North Slope Of Alaska Research Articles

Inversion of the planetary boundary layer height from lidar by combining UNet++ and coordinate attention mechanism

The Arctic plays a significant role in global climate, and the planetary boundary layer height (PBLH) is one of the important parameters for studying Arctic climate. The Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) North Slope of Alaska (NSA) atmospheric observatory is an important location for studying the Arctic. However, the weather at the NSA site is complicated and varied. Arctic Haze frequently appears in this region from late autumn to early summer, while low clouds are prone to occur in summer. Meanwhile, due to the consistently low temperatures on the Arctic surface, the frequency of stable boundary layer occurrence is much higher than that in mid-latitude regions. All of these will increase the difficulty of PBLH detection. To address these challenges, we propose a PBLH inversion method based on deep-learning called Coord-UNet++. This method is based on UNet++ and introduces coordinate attention mechanism which can gather features in both horizontal and vertical directions, so it can more effectively capture spatial information in images to cope with complex weather conditions. The training set for the algorithm comes from the micropulse lidar at the NSA site, and the PBLH is labeled by using the microwave radiation profiler at the same site. This algorithm can achieve accurate inversion of the PBLH in complex weather conditions such as cloudy, haze and aerosol layer interference, R2 reaches 0.87, and it performs well in long-term inversion, with much higher stability and accuracy than traditional methods.

Experimental investigation of hybrid enhanced oil recovery techniques for Ugnu Heavy Oil on Alaska North Slope

The Alaska North Slope (ANS) is endowed with a substantial reservoir of heavy oil, estimated at 12–18 billion barrels, primarily concentrated within the Ugnu reservoirs. These deposits, situated at depths ranging from 2,000 to 4,000 feet, lie in close proximity to the permafrost and have undergone biodegradation, resulting in in-situ viscosities reaching thousands of centipoise. Following the success in recovering the somewhat less heavy, viscous oils through polymer injection, the deposits in Ugnu Formation are garnering significant interest. Although thermal recovery methods are commonplace for heavy oils, applying these methods on ANS is impractical, given the adjacency to continuous permafrost. Therefore, non-thermal hybrid enhanced oil recovery (cEOR) methods, such as solvent (e.g., CO2) and low salinity water (LSW) based, or LSW and polymer-based techniques, emerge as the primarily feasible options for recovering these vast heavy oil resources. This study experimentally investigates, via systematically carried out fluid property and phase behavior tests and a series of sand-pack coreflood experiments, the potential to enhance the recovery of Ugnu heavy oils. The coreflood experiments reveal the synergistic effect of combining liquid-CO2 with LSW to be the most promising approach in this study as a water alternating gas (WAG) process results in the cumulative recovery factor of 83.5%, doubling the recovery obtained by continuous low salinity waterflood. Additionally, the liquid-CO2-LSW WAG process demonstrated an additional benefit for CO2 storage, with about 25% of the pore volume of the liquid-CO2 injected being sequestered at the end of the injection process. This significant recovery improvement is attributed to a substantial reduction of oil viscosity upon contact with the liquid CO2 during the soaking period, with a reduction of up to 95% of the original oil viscosity. Meanwhile, in-situ emulsion generation was observed in the oil produced from the continuous LSW flooding. This was also evident by the increased differential pressure across the sand-pack compared to that of the liquid-CO2 alternating LSW process. The promising results of this study indicate significant potential for liquid-CO2 alternating LSW injection as an effective cEOR technique for Ugnu heavy oils.

Frozen no more, a case study of Arctic permafrost impacts of oil and gas withdrawal

Approximately 8100 km2 of Alaska are leased to the oil and gas industry for exploration and extraction. According to industry estimates, subsurface expansion from these leases could cover up to 130.2 km2 per pad. As industrial oil extraction activities increase across the thawing Alaskan permafrost, impacts on the permafrost environment will include rapid thaw, increased hydrological flux, and the release of climate warming greenhouse gases. Here, we use remote sensing and field observations to provide a first-order comparison of the direct impacts to the permafrost tundra from oil well pads, and the long-term consequences of a legacy oil pads on the warming North Slope of Alaska. We find that oil well pads on the permafrost accelerate permafrost degradation and persist despite remediation.

Artificial intelligence for predicting arctic permafrost and active layer temperatures along the Alaskan North Slope

AbstractClimate change in Arctic regions poses a threat to permafrost stability, potentially leading to issues such as infrastructure damage, altered ecosystems, and increased greenhouse gas emissions. The challenge of monitoring permafrost temperatures and identifying critical environmental factors is accentuated by the scarcity of subsurface thermal data in remote Arctic locales. To alleviate this lack of soil thermal data we set out to combine in situ observed soil temperatures with MERRA-2 reanalysis data and Machine Learning (ML) to develop local and season-specific subsurface soil temperature predictions in Alaska. First, reanalysis features are selected based on surface energy budget physics. Coupled with Julian calendar dates, reanalysis features are preprocessed and then fed to the ML prediction model. We conducted a series of computational experiments and tested the results against performance benchmarks to determine the optimal prediction models, length of look-back period of model inputs, and the training set size. Six conventional ML models (e.g., GBDT, RF, SVR) and five statistical baselines (e.g. ARIMA) using in situ time series of soil temperature data ranging from 0 - 1 m depth are considered for the prediction task. The models are trained using in situ soil temperatures at depths between 0 and 1 m, spanning 16+ years, from field sites at Deadhorse and Toolik Lake, Alaska. All prediction performances are assessed using root mean squared error (RMSE) and mean absolute error (MAE). Results show that locally trained ML models can estimate shallow soil temperatures with an average error of $$RMSE=1.308^{\circ }$$ R M S E = 1 . 308 ∘ C.

Long-Term Distributed Temperature Sensing Monitoring for Near-Wellbore Gas Migration and Gas Hydrate Formation

Summary Well integrity monitoring has always been a critical component of subsurface oil and gas operations. Distributed fiber-optic sensing is an emerging technology that shows great promise for monitoring processes, both in boreholes and in other settings. In this study, we present a case study of using distributed temperature sensing (DTS) technology to monitor a cemented and plugged well in the Alaska North Slope (ANS). The well was drilled as part of a long-term gas hydrate study, and the downhole DTS data were recorded over a period of approximately 2 years. By applying a temporal gradient and removing instrument instability noise, we reveal subtle (<0.001°C/h) thermal anomalies, which are characterized by brief warming periods followed by longer cooling periods at discrete depths along the borehole. The observed coherent events show an upward trajectory from deeper formations into the overlying permafrost interval, with the thermal anomalies concentrated in relatively coarse-grained sandstone layers. We also observe that the upward migration rate of the DTS anomalies varies with formation lithology and that there is a spatial and temporal correlation between the subsurface events and measured wellhead annular pressures. We interpret that the observed warming events represent the exothermic process of gas hydrate formation that is occurring in association with the upward migration of gas outside the well casing, and this interpretation is confirmed by numerical simulations. These observations demonstrate the ability of suitably processed DTS data to detect subtle processes and highlight the value of DTS technologies for wellbore integrity monitoring.

Thermokarst landscape exhibits large nitrous oxide emissions in Alaska’s coastal polygonal tundra

Global atmospheric concentrations of nitrous oxide have been increasing over previous decades with emerging research suggesting the Arctic as a notable contributor. Thermokarst processes, increasing temperature, and changes in drainage can cause degradation of polygonal tundra landscape features resulting in elevated, well-drained, unvegetated soil surfaces that exhibit large nitrous oxide emissions. Here, we outline the magnitude and some of the dominant factors controlling variability in emissions for these thermokarst landscape features in the North Slope of Alaska. We measured strong nitrous oxide emissions during the growing season from unvegetated high centered polygons (median (mean) = 104.7 (187.7) µg N2O-N m−2 h−1), substantially higher than mean rates associated with Arctic tundra wetlands and of similar magnitude to unvegetated hotspots in peat plateaus and palsa mires. In the absence of vegetation, isotopic enrichment of 15N in these thermokarst features indicates a greater influence of microbial processes, (denitrification and nitrification) from barren soil. Findings reveal that the thermokarst features discussed here (~1.5% of the study area) are likely a notable source of nitrous oxide emissions, as inferred from chamber-based estimates. Growing season emissions, estimated at 16 (28) mg N2O-N ha−1 h−1, may be large enough to affect landscape-level greenhouse gas budgets.

Polymer Solution Preparation, Quality Control, and Produced Fluid Analysis at Milne Point

Summary This paper focuses on solution preparation and quality control activities associated with the Milne Point polymer flood on the North Slope of Alaska. This project uses 10 different polymer injection locations with a variety of skid types and configurations, which had a notable impact on polymer quality control and dissolution operations. Compared with bulk 500-kg to 750-kg polymer bags, silos greatly improved the storage capacity and increased the overall quality of the polymer solutions. Silos required less physical effort when transferring polymer. Polymer hydration skids that were made in-house by the polymer supplier were more reliable and experienced fewer polymer solution quality and startup issues than those that were outsourced. These in-house skids also used a uniform programming software that made it relatively easy to train the operators on new hydration skids. For pumping polymer mother solution, triplex pumps provided the best runtime and were most maintenance-friendly, compared with diaphragm or triple screw pumps. Because of the soluble iron present in the polymer makeup water, nitrogen blanketing was preferred to minimize corrosion and oxidative degradation. Inline static mixers were ineffective in mixing mother solution with dilution water when the mixing occurred close to the wellhead. Mixing the two streams too close to the wellhead led to substantial variations in wellhead viscosity measurements. Dedicating individual pumps for injection into a given well provided desirable flexibility in controlling rates and concentrations of polymer for the well. Monitoring produced salinity and polymer concentration provided useful insights about improved sweep and polymer retention associated with the polymer flood. The observed field behavior was consistent with laboratory studies, indicating a “tailing” phenomenon associated with polymer retention at Milne Point.

North American Circum-Arctic Permafrost Degradation Observation Using Sentinel-1 InSAR Data

In the context of global warming, the accelerated degradation of circum-Arctic permafrost is releasing a significant amount of carbon. InSAR can indirectly reflect the degradation of permafrost by monitoring its deformation. This study selected three typical permafrost regions in North America: Alaskan North Slope, Northern Great Bear Lake, and Southern Angikuni Lake. These regions encompass a range of permafrost landscapes, from tundra to needleleaf forests and lichen-moss, and we used Sentinel-1 SAR data from 2018 to 2021 to determine their deformation. In the InSAR process, due to the prolonged snow cover in the circum-Arctic permafrost, we used only SAR data collected during the summer and applied a two-stage interferogram selection strategy to mitigate the resulting temporal decorrelation. The Alaskan North Slope showed pronounced subsidence along the coastal alluvial plains and uplift in areas with drained thermokarst lake basins. Northern Great Bear Lake, which was impacted by wildfires, exhibited accelerated subsidence rates, revealing the profound and lasting impact of wildfires on permafrost degradation. Southern Angikuni Lake’s lichen and moss terrains displayed mild subsidence. Our InSAR results indicate that more than one-third of the permafrost in the North American study area is degrading and that permafrost in diverse landscapes has different deformation patterns. When monitoring the degradation of large-scale permafrost, it is crucial to consider the unique characteristics of each landscape.

Santonian-early Maastrichtian radiolarian biostratigraphy of the northern mainland coast of Arctic Canada

Forty-six species of radiolarians recovered from the Upper Cretaceous Smoking Hills and Mason River formations in the Northwest Territories represent the first assemblage of this age from mainland Arctic Canada. Four interval zones and two subzones, calibrated to radiometric ages, are proposed based on the lowest and highest occurrence of index radiolarian species. These are 1) the Santonian/early Campanian Kuppelella aff. cayeuxi Zone, 2) the middle Campanian Diacanthocapsa aff. rotunda Zone (subdivided into the Kreuzstella vierkantiga and Lithostrobus borealis subzones), 3) the late Campanian Canadasphaera inuita Zone, and 4) the early Maastrichtian Stichomitra cf. communis-Xitus sp. B Zone. Integration of these radiolarian biozones with previously reported diatom, silicoflagellate, palynological and foraminiferal biozones and new radiometric ages indicate a middle Coniacian-middle Campanian age for the Smoking Hills Formation and a middle Campanian-late Maastrichtian (probably Paleocene) age for the Mason River Formation. The radiolarian assemblages reported here resemble those of the North Slope of Alaska and western Siberia, allowing for biostratigraphic correlations within the Arctic Realm.

3-D Geological Modeling for Numerical Flow Simulation Studies of Gas Hydrate Reservoirs at the Kuparuk State 7-11-12 Pad in the Prudhoe Bay Unit on the Alaska North Slope

3-D Geological Modeling for Numerical Flow Simulation Studies of Gas Hydrate Reservoirs at the Kuparuk State 7-11-12 Pad in the Prudhoe Bay Unit on the Alaska North Slope

Assessments of Arctic Cloud Vertical Structure From AIRS Using Radar‐Lidar Observations

AbstractThe Atmospheric InfraRed Sounder (AIRS) aboard Aqua provides essential long‐term data on vertical cloud fraction, particularly valuable in the Arctic region. This study offers a comprehensive assessment of Arctic vertical cloud fraction derived from AIRS through a comparison with independent ground‐ and space‐based radar and lidar observations. In comparison to the measurements at the North Slope Alaska site, results reveal a significant underestimation of low‐level cloud cover by AIRS, especially for near‐surface clouds, while mid‐ and high‐level cloud fractions show better consistency. In comparison to the satellite‐based product from 3S‐GEOPROF‐COMB, the accuracy varies across different underlying surfaces (land vs. sea) and seasons. AIRS shows significant positive biases in mid‐level cloud fraction over sea surfaces with sea ice concentration below 15%, indicating potential limitations in the cloud retrieval algorithm in regions with large sea ice variations. The issue of low‐level clouds identification is primarily caused by the limited penetrating capability of infrared hyperspectral sensing and the accuracy of preceding surface and atmospheric state products, which diminish the accuracy of AIRS low‐level cloud fraction.

Assessing the Utility of Uncrewed Aerial System Photogrammetrically Derived Point Clouds for Land Cover Classification in the Alaska North Slope

Uncrewed aerial systems (UASs) have been used to collect “pseudo field plot” data in the form of large-scale stereo imagery to supplement and bolster direct field observations to monitor areas in Alaska. These data supplement field data that is difficult to collect in such a vast landscape with a relatively short field season. Dense photogrammetrically derived point clouds are created and are facilitated to extract land cover data using a support vector machine (SVM) classifier in this study. We test our approach using point clouds derived from 1-cm stereo imagery of plots in the Alaska North Slope region and compare the results to field observations. The results show that the overall accuracy of six land cover classes (bare soil, shrub, grass, forb/herb, rock, and litter) is 96.8% from classified patches. Shrub had the highest accuracy (>99%) and forb/herb achieved the lowest (<48%). This study reveals that the approach could be used as reference data to check field observations in remote areas.

Numerical Simulations in Support of a Long-Term Test of Gas Production From Hydrate Accumulations on the Alaska North Slope: Water Production and Associated Design and Management Issues

Numerical Simulations in Support of a Long-Term Test of Gas Production From Hydrate Accumulations on the Alaska North Slope: Water Production and Associated Design and Management Issues

Sediment ballast accelerates sinking of Alaska North Slope crude oil measured ex situ with surface water from Cook Inlet

Oil spilled into the ocean interacts with suspended matter forming aggregates that transport oil into subsurface layers and towards the bottom. We conducted a series of laboratory experiments to explore aggregation of oil with natural phytoplankton assemblages from Cook Inlet, Alaska at three times during a spring bloom. Oil and phytoplankton formed marine oil snow (MOS) that remained positively buoyant with a small fraction of MOS sinking to the bottom of our experimental bottles. Seawater treatments amended with suspended sediments formed oil-mineral aggregates (OMAs) with an oil capacity similar to MOS (∼20% of aggregate area was covered with oil). OMAs accelerated oil sedimentation in our bottles relative to MOS sedimentation underlining the significance of suspended matter as ballast for sinking oil. Our results reveal potential transport mechanisms of oil in Cook Inlet which apply to other coastal systems with high productivity and sediment loads.

Wolverine population density and home range size in Arctic Alaska

AbstractUnderstanding the spatial requirements of exploited wildlife species, including population density and home range size, is important for wildlife management and conservation. Wolverines (Gulo gulo) are hunted and trapped across the Arctic, and are vulnerable to numerous, often interrelated, threats resulting from anthropogenic changes in their environment. Previous population density estimates for wolverines in the Arctic range tenfold, from the lowest to highest available for the species, limiting their utility outside the specific areas and times they were derived. The most recent density estimate in Arctic Alaska, USA, was produced 4 decades ago and was derived from a relatively small study area. We evaluated wolverine population density and home range size across the North Slope of Alaska during 2017–2022 using global positioning system (GPS)‐based collar data and spatial capture‐recapture models. Population density estimates were 2.0 individuals/1,000 km2 (95% credible interval = 1.3–3.5) in 2018 and 2.8 individuals/1,000 km2 (95% credible interval = 1.7–3.5) in 2021. Median home range sizes modeled with autocorrelated kernel density estimators and Ornstein‐Uhlenbeck foraging movement processes were 699 km2 (range = 158–2,895 km2) among 12 females and 2,332 km2 (range = 797–4,699 km2) among 10 males. These population density estimates are nearly 10 times lower than the previous estimate for Arctic Alaska. We recommend incorporating this information into management strategies to ensure sustainable harvest, particularly as the region's remote areas are more efficiently accessed by hunters and are being considered for transportation corridors supporting new industrial development.

Increasing Methane Emissions and Widespread Cold‐Season Release From High‐Arctic Regions Detected Through Atmospheric Measurements

AbstractRising Arctic temperatures pose a threat to the large carbon stores trapped in Arctic permafrost. To assess methane emissions in high‐Arctic regions, we analyzed atmospheric data from Alaska and Siberia using two methods: (a) a wind sector approach to calculate emission changes based on concentration enhancements using wind direction, and (b) an inversion method utilizing a high‐resolution atmospheric transport model. Incorporating data after 2015, we observed a significant rise in methane emissions (0.018 ± 0.005 Tg yr−2 from 2000 to 2021) from Alaska's North Slope, indicating a shift from previous analyses. We find 34%–50% of yearly emissions occurred in the late season (September–December) consistently across multiple years and regions, which is historically underestimated in models and inventories. Our findings reveal significant changes occurring in the Arctic, highlighting the crucial role of long‐term atmospheric measurements in monitoring the region, especially during the cold season.

The Growth and Carbon Sink of Tundra Peat Patches in Arctic Alaska

AbstractRecent amplified climate warming in the Arctic has caused profound changes in terrestrial ecosystems, with the potential for strong feedback on climate change. Arctic tundra landscapes have developed patchy and thin organic soil (peat) layers at the surface that may continue to grow into mature peatlands and become a larger carbon sink under future warming. Here we use paleoecological analyses of multiple soil and peat cores collected from the North Slope of Alaska to document and understand the formation and development histories of tundra peat patches and permafrost peatlands. We find a consistent peat development sequence for peat patches, first from mineral soils to sedge peat during the Little Ice Age, and then to Sphagnum peat during the recent warming with high carbon accumulation rates. These findings suggest that climate cooling is likely critical for the initial peat buildup on tundra soils due to reduced decomposition, whereas climate warming triggers the regime shift into an increased abundance of Sphagnum mosses that are likely central to enhancing their carbon sink capacity. Additionally, peat patches become similar to permafrost peatlands in the vicinity in terms of ecosystem processes and carbon dynamics, and therefore may have developed the same ecohydrological feedback system to maintain their long‐term stability. This study implies that the potential future expansion of peat patches into peatlands may strongly alter the carbon balance of Arctic tundra, supporting the new United Nations Environment Programme's report that calls for incorporating widespread shallow peat into understanding the peatland–carbon–climate nexus.

Measurement-based carbon intensity of US offshore oil and gas production

The United States (US) produces oil and gas from six offshore regions: the North Slope of Alaska, Cook Inlet in Alaska, offshore California, and three Gulf of Mexico (GOM) sub-regions: state shallow, federal shallow, and deep waters. Measurement-based assessment of direct greenhouse gas emissions from this production can provide real-world information on carbon emissions to inform decisions on current and future production. In evaluating the climate impact of production, the carbon intensity (CI, the ratio of greenhouse gases emitted compared to the energy of fuels produced) is often used, though it is rarely quantified with measurements. Here, we complete an observational evaluation of the US offshore sector and present the largest current set of measurement-based CIs. We collected airborne measurements of methane, carbon dioxide, and nitrogen oxides from the North Slope, Cook Inlet, and California and combined with prior GOM results. For Alaska and California, we found emissions agree with facility-level inventories, however, the inventories miss some facilities. The US offshore CI, on a 100 year GWP basis, is 5.7 g CO2e/MJ[4.5, 6.8, 95% confidence interval]. This is greater than double the CI based on the national US inventory, with the discrepancy attributed primarily to methane emissions from GOM shallow waters, with a methane dominated CI of 16[12, 22] for GOM federal shallow waters and 43[25–65] for state shallow waters. Regional intensities vary, with carbon dioxide emissions largely responsible for CI on the North Slope 11[7.5, 15], in Cook Inlet 22[13, 34], offshore California 7.2[3.2, 13], and in GOM deep waters 1.1[1.0, 1.1]. These observations indicate offshore operations outside of the GOM in the US have modest methane emissions, but the CI can still be elevated due to direct carbon dioxide emissions. Accurate assessment of different offshore basins, with differing characteristics and practices, is important for the climate considerations of expanded production.

Use of resistivity and density borehole image logs to identify and distribute facies in the Pikka unit — A case study from the Nanushuk Formation, North Slope, Alaska

Over the past few decades, the North Slope of Alaska has yielded several major hydrocarbon discoveries in the deltaic topsets of the Brookian Nanushuk Formation. Together, the Nanushuk topsets and genetically related foreset and bottomset beds of the Torok Formation comprise part of a giant clinothem system that prograded across the Colville Foreland Basin during the lower Cretaceous (the Aptian through the Cenomanian). The Nanushuk Topset Play contains stratigraphically trapped hydrocarbons within multiple fairways trending roughly north to south along the basin’s extent. Inside the Pikka Unit, the Nanushuk Formation represents a shelf-edge delta and attached shoreface system, defined primarily from sedimentological interpretations of conventional cores integrated with 3D seismic reflection data and well-log motifs. In this study, we build a structural and stratigraphic framework for the Nanushuk reservoir across the Pikka Unit through integrated observations of the borehole image logs, seismic data, and core. In the described workflow, the boundaries delimiting dip zones interpreted in the wells are correlated to higher order stratigraphic cycles within the Nanushuk clinothem zone. These boundaries are observed in seismic profiles and provide the basis of the structural framework. In addition, core facies interpretations are calibrated to CT-scan data to establish each facies character and vertical distribution within the wells. In the absence of core data, core-calibrated borehole images are instrumental in guiding sedimentological and structural interpretations. This extrapolation is dependent on the image log quality and resolution. The calibrated facies interpretations are applied to wells without core data and guided by seismic amplitude interpretation to extrapolate reservoir presence and distribution across the area.

Characterization of the Structural–Stratigraphic and Reservoir Controls on the Occurrence of Gas Hydrates in the Eileen Gas Hydrate Trend, Alaska North Slope

One of the most studied permafrost-associated gas hydrate accumulations in Arctic Alaska is the Eileen Gas Hydrate Trend. This study provides a detailed re-examination of the Eileen Gas Hydrate Trend with a focus on the gas hydrate accumulation in the western part of the Prudhoe Bay Unit. This integrated analysis of downhole well log data and published geophysical data has provided new insight on structural, stratigraphic, and reservoir controls on the occurrence of gas hydrates in the Eileen Gas Hydrate Trend. This study revealed the relatively complex nature of the gas hydrate occurrences in the Eileen Gas Hydrate Trend, with gas hydrates present in a series of coarsening upward, laterally pervasive, mostly fine-grained sand beds exhibiting high gas hydrate saturations. Most of the gas hydrate-bearing reservoirs in the Eileen Gas Hydrate Trend are laterally segmented into distinct northwest- to southeast-trending fault blocks, occur in a combination of structural–stratigraphic traps, and are only partially hydrate filled with distinct down-dip water contacts. These findings suggest that the traditional parts of a petroleum system (i.e., reservoir, gas source, gas migration, and geologic timing of the system formation) also control the occurrence of gas hydrates in the Eileen Gas Hydrate Trend.