Prudhoe Bay Region Research Articles

Optimizing the Use of Miscible Injectant at the Greater Prudhoe Bay Fields

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 180420, “Optimizing the Use of Miscible Injectant at the Greater Prudhoe Bay Fields,” by S.X. Ning, SPE, B.S. Jhaveri, E.M. Fueg, SPE, G. Stechauner, J.L. Jemison, SPE, and T.A. Hoang, BP Exploration (Alaska), prepared for the 2016 SPE Western Regional Meeting, Anchorage, 23–26 May. The paper has not been peer reviewed. Miscible injectant (MI) has been used at Prudhoe Bay and its satellite fields for more than 30 years. This paper provides an overview of all enhanced-oil-recovery (EOR) projects in the Greater Prudhoe Bay (GPB) region and presents the process and methodology for MI allocation to these projects and to individual injection patterns. A new approach is used to determine the amount of MI allocated to each project on the basis of predicted marginal MI use per barrel of EOR oil. Introduction The MI-gas EOR process at Prudhoe Bay began in late 1982. In late 1986, the Central Gas Facility (CGF) began operation, enabling the first field-scale EOR project, the Prudhoe Bay Miscible Gas Project (PBMGP), to start in early 1987. Since then, the PBMGP has expanded to more than 170 injection patterns in the main field of Prudhoe Bay. Fig. 1 provides a layout of the oil fields on the North Slope of Alaska. The CGF is a gas-processing plant that makes natural-gas liquids (NGLs) for shipment in the Trans-Alaska Pipeline System and MI for EOR projects. The CGF currently processes an annual aver-age of approximately 7.5 billion scf/D of produced gas to generate approximately 40,000 STB/D of NGL and more than 200 million scf/D of MI. The feed gas comes from three different sources—solution gas from the produced oil, free reservoir gas from the gas cap, and returned MI (RMI) that was previously injected into the reservoir. The total amount of MI produced at the CGF is the sum of the fresh MI (which can be forecast by the GPB full-field simulation model) and the recaptured RMI (which can be forecast by COBRA and process modeling). COBRA is a full-field scale-up tool for predicting MI performance on the basis of type-pattern-simulation-model results. MI gas produced at the Prudhoe Bay CGF is a rich gas composed primarily of carbon dioxide (approximately 21%), methane (approximately 32%), ethane (20%), propane (25%), and a small amount of butane and heavier components (approximately 2–3%). Most of the GPB EOR projects are pattern floods that use a water-alternating-gas (WAG) injection to improve areal and vertical sweep efficiencies.

Numerical simulations of depressurization-induced gas production from gas hydrates using 3-D heterogeneous models of L-Pad, Prudhoe Bay Unit, North Slope Alaska

Gas production potential is estimated using a three-dimensional reservoir model based on gas hydrate deposits located in the Prudhoe Bay region of the Alaska's North Slope. The model incorporates two hydrate-bearing sand units using detailed reservoir geological and structural information obtained from past and recent drilling programs. Geostatistical porosity models, conditioned to log data from 78 wells drilled in the vicinity of the Prudhoe Bay “L-Pad,” were developed, providing 3D heterogeneity in porosity, porosity-dependent hydrate saturation, and intrinsic permeability. The simulations utilize both vertical and inclined wellbores to induce depressurization of the reservoir at a constant bottom-hole pressure. The results show the superior performance of the inclined well design. Average gas production rates during the first five years were ∼6.0 × 104 ST m3/day (∼2.1 MMSCF/day) and ∼2.7 × 104 ST m3/day (∼1.0 MMSCF/day) for incline and vertical wells, respectively. After 30 years 5.3 × 108 − 5.7 × 108 ST m3 (18.6–20.2 BSCF) and 6.2 × 108 − 6.4 × 108 ST m3 (22.0–22.7 BSCF) gas were produced using the vertical and inclined well configurations, respectively. The analysis reveals that 2D reservoir models with homogeneous representations for porosity and hydrate saturation significantly underestimate production potential. The heterogeneity implemented in this work provides complex porous network and preferential pathways for mobile phase flow to a producing well. Consequently, no secondary hydrate formation around a wellbore is predicted in contrast to models that utilize uniform porosity and hydrate saturation distributions.

PREVALENCE AND SPATIO-TEMPORAL VARIATION OF AN ALOPECIA SYNDROME IN POLAR BEARS (URSUS MARITIMUS) OF THE SOUTHERN BEAUFORT SEA

Alopecia (hair loss) has been observed in several marine mammal species and has potential energetic consequences for sustaining a normal core body temperature, especially for Arctic marine mammals routinely exposed to harsh environmental conditions. Polar bears (Ursus maritimus) rely on a thick layer of adipose tissue and a dense pelage to ameliorate convective heat loss while moving between sea ice and open water. From 1998 to 2012, we observed an alopecia syndrome in polar bears from the southern Beaufort Sea of Alaska that presented as bilaterally asymmetrical loss of guard hairs and thinning of the undercoat around the head, neck, and shoulders, which, in severe cases, was accompanied by exudation and crusted skin lesions. Alopecia was observed in 49 (3.45%) of the bears sampled during 1,421 captures, and the apparent prevalence varied by years with peaks occurring in 1999 (16%) and 2012 (28%). The probability that a bear had alopecia was greatest for subadults and for bears captured in the Prudhoe Bay region, and alopecic individuals had a lower body condition score than unaffected individuals. The cause of the syndrome remains unknown and future work should focus on identifying the causative agent and potential effects on population vital rates.

Point Counts Underestimate the Importance of Arctic Foxes as Avian Nest Predators: Evidence from Remote Video Cameras in Arctic Alaskan Oil Fields

We used video cameras to identify nest predators at active shorebird and passerine nests and conducted point count surveys separately to determine species richness and detection frequency of potential nest predators in the Prudhoe Bay region of Alaska. From the surveys, we identified 16 potential nest predators, with glaucous gulls (Larus hyperboreus) and parasitic jaegers (Stercorarius parasiticus) making up more than 80% of the observations. From the video evidence, however, we identified arctic foxes (Alopex lagopus) as the predators in five of six predation events recorded with the cameras. These results indicate that estimated abundances of predators alone may not accurately reflect their true or proportional importance as nest predators. We also found that the identified predators removed all eggs and left the nests intact. Thus, attempts to identify predators solely on the basis of nest remains are not reliable for smaller bird species in this region. We found no evidence that camera-monitored nests were at greater risk of predation or desertion than camera-free nests. Overall, our ability to film predation events was hampered by the brief, highly synchronized breeding season, the harsh climate, and the higher nest survivorship for shorebirds in this region relative to temperate-breeding passerines, which have been the focus of most studies that use camera systems in attempts to identify nest predators at active nests.

Toward Production From Gas Hydrates: Status, Technology, and Potential

This article, written by Technology Editor Dennis Denney, contains highlights of paper SPE 114163, "Toward Production From Gas Hydrates: Current Status, Assessment of Resources, and Model- Based Evaluation of Technology and Potential," by George J. Moridis, SPE, Lawrence Berkeley National Laboratory; Timothy S. Collett, SPE, US Geological Survey; Ray Boswell, US Department of Energy; M. Kurihara, SPE, Japan Oil Engineering Company; Matthew T. Reagan, SPE, Lawrence Berkeley National Laboratory; and Carolyn Koh and E. Dendy Sloan, SPE, Colorado School of Mines, prepared for the 2008 SPE Unconventional Reservoirs Conference, Keystone, Colorado, 10–12 February. The paper has not been peer reviewed. Gas hydrates are a vast energy resource with global distribution in the permafrost and in the oceans. Even if conservative estimates are considered and only a small fraction is recoverable, the size of the resource is so large that it requires evaluation as a potential energy source. This review paper discusses the distribution of natural-gas-hydrate accumulations, the status of the primary international R&D programs, and the remaining science and technology challenges facing commercialization of production. Introduction Gas hydrates are solid crystalline compounds in which gas molecules (referred to as guests) occupy the lattices of ice-like crystal structures called hosts. Hydrate deposits occur in two geographic settings where the necessary conditions of low temperature and high pressure exist for their formation and stability: in the permafrost and in deep ocean sediments. Most naturally occurring hydrocarbon-gas hydrates contain CH4 in overwhelming abundance. Simple CH4 hydrates concentrate methane volumetrically by a factor of 164 when compared to standard-temperature/-pressure conditions. Some modeling suggests that the energy needed for dissociation could be less than 15% of the recovered energy. Natural-gas hydrates also can contain other hydrocarbons (alkanes), but may also comprise lesser amounts of other gases (mainly CO2, H2S, or N2). The full-length paper contains the complete review. Occurrence, Research Activities and Priorities, and Prospective Production Targets Knowledge of the occurrence of in-situ gas hydrates is incomplete and is obtained from both indirect and direct evidence. There are 23 locations with irrefutable evidence of hydrates (direct recovery of hydrate samples): three in permafrost regions and 20 in ocean environments. In permafrost regions, evidence of gas hydrates is provided from two ongoing R&D programs and from analysis of industry 3D-seismic data and data obtained during the drilling and logging of conventional oil and gas wells. The ability to prospect for gas-hydrate deposits by use of these data was demonstrated in the Prudhoe Bay region of the Alaska North Slope. In the marine environment, most data supporting the interpretation of gas hydrates are indirect indicators (such as bottom-simulating reflections) on relatively low-quality 2D-seismic data. However, direct gas-hydrate detection and characterization from marine 3D data have been shown, and the use of four-component ocean-bottom seismic also shows great promise.

Genetic variation and relatedness in grizzly bears in the Prudhoe Bay region and adjacent areas in northern Alaska

Abstract The Prudhoe Bay region of northern Alaska has large oil fields and hunting on adjacent lands, and there are concerns about potential effects on grizzly bears (Ursus arctos) in this region. Because effects on grizzly bear populations may include loss of genetic variation, we assessed the genetic variation and family relationships among grizzly bears in this region as part of a long-term research and monitoring project. We determined genotypes at 14 microsatellite DNA loci for 78 bears from the Prudhoe Bay region from samples collected 1990–2002. The genetic data identified one or both potential parents of 33 offspring. Potential parent–offspring and siblings had pair-wise relatedness indices of approximately 0.5, as expected. The entire sample of related and unrelated bears in the Prudhoe Bay region had a mean pair-wise relatedness index of approximately zero. Approximately 5.3% of the bears had relatedness indices within the range of first-order relatives (parent–offspring or siblings). Genetic d...

Genetic relationships of grizzly bears (Ursus arctos) in the Prudhoe Bay region of Alaska: inference from microsatellite DNA, mitochondrial DNA, and field observations.

Grizzly bears are abundant in the region of the Prudhoe Bay oil fields in northern Alaska. We used field observations and molecular genetic data to identify parent-offspring and sibling relationships among bears in this region. We determined genotypes at 14 microsatellite DNA loci and the cytochrome b gene of mitochondrial DNA (mtDNA) for 36 bears. We identified 17 possible mother-offspring pairs and 8 possible father-offspring pairs. This includes verification of the relationships of 14 mother-offspring pairs identified from field observations. Three additional mother-offspring pairs and all eight father-offspring pairs were determined from genetic and age data. Relatedness coefficients based on numbers of shared alleles between individuals were as expected: approximately 0.50 for parent-offspring and sibling pairs and approximately 0.75 for a father-offspring pair resulting from a father-daughter mating. The level of genetic variation (mean number of alleles per locus = 6.6, mean heterozygosity = 70%) and allele frequencies in grizzly bears in the Prudhoe Bay region are similar to those in other parts of the species' range.

Northern Alaska oil fields and caribou: A commentary

We discuss the status of caribou, Rangifer tarandus, herds relative to oil field development in the Prudhoe Bay region of Alaska. The Central Arctic caribou herd, which spends June and July in and around oil fields in the Prudhoe Bay region, has increased since the inception of oil field development and has demographics similar to those of adjacent herds which are not near oil fields. Although oil field development may impact individual caribou through disturbance or impedance of movements, herd-level impacts of the oil fields are not apparent. Caribou populations characteristically fluctuate dramatically, and differentiating human and non-human impacts is difficult or impossible. The herd is the unit of management, and management objectives are being met. The experience in northern Alaska's oil fields indicates resource extraction and wildlife populations can be compatible when managed properly.

Summer growth patterns of northern Dolly Varden (<I>Salvelinus malma</I>) smolts from the Prudhoe Bay region of Alaska

Summer growth patterns of northern Dolly Varden (<I>Salvelinus malma</I>) smolts from the Prudhoe Bay region of Alaska

Soil Development as an Indicator of Relative Pingo Age, Northern Alaska, U.S.A.

Soils of pingos in the Prudhoe Bay region of northern Alaska (700N, 1480W) were examined to determine if their development could be used to support or nullify a hypothesis of differential age between two morphologically distinct groups of pingos. The two morphological types, one with steep side slopes and small basal diameters (steep-sided) and one with gentle side slopes and large basal diameters (broad-based), have been proposed to represent two different age groups. Steep-sided types are found on landscape surfaces of all ages, always within recognizable thaw-lake basins, and are all presumed to have formed within the last 10 kyr. Broad-based types are found only on pre-Holocene surfaces and never within recognizable thaw-lake basins, leading to speculation that they formed during a previous thaw-lake cycle on the older surfaces. Soils were described and collected from nine localities on each of three steep-sided and two broad-based pingos. Profile development was quantified using an index that compares soil morphology with parent material characteristics. A second index quantified profile anisotropy of various soil properties. Multiple lines of evidence from the pingo soils supports the differential age hypothesis. Broad-based pingos have greater concentrations of clay and iron, lower pH, more developed color, structure, and consistence, and greater profile anisotropy. Absolute pingo ages were estimated by developing regression equations for profile development of temperate soils from the literature and applying these to the pingo soils. The regression resulted in estimated ages of the steep-sided pingos of approximately 5 ky and of broad-based pingos of 14-22 kyr, which are thought to be minimum age estimates.

Intra- and Interannual Variation in the Relative Condition and Proximate Body Composition of Arctic Ciscoes from the Prudhoe Bay Region of Alaska

Abstract Weight and length data collected during the summers from 1984 through 1994 were used to examine the seasonal life history strategy of Arctic ciscoes Coregonus autumnalis collected from Prudhoe Bay, Alaska. Differences in observed and predicted weight were used to determine if condition increases during the summer feeding season when energy reserves are accumulated and decreases during winter when energy reserves are depleted. Data from proximate body analyses of lipid and protein content collected from 1991 to 1993 also were examined. Condition was indexed as residual values generated from a whole population least-squares regression of log e -transformed weight and length data. For data pooled by individual year-classes, we tested the conceptual hypothesis that mean residual value, mean lipid content, and mean protein content increased during summer and decreased during winter. For the 12 year-classes examined, concurrent mean residual values supported our conceptual hypothesis in 61 of 76 instan...

Intra- and Interseasonal Changes in the Relative Condition and Proximate Body Composition of Broad Whitefish from the Prudhoe Bay Region of Alaska

Abstract A relative weight approach was used to test the hypothesis that the condition of broad whitefish Coregonus nasus in the Prudhoe Bay region of Alaska increases during the summer feeding season in conjunction with their increasing lipid and protein contents and decreases during winter as fish consume these energy reserves. The conditions of individual fish collected across 12 summer dissection periods from 1988 to 1993 were indexed in terms of their residual values relative to a single whole-population, least-squares regression of log e (weight) against log e (length). Proximate body analyses of lipid and protein contents collected from individual fish across six dissection periods from 1991 to 1993 were also examined. Data pooled for individual year-classes were used to test for increasing mean residual value, mean lipid content, and mean protein content during summer and for decreasing values of each during winter. Of the 68 cases examined (14 year-classes over 6 years), mean residual value chang...

Growth and Condition of Arctic Cisco and Broad Whitefish as Indicators of Causeway-Induced Effects in the Prudhoe Bay Region, Alaska

Abstract We describe trends in growth and condition of Arctic cisco Coregonus autumnalis and broad whitefish C. nasus in the Prudhoe Bay region of northern Alaska for the period 1985–1989 to evaluate sublethal effects of changes in hydrography induced by building a causeway into the Beaufort Sea. Growth (increase in length) of age-1 and age-2 fish of both species was positively correlated with temperature, which explained 77–92% of the sample variance, Condition (whole wet body weight at a given length) was less correlated with temperature than was growth. However, small broad whitefish, which do not venture far from river mouths, showed a positive association between condition and salinity. Conversely, large broad whitefish, which range away from the rivers, exhibited a negative association with salinity. The foraging range of large broad whitefish may be restricted by high-salinity water masses that, however, may deliver higher-than-normal levels of prey to the habitats near river deltas used by small f...

Pingos of the Prudhoe Bay Region, Alaska

Two distinctive types of small dome-shaped hills occur in the Prudhoe Bay region. One type has small basal diameters, steep side slopes, and occurs primarily in drained thaw-lake basins; the other type consists of mounds of larger diameter and commonly occurs outside modern lake basins. The U.S. Army Cold Regions Research and Engineering Laboratory drilled three of the mounds including one broad-based mound and encountered massive ice in all of them. It is thus likely that all of the steep-sided mounds and at least the larger broad-based mounds are pingos. It is clear that the largest of the broad-based mounds are neither dunes, unmodified remnants, nor highly eroded steep-sided pingos of the type common in the region today. Discriminant analysis of topographic-map data indicates that mean slope and length of the longest axis are the clearest discriminators between the two groups of mounds. The broad-based mounds are limited to older surfaces in the region and are thus likely to be quite old (< 12,000 yr). Explanations for the large size of many of the broad-based mounds and their occurrence outside lake basins will have to await detailed drilling studies.

Pingos of the Prudhoe Bay Region, Alaska

Pingos of the Prudhoe Bay Region, Alaska

Geobotanical Atlas of the Prudhoe Bay Region, Alaska

Geobotanical Atlas of the Prudhoe Bay Region, Alaska

Geobotanical Atlas of the Prudhoe Bay Region, Alaska, the Physics of Glaciers, Quaternary Paleoclimate, Mountains and Man: A Study of Process and Environment

Geobotanical Atlas of the Prudhoe Bay Region, Alaska, the Physics of Glaciers, Quaternary Paleoclimate, Mountains and Man: A Study of Process and Environment

Geobotanical Atlas of the Prudhoe Bay Region, Alaska, by D.A. Walker, K.R. Everett, P.J. Webber and J. Brown

Geobotanical Atlas of the Prudhoe Bay Region, Alaska, by D.A. Walker, K.R. Everett, P.J. Webber and J. Brown

Carboniferous Carbonate Depositional Models, Preliminary Lithofacies and Paleotectonic Maps, Arctic Alaska

Two distinct environmental suites can be delineated for the shallow-marine Carboniferous rocks of Arctic Alaska. One is a marine transgressive suite, typified at its base by a paralic clastic sequence followed by nearshore shales and siltstones, and overlain by spiculitic carbonate rocks. This transgressive clastic-marine carbonate sequence is associated with regional Mississippian transgression. Developed above this is a carbonate platform sequence characterized by very low terrigenous clastic content and shallow-water cyclic carbonate sedimentation. The outer margins of the shelf did not support reef-forming organisms. Carboniferous sedimentation in Arctic Alaska represents a northward marine transgression over an irregular surface with residual stable positive areas. In the northeast, the Sadlerochit high was not submerged until early Chester time. In the west-central foothills region, the Nuka high is a long, linear, east-trending positive area in the subsurface; it may have been the source for the Mississippian feldspathic clastic rocks of the Nuka Formation. The Nuka high may have remained a mildly active positive element during the Mississippian. A northeast-trending negative area, the Canning sag, stretches from the Prudhoe Bay region southwest to the Sagavanirktok River region of the Brooks Range, where there is a 3,000-ft-thick accumulation of shallow-water Carboniferous carbonate rocks. The Lisburne Group, at many outcrops in the Brooks Range, was deposited as a complex of cyclic shallow-water carbonate sediments in an arid or semiarid climate. A typical cycle grades from marine ooid-crinoid grainstone to supratidal microdolomite. Composite cyclic carbonate sequences may be thousands of feet thick in outcrop. Outcrop studies indicate that thick sequences that have been dolomitized by reflux brines may have reservoir qualities in the subsurface of the north slope.

Thermal Model For Roads, Airstrips And Building Foundations In Permafrost Regions

Abstract A thermal model describing the one-dimensional heat conduction in a layered system is developed. Up to ten homogeneous layers, each having different thermal properties porosity, water content and thickness, can be accommodated. A periodic temperature is input for the surface condition. The computed results consist of the depth of the thawed region as a function of time. The layered model is applied to the design of foundations for roads and airstrips in permafrost regions. A sensitivity study was made to find the effect on thaw depth of varying physical properties of the materials used, the geometry of the construction and the surface temperature. The means for extension of the model to building foundation design by modification of the surface boundary condition is presented. Introduction THE DISCOVERY OF OIL in the Prudhoe Bay region of Alaska has focused considerable attention on the engineering problems of developing petroleum production facilities in remote arctic areas. The main source of difficulty is the undesirable thawing of permafrost under such structures as roads) airstrips, buildings and drilling equipment. Subsidence, differential settlement and frost heaving may be expected if the permafrost formation under the structure is allowed to thaw seasonally or permanently(1). In order to guard against such destruction, building sites may be placed on gravel embankments which; in turn, may rest on a thermal insulator as is common in road construction on the arctic tundra(2). In order to insure adequate and economical protection of the underlying permafrost, accurate predictions of the temperature distribution and the depth of thaw under engineering structures become important. It is the purpose of this paper to present a thermal model for calculating the seasonal depth of thaw in a layered medium; it is applicable to general structures where the heat flow is essentially one-dimensional. In this model heat transfer is assumed to be due exclusively to conduction. For pure ice-water mixtures (such as ice on lakes) this assumption is inadequate because of convective effects(3). It is recognized that on a microscopic scale the exact mode of heat transfer in permafrost is likely to be a combination of conductive, convective and radiative processes(4); however, on the basis of soil temperature measurements, Pearce and Gold(5) were able to conclude that "the annual temperature variation in the soil ... is remarkably consistent with the theory of (conductive) heat flow in a one-dimensional semiinfinite medium." Thus, a conduction model may be used with confidence for temperature studies in permafrost. This problem has been investigated by Lachenbruch(6) for a system limited to three layers. Our model and discussion to some extent are parallel to that of Kazemi and Perkins(7). The basic difference, apart from the structures studied, is in the solution algorithm used for solving the heat flow equations. The method proposed here is mathematically sound(8), easy to apply, allows a fine spatial resolution and is quite fast. In fact, the discussion of construction methods for roads and airstrips is based on a parameter study conducted via interactive computer graphics.