills, Alaska: A Unique Challenge in Frontier Exploration: ABSTRACT

Chevron U.S.A. has under lease nearly 2 million acres (800,000 ha.) of Arctic Slope Regional Corporation lands in the foothills of the Brooks Range between the Chukchi Sea and Canning River. In the central foothills, between the National Petroleum Reserve-Alaska and the Alaska pipeline, Chevron has conducted extensive field programs and air photo mapping, recorded 3,000 km (1,865 mi) of seismic data, and drilled three exploratory wells. The Brooks Range foothills are underlain by complex thrust plates and associated foreland folds which contain deformed rocks ranging in age from Devonian to middle Cretaceous. Main thrusting occurred in latest Jurassic to Albian time, corresponding to an arc-continent collision possibly associated with the widening of the Canada basin. First orogenic pulses are recorded by Upper Jurassic turbidites and olistostrome units which reveal a southern clastic source, a major reversal in source direction from older sedimentary units. Lower Cretaceous foreland turbidites show progressive northward migration of underthrusted imbricating plates. In the thrust belt, the primary reservoir objective is Lisburne limestone and dolomite, Mississippian to Permian in age. Seismic data identify a variety of structural styles of Lisburne plates ranging from complex stacks of imbricates to a single leading-edge plate underthrust by Lower Cretaceous foreland clastic units. Pore space in dolomitic Lisburne is filled with solid bitumen nearly everywhere on the surface in the central foothills, suggesting that extensive amounts of oil have migrated through End_Page 495------------------------------ the rocks, and in at least one area, accumulated in older traps. Rich, oil-prone source beds and oil shales occur in rocks ranging from Devonian to Early Cretaceous in age. These rocks are typically mature or post-mature on surface thrust plates in the heart of the thrust belt, but become significantly less mature to the north along the leading edge thrusts. In the fold belt, the primary objective is Lower Cretaceous sandstone. Surface and seismic mapping reveal numerous open folds, whose location is controlled by more deeply seated thrust fault geometry. Cretaceous shale units are typically gas-prone and organic-lean, but the Umiat field demonstrates that oil has migrated into shallow structures, perhaps from a significant distance. Also, residual oil shows are common in many wells throughout the fold belt. The relationship of the source of the Umiat oil to the fold and thrust belt and its implications for exploration potential are yet to be fully understood. End_of_Article - Last_Page 496------------

Two Oil Types on North Slope of Alaska--Implications for Exploration

Forty oil samples from across the North Slope of Alaska have been analyzed by the U.S. Bureau of Mines and the U.S. Geological Survey. Results of these analyses suggest two separate genetic oil types. The first, the Simpson-Umiat oil type, occurs in reservoir rocks of Cretaceous and Quaternary age and includes oil from seeps in the Skull Cliff, Cape Simpson, Manning Point, and Ungoon Point areas, and oils from Wolf Creek test 3, and the Cape Simpson and Umiat oil fields. These are higher gravity, low-sulfur oils with no, or slight, odd-numbered n-alkane predominance and pristane to phytane ratios greater than 1.5. Also, these oils have ^dgr13C values ranging from -29.1 to -27.8 parts per thousand (ppt) and ^dgr34S values from -10.3 to -4.9 ppt. The s cond type, the Barrow-Prudhoe oil type, occurs in reservoir rocks of Carboniferous to Cretaceous age and includes oils from South Barrow gas field, Prudhoe Bay oil field, and the Fish Creek test well 1. Physical properties of Barrow-Prudhoe oils are variable, but in general the oils are medium-gravity, high-sulfur oils with slight even-numbered n-alkane predominance and pristane to phytane ratios less than 1.5. Also these oils have ^dgr13C values of -30.3 to -29.8 ppt and ^dgr34S values from -30.0 to +2.1 ppt. The two types are believed to originate from different source rocks; the Barrow-Prudhoe type may have originated from a carbonate or other iron-deficient source rock, and the Simpson-Umiat type from a siliciclastic source rock. Occurrences of the two oil types when outlined on a map, indicate at least two areas for additional exploration: for the Barrow-Prudhoe type, in stratigraphic traps along and adjacent to the Barrow arch, and for the Simpson-Umiat type, in Cretaceous rocks along the trend between the Simpson and Umiat oil fields and in Cretaceous and Tertiary rocks from Prudhoe Bay field to the William O. Douglas Arctic Wildlife Range.

Two Oil Types on the North Slope of Alaska. Implications for Future Exploration

Forty oil samples from across the North Slope of Alaska have been analyzed by the US Bureau of Mines and the Us Geological Survey. Results of these analyses suggest two separate genetic oil types. The first type, the Simpson-Umiat oil type, occurs in reservoir rocks of Cretaceous and Quaternary age and includes oils from seeps in the Skull Cliff, Cape Simpson, Manning Point, and Ungoon Point areas; the Wolf Creek test well 3, and the Umiat oil field. These are higher gravity, low-sulfur oils with no, or slight, odd-numbered n-alkane predominance and pristane to phytane ratios greater than 1. 5. The second type, the Barrow-Prudhoe oil type, occurs in reservoir rocks of Carboniferous to Cretataceous age and includes ails from South Barrow gas field, Prudhoe Bay oil field, and the Fish Creek test well 1. Physical properties of Barrow-Prudhoe oils are variable, but in general the oils are medium-gravity, high-sulfur oils with a slight even-numbered n-alkane predominance and pristane to phytane ratio of less thon 1. 5. The two types are believed to originated from different source rocks; the Barrow-Prudhoe type may have originated from a carbonate or other iron-deficient source rock, and the Simpson-Umiat type from asiliciclastic source rock. Occurrences of fine two oil types, when outlined on a map, indicate atleast two exploration fairways. The fairway for the Barrow-Prudhoe type is along the Barrow arch, and the fairway, for the Simpson-Umiat type is the area of the best reservoir development for the Nanushuk Group.

Two Oil Types on North Slope of Alaska--Implications for Future Exploration: ABSTRACT

The North Slope of Alaska is a proved petroleum province containing numerous seeps, many small undeveloped oil fields, and the largest oil field on the North American continent, Prudhoe Bay. Genetic relations among oils in the NPRA (National Petroleum Reserve in Alaska), the Prudhoe Bay area, and the Arctic Wildlife Range have important implications for future exploration. Forty-two oil samples from across the North Slope analyzed by the U.S. Bureau of Mines and the U.S. Geological Survey suggest two separate oil types, even though some oils are biodegraded. The first, the Barrow-Prudhoe oil type, is present in reservoir rocks of Carboniferous to Tertiary age and includes oils from South Barrow gas field, Prudhoe Bay oil field, and the Fish Creek 1 test well. Physical properties of Barrow-Prudhoe oils are variable, but in general the oils are medium-gravity, high-sulfur, with a slight even-numbered n-alkane predominance and pristane-to-phytane ratio of less than 1.5. The second type, the Simpson-Umiat oil type, is present in reservoir rocks of Cretaceous to Quaternary age and includes oils from seeps in the Skull Cliff, Cape Simpson, Manning Point, and ngoon Point areas, the Wolf Creek 3 test well, and the Table Umiat oil field. These are higher gravity, low-sulfur oils with no or slight odd-numbered n-alkane predominance and pristane-to-phytane ratios greater than 1.5. The two types probably originate from different sources, the Barrow-Prudhoe type from a carbonate or other iron-deficient source rock, and the Simpson-Umiat type from a siliciclastic source rock. Distribution of the two oil types indicates at least two exploration fairways. The fairway for the Barrow-Prudhoe type is along the Barrow arch, and the fairway for the Simpson-Umiat type coincides with the area of best reservoir development of the Nanushuk Group. End_of_Article - Last_Page 744------------

Alaskan Exploration: ABSTRACT

Alaskan Exploration: ABSTRACT

Oil Production from Frozen Reservoir Rocks, Umiat, Alaska

Abstract The Umiat oil field is in Naval Petroleum Reserve No.4 between the Brooks Range and Arctic Ocean in far-northern Alaska. The Umiat anticline has been tested by 11 wells, six of which produced oil; however, the productive capacity and recoverable reserves of the field are subject to considerable speculation because of unusual reservoir conditions and because several wells appear to have been seriously damaged during drilling and completion. Oil is produced at depths of 275 to 1,100 ft; the depth to the bottom of the permanently frozen zone varies from about 800 to 1,100 ft, so that most of the oil reserves are in the permafrost. Reservoir pressures are estimated to range from 50 to 350 psi, increasing with depth, and the small amount of gas dissolved in the oil is the major source of energy for production. Laboratory tests were made on cores under simulated permafrost conditions to estimate oil recoverable by solution-gas expansion from low saturation pressures. The cores were also tested for clay content and susceptibility to productivity impairment by swelling days and increased water content if exposed to fresh water. The results indicate that oil can be produced from reservoir rocks in the permafrost and that substantial amounts of oil can be produced from depletion-drive reservoirs by a pressure drop of as little as 100 psi below the saturation pressure. Freezing of formation water reduces oil productivity much more than that due to increased oil viscosity. Failure of wells drilled with water-base mud to produce is attributed to freezing of water in the area immediately surrounding the wellbore. Swelling clays apparently contributed very little to the plugging of the wells. Introduction Naval Petroleum Reserve No.4 lies between the Brooks Range and the Arctic Ocean in northern Alaska. The Umiat oil field is located in the southeastern part of the Reserve and is about 180 miles southeast of Point Barrow (the only permanent settlement in the Reserve and the primary supply point for drilling of the wells at Umiat).

Developments in Alaska in 1951

Interest in the petroleum possibilities of Alaska has been increasing since 1944, when the United States Navy began its current exploration program in and near Naval Petroleum Reserve No. 4. Other areas that were investigated in 1951 are the Iniskin Peninsula-Tuxedni Bay area in the Alaska Peninsula-Cook Inlet Mesozoic province, and the Yakataga and Katalla districts in the Gulf of Alaska Tertiary province. No petroleum for commercial use was produced in Alaska in 1951, but a small amount of gas was produced from the Barrow gas field for use by the United States Navy base at Point Barrow. Four geologic parties of the United States Geological Survey and one seismic party of the United Geophysical Company, Inc., were in the field in northern Alaska in 1951. In addition a total of 47,864 feet was drilled in 19 core holes and test wells. Topagoruk test well No. 1 was drilled to the depth of 10,503 feet and bottomed in Lower or Middle Devonian beds. All other test wells or core holes were drilled in Cretaceous rocks except Avak test well No. 1, which drilled into pre-Cretaceous rocks of undetermined age. Further drilling in the Umiat oil field has proved the presence of a sizable oil field. Estimates of recoverable oil range from 30,000,000 to 100,000,000 barrels. Three of the wells drilled in 1951 indicated large quantities of gas in the Umiat and Gubik anticlines. Two geo ogic reports on northern Alaska were published in 1951. The Geological Survey and the General Petroleum Corporation worked in the Katalla-Yakataga area. Preliminary reports on this area were completed by the Geological Survey in 1951 and placed in files available to the public. Applications for land leases in this area have been filed with the Department of the Interior. A Geological Survey party spent about 3 months in the Iniskin Peninsula-Tuxedni Bay area studying the stratigraphy and structure of the Jurassic sediments as well as some of the igneous rocks.