Powder River Research Articles

Assessing the Future of Oil and Gas Production and Local Government Revenue in Five Western US Basins

Oil and gas production is a major source of public revenue in many US regions, but uncertainty exists over the future of demand for hydrocarbons. We model how oil and gas production and related government revenue change in five western US basins depending on future oil and natural gas prices under three scenarios of climate policy ambition. We find that the Green River and San Juan basins experience production declines across all scenarios, while production in the Bakken, Permian, and Powder River basins are more dependent on prices. Government revenue generally follows the direction of production, but these relationships are not directly proportional. Under the lower price scenarios, revenue declines more steeply than production because it reflects both production and prices, which both decline. Long-term permanent funds, which are in place across all the states we examine, provide an important fiscal cushion for school districts, their primary beneficiary. JEL Classification: H71, H72, H73, O13, Q41, Q48

Coal ash resources and potential for rare earth element production in the United States

The renewable energy industry is heavily reliant on rare earth elements, underscoring the need to develop resources and production. The objective of this work was to estimate coal ash resources and potential for extraction of rare earth elements using data for the US. Data on spatiotemporal variability in coal ash resources and disposition were compiled from various federal databases and rare earth elements levels in ash were compiled from the literature. Results show that ~ 52 gigatons (Gt) of coal were produced in the US (1950–2021). Power plants account for most of the coal use, particularly since 1980. Coal ash (5.3 Gt) represents a mean of 10% of coal by weight, ranging from 6% for subbituminous to 14% for lignite. About 70% of coal ash is potentially accessible for rare earth element extraction (1985–2021) and was disposed in landfills and ponds with the remaining coal ash used onsite or sold. Median values of total rare earth elements are much higher in ashes derived from the Appalachian Basin (median 431 mg/kg) than in the Illinois (282 mg/kg) or Powder River basins (264 mg/kg). Considering the market value of rare earth oxides, potentially accessible ash volumes, and percent rare earth element extraction (30% Appalachian and Illinois Basins; 70% Powder River Basin) results in an estimated $8.4 billion value. This study provides fundamental information on accessible coal ash resources in the US, linkages to coal sources, and preliminary estimates of rare earth element levels for future development within the US.

Public control of coal resources of the United States’ Powder River Basin for a managed decarbonization transition

Abstract The United States (US) has set aggressive targets for reaching a carbon pollution-free power sector by 2035 and a net-zero economy by 2050. Reaching these goals will require both rapid expansion of zero- and negative-carbon infrastructure and a phase-out of unabated fossil fuel infrastructure. New subsidy and regulatory actions focus on eliminating coal emissions at the point of consumption either through carbon capture and storage (CCS) or coal-fired power plant retirement. Yet, these pathways have opposite implications for coal production: CCS is coal intensive, while coal retirement is not. Despite a record of chaotic and harmful transition and significant social scientific research suggesting better outcomes from managed, coordinated decline, these mechanisms rely on uncoordinated private decision making by mine and plant owners. Coal mining has rapidly declined since peak production in 2008. Production has dropped by half; bankruptcies are the norm; and coal mine and power plant host communities have experienced highly disruptive decline as a result of this unmanaged transition. Given this history, we argue the current market-based, plant-driven governance approach could worsen transition challenges, including potentially stranding costly CCS investments. We argue that the US should complement its extensive investments in technology demonstrations with innovative governance demonstrations to facilitate a just energy transition. Specifically, we argue that the Powder River Basin, which is the US’ largest coal basin and consists primarily of federally leased coal, should be brought under public control for managed decline both to meet emissions reduction targets and advance a just energy transition.

Russian olive distribution and invasion dynamics along the Powder River, Montana and Wyoming, USA

The invasive shrub, Russian olive (Elaeagnus augustifolia), is widely established within riparian areas across North America and eastern Europe. Limited information on its distribution and invasion dynamics in northern regions has hampered understanding and management efforts. Given this lack of spatial and ecological information we worked with local stakeholders and developed two main objectives: (1) map the distribution of Russian olive along the Powder River (Montana and Wyoming, United States) as of 2020 with field data and remote sensing; and (2) relate that distribution to environmental variables to understand its habitat suitability and community/invasion dynamics. Field data showed Russian olive has reached near equal canopy cover (18.3%) to native Plains cottonwood (Populus deltoides; 19.1%) and has a broader distribution. At the watershed scale, we modeled Russian olive distribution using field surveys, ocular sampling of aerial imagery, and spectral variables from Sentinel-2 MultiSpectral Instrument using a random forest model (RMSE = 15.42, R2 = 0.64). A statistical model linking the resulting Russian olive percent cover detection map to environmental variables for the entire watershed indicated Russian olive cover increased with flow accumulation and decreased with elevation, and was associated with poorer soil types. We attribute the success of Russian olive to its broad habitat suitability combined with changing hydrologic conditions favoring it over natives. The maps of Russian olive cover along the Powder River and its main tributaries in northern Wyoming and southern Montana revealed regions of the watershed with high and low cover, which can guide landscape-scale management prioritization. This study provides a repeatable Russian olive detection method due to the use of Sentinel-2 imagery that is available worldwide and provides insight into Russian olive’s ecological relationships and success with relevance for management across areas with similar environmental conditions.

Geologic characteristics, exploration and production progress of shale oil and gas in the United States: An overview

We present a systematic summary of the geological characteristics, exploration and development history and current state of shale oil and gas in the United States. The hydrocarbon-rich shales in the major shale basins of the United States are mainly developed in six geological periods: Middle Ordovician, Middle–Late Devonian, Early Carboniferous (Middle–Late Mississippi), Early Permian, Late Jurassic, and Late Cretaceous (Cenomanian–Turonian). Depositional environments for these shales include intra-cratonic basins, foreland basins, and passive continental margins. Paleozoic hydrocarbon-rich shales are mainly developed in six basins, including the Appalachian Basin (Utica and Marcellus shales), Anadarko Basin (Woodford Shale), Williston Basin (Bakken Shale), Arkoma Basin (Fayetteville Shale), Fort Worth Basin (Barnett Shale), and the Wolfcamp and Leonardian Spraberry/Bone Springs shale plays of the Permian Basin. The Mesozoic hydrocarbon-rich shales are mainly developed on the margins of the Gulf of Mexico Basin (Haynesville and Eagle Ford) or in various Rocky Mountain basins (Niobrara Formation, mainly in the Denver and Powder River basins). The detailed analysis of shale plays reveals that the shales are different in facies and mineral components, and “shale reservoirs” are often not shale at all. The United States is abundant in shale oil and gas, with the in-place resources exceeding 0.246×1012 t and 290×1012 m3, respectively. Before the emergence of horizontal well hydraulic fracturing technology to kick off the “shale revolution”, the United States had experienced two decades of exploration and production practices, as well as theory and technology development. In 2007–2023, shale oil and gas production in the United States increased from approximately 11.2×104 tons of oil equivalent per day (toe/d) to over 300.0×104 toe/d. In 2017, the shale oil and gas production exceeded the conventional oil and gas production in the country. In 2023, the contribution from shale plays to the total U.S. oil and gas production remained above 60%. The development of shale oil and gas has largely been driven by improvements in drilling and completion technologies, with much of the recent effort focused on “cube development” or “co-development”. Other efforts to improve productivity and efficiency include refracturing, enhanced oil recovery, and drilling of “U-shaped” wells. Given the significant resources base and continued technological improvements, shale oil and gas production will continue to contribute significant volumes to total U.S. hydrocarbon production.

Insight into the Evolution of the Eastern Margin of the Wyoming Craton from Complex, Laterally Variable Shear Wave Splitting

Abstract Dense seismic arrays such as EarthScope’s Transportable Array (TA) have enabled high-resolution seismic observations that show the structure of cratonic lithosphere is more heterogeneous and complex than previously assumed. In this study, we pair TA data with data from the Bighorn Arch Seismic Experiment and the Crust and lithosphere Investigation of the Easternmost expression of the Laramide Orogeny (CIELO) to provide unprecedented detail on the seismic anisotropic structure of the eastern margin of the Wyoming Craton, where several orogens emerged from nominally strong cratonic lithosphere during the Laramide Orogeny. In this study, we use the splitting of teleseismic shear waves to characterize fabrics associated with deformation in the Earth’s crust and mantle. We constrain distinct anisotropic domains in the study area, and forward modeling shows that each of these domains can be explained by a single layer of anisotropy. Most significantly, we find a fast direction in the southern part of the Powder River Basin, which we refer to as the Thunder Basin Block (TBB), that deviates from absolute plate motion (APM). This change in splitting behavior coincides with changes in other modeled geophysical observations, such as active source P-wave velocity models, potential field modeling, and seismic attenuation analysis, which all show a significant change moving from the Bighorn Mountains to the TBB. We argue that these results correspond to structure predating the Laramide Orogeny, and most likely indicate a Neoarchean boundary preserved within the lithosphere.

Kinetic Model Evaluation of Arsenic and Selenium Sources in Waste Rock of the Powder River Basin, USA

Kinetic Model Evaluation of Arsenic and Selenium Sources in Waste Rock of the Powder River Basin, USA

A Western Pocahontas: Myth, Reality, and Memorialization for Spotted Tail’s Daughter, Mni-Akuwin

Abstract In March 1866, the Sicangu (Brulé) Lakota chief Spotted Tail brought the body of his seventeen- or eighteen-year-old daughter, Mni-Akuwin, to Fort Laramie. She had died somewhere in the Powder River country. Before she died, she had asked her father to bury her among the Whites at the fort. Her subsequent scaffold burial in the post cemetery was an unusual mix of military display, Christian rites, and Lakota traditions; and the events surrounding it became a dramatic episode in the story of Native-White relations and western settlement. Almost 140 years later she was memorialized at the fort, a National Park Service site, as a symbol of racial reconciliation. The story of Mni-Akuwin has been told and retold many times through the years, often as a romantic tragedy comparable to the story of early Jamestown and the much-celebrated Pocahontas. The two Native women had a surprising amount in common, including what we know and don’t know about them, what has been ascribed to their motives, and how they have been championed as defenders of European colonists and non-Native settlers. Indian princess mythology, with its insistence on innocence, purity, romantic purpose, and tragedy, has been vital to the persistence of this view—a perspective that has often put reconciliation in the service of White supremacy, dispossession, and rejection of Native culture. As the Mni-Akuwin story illustrates, reconciliation can be problematic.

Leachate Experiments to Evaluate Weathering of Waste Rock for Backfill Aquifers in Restored Coal Mine Pits, Powder River Basin, USA

Restoration of open-pit mines may utilize waste rock for landscape reconstruction, which can include the construction of backfill aquifers. Weathering and contaminant transport may be different in backfill aquifers compared to the surrounding aquifer because of newly available mineral surfaces and transportable nano- to micro-scale particles generated during mining. Waste rock from the Cordero Rojo open-pit coal mine in the Powder River Basin was exposed to benchtop leachate experiments for 20 weeks at temperatures of 5 °C and 20 °C. Collected leachate was analyzed for Eh, pH, specific conductance, alkalinity, and cation and anion concentrations as unfiltered and 0.45-μm and 0.2-μm filtered concentrations. During the experiment, leachate Eh and pH substantially varied during the first 55 days, which corresponds to a period of high specific conductance (>1000 µS/cm) and alkalinity (>200 mg/L). Correspondingly, anion and cation concentrations were the largest during this early weathering stage, and the filter fractions indicated multiple forms of transported elements. After this early weathering stage, column leachate evolved towards a weathering equilibrium of neutral, oxidizing, and low solute conditions indicated by positive Eh values, pH near 7, and specific conductance <500 μS/cm. This evolution was reflected in the decline and stabilization or non-detection of metal(loid) concentrations reflective of a shift to primarily bulk aluminosilicate weathering when coal- and salt-associated elements, such as arsenic, cadmium, and selenium, were not detected or at minimal concentrations. Over the course of the experiment, the solute trend of certain elements indicated particular weathering processes—cadmium and nanoparticle transport, selenium and salt dissolution, and arsenic and pyrite oxidation. The mining of overburden formations and use of the waste rock for backfill aquifers as part of landscape reconstruction will create newly available mineral surfaces and nanoparticles that will weather to produce solute concentrations not typically found in groundwater associated with the original overburden.

A Review of Current Scheduling and Design Practices in the Powder River Basin

A Review of Current Scheduling and Design Practices in the Powder River Basin

Novel coal char-based cement grout: An experimental study on geotechnical and rheological properties

Coal char, a light and porous coal byproduct, is conventionally used for combustion and gasification, which leads to high carbon dioxide and other air pollutants emissions. In this study, the feasibility of using coal char in cement grout is evaluated. The coal char pyrolyzed at 850 °C is produced from Powder River Basin coal in Wyoming. Effects of char contents (up to 50%) and particle sizes (<300 μm and 300–850 μm) on geotechnical and rheological properties of char-cement grouts are comprehensively investigated. Compared to cement grout, the compressive strength of char-cement grout is 16% higher, and the final setting time is 55% shorter. The addition of coal char effectively reduces the bleeding in grouts without leading to a significant increase in Marsh viscosity. In general, coal char can provide many advantages towards improving engineering performance and broadening application of conventional cement grout.

Characterizing methane emissions from orphaned coalbed methane wells in the powder river basin

In 2018, the U.S. EPA Greenhouse Gas Inventory (GHGI) began including methane emissions from abandoned oil and gas (AOG) wells and estimated that they may constitute up to 4% of total methane emissions from the oil and gas sector. Several studies have shown that these emissions vary by location which introduces regionally dependent uncertainty into inventory estimates. In Wyoming, there are over 1000 wells identified as ‘orphaned’ indicating that they are both abandoned and unplugged, approximately 80% of which are coalbed methane (CBM) wells. In this pilot study, 3-hour measurements of ten orphaned CBM wells were taken to support the characterization of AOG well emission rates in the Powder River Basin (PRB) in Wyoming. The mean methane emission rate measured at these wells was 653 mg CH4/hr with the majority of these wells emitting in the 100-1000mg CH4/hr range. The highest emitting well in the study was measured at 4.53 g CH4/hr. Compared to the GHGI AOG wells emission factor of 10.04 g CH4/hr, these findings suggest that AOG wells emission rate in the PRB are overestimated by national inventory methods. Finally, the addition of AOG well emissions data from this study doubles the number of sampled AOG wells in Wyoming and triples the number of sampled CBM wells in the U.S.

Ecogeomorphic interactions of Russian olives (Elaeagnus angustifolia) and point‐bar morphology along Powder River, Montana, USA

AbstractPoint bars are crucial alluvial features that help sustain meandering river ecosystems. They are influenced by interactions among physical processes and biological components, such as riparian vegetation. Understanding the mechanisms underlying these interactions can inform management decisions. The meandering Powder River in southeastern Montana, USA, provides a valuable study system for fluvial interactions because it has no major human alterations. Riparian stands of non‐native Russian olive trees (Elaeagnus angustifolia) became noticeable after ~50‐year flood in 1978. Fortuitously, 20 channel cross‐sections had been established in 1975 and 1977 and have been surveyed periodically ever since. This temporally extensive dataset was coupled with a spatially extensive dataset of 85 point‐bar cross‐sections derived from high‐resolution LiDAR that enabled evaluation of interactions between Russian olives and point‐bar morphology through time and space. Based on published literature and field observations, we hypothesised that an increase in the width of Russian olive stands would result in (1) a decrease in the overall point‐bar slope, (2) an increase in point‐bar heights and (3) in point‐bar toe‐slopes. The results indicated that point‐bar slopes did decrease with an increase in stand width, supporting the first hypothesis (R2 = 0.87). However, point‐bar heights decreased with an increase in stand width (R2 = 0.63), contradicting the second hypothesis and there was no relation between point‐bar toe‐slopes and stand width (R2 &lt; 0.1). The reverse hypothesis that point‐bar morphology controls Russian olive stand widths makes more biophysical sense. Thus, Russian olive stand width increases as the point‐bar slope and height decrease (R2 = 0.79 and 0.50), which provide a greater area of inundation for colonisation. This study demonstrates that geomorphology is controlling non‐native vegetation colonisation along Powder River, but that the subsequent stabilisation associated with Russian oliveexpansion may in turn upset the critical geomorphic balance between bank erosion and point‐bar aggradation necessary for a stable meandering system.

Microstructural diversity and digestion yields of select bituminous and subbituminous coals as raw material candidates for carbon fiber precursor production

This work investigates the use of coals as raw materials for carbon fiber precursor production as a new alternative to coal utilization. Coal being a highly complex and heterogeneous material with different macerals and minerals complicates this task. Extensive microstructural characterization as well as preliminary digestion studies are performed on three bituminous coals (Herrin and Springfield from the Illinois Basin and the Blue Gem from the Central Appalachians) and one subbituminous coal from the Powder River Basin (Monarch), as raw material candidates. The subbituminous coal was richer in oxygen, lower in sulfur, and had a higher volatile matter yield. Microstructural investigations were performed using X-ray diffraction, X-ray/neutron computed tomography, scanning electron microscopy with energy dispersive spectroscopy, and petrology. Mild solvent extraction studies were conducted using creosote and decant oil as solvents in microreactors. The extraction yield was sensitive to temperature and time (350 to 450 °C between 30 and 120 mins.) for both creosote and decant oil digestions. While the Blue Gem coal had more desirable microstructural properties with less mineral content and cleaner macerals, it had the lowest coal conversion to quinoline soluble ‘liquid’ (of the bituminous coals). The lower coal conversion yield was hypothesized to be connected to the lack of FeS2 which could act as a catalyst when Fe is liberated from the structure under solvent extraction conditions. The Herrin and Springfield coals revealed similar microstructures and coal conversion efficiencies (higher than Blue Gem). These coals were the most promising candidates for further examination from this first approximations study. The subbituminous Monarch coal, however, was deemed less suitable due to poor coal conversion and less desirable microstructures. Additionally, the presented results with combined microstructural data from multiple length scales established a framework necessary for a first approximations study in this new coal utilization approach.

A Geo-Data Science Method for Assessing Unconventional Rare-Earth Element Resources in Sedimentary Systems

Rare-earth elements (REEs) supply raw materials that constitute many of our modern critical infrastructure, defense, technology, and electrification needs. Despite REE accumulations occurring in conventional bedrock and ion-adsorption deposits sourced from weathering of igneous rocks, unconventional host materials such as coal and related sedimentary strata have been identified as promising sources of REEs to meet growing demand. To maximize the potential of unconventional resources such as REE-coal systems, new approaches are needed overcome challenges from mineral systems with no known deposits and areas with sparse geochemical data. This article presents a systematic knowledge-data resource assessment method for predicting and identifying REE resource potential and occurrence in these unconventional systems. The method utilizes a geologic and geospatial knowledge-data approach informed and guided by REE accumulation mechanisms to systematically assess and identify areas of higher enrichment. An assessment of the Powder River Basin is presented as a test case to demonstrate the method workflow and results. The key output is a potential enrichment score map reported with varying confidence levels based on the amount of supporting evidence. Results from the test case indicate several locations with promising potential for different types of coal-REE deposits, demonstrating the viability of the method for exploration and assessment of unconventional REE resources. The method is flexible by design and, with sufficient applicable knowledge and data, can be adapted for assessing critical mineral systems in other sedimentary systems as well.

Pressurized upflow reactor system for the bioconversion of coal to methane: Investigation of the coal/sand interface effect

Microbial generation of coal bed methane (CBM) represents a significant source of natural gas on Earth. While biostimulation has been demonstrated in batch cultures, environmental parameters such as overburden pressure and formation water flow need to be tested at the laboratory scale to understand in situ potential. We designed and constructed a high-pressure (HP) flow-through reactor system that simulates in situ conditions of underground coal seams. Two stainless-steel columns contained coal from the Powder River Basin (PRB), USA, or a coal/sand mixture to represent the interface of coal seams with sandstone layers, which are hypothesized to exhibit higher methanogenesis rates in situ. The system was filled with CBM formation water, inoculated with a methanogenic enrichment from PRB coal beds, and stimulated with algal biomass as a nutrient. The reactors were incubated under pressure (5.4 atm) and flow of CBM water (0.01 mL/min), and control batch cultures were incubated at ambient pressure and without flow (± amendment). Dissolved and headspace methane concentrations were analyzed over time by gas chromatography for 75 days. The pressurized reactors exhibited longer latency periods than ambient pressure controls, but methane production did not reach a plateau phase, which might reflect the impact of scale on the inoculum. The coal/sand reactor exhibited higher methane production than the coal-only reactor, a pattern also observed in the corresponding controls, suggesting an interface effect on methanogenesis. This study indicates that the HP flow test system we designed is well suited for the study of methanogenesis and provides a successful demonstration of CBM generation from the PRB in field-relevant laboratory conditions as a precursor to meso‑scale demonstrations.

Pore-Pressure-Prediction Model Investigates Hydrocarbon Generation

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper URTeC 2021-5410, “A New Pore-Pressure-Prediction Model for Naturally Fractured Shales and Stacked Plays: The Effect of Active Hydrocarbon Generation—A Powder River Basin Case Study,” by Daniel Orozco and Roberto Aguilera, SPE, University of Calgary. The paper has not been peer reviewed. _ The authors introduce a physics-based method for explicit pore-pressure prediction in naturally fractured shale petroleum reservoirs. Failing to account for the actual cause of overpressure leads to underestimation of the pore pressure at depth. This is particularly important in shales that have not yet reached pressure equilibrium because of fluid expansion caused by currently active or recent-in-geologic-time hydrocarbon generation. Background The work flow is tested with data from the Powder River Basin, but it should be extendable to other shales worldwide. The approach should prove particularly useful in those undeveloped plays with limited or no regional experience, as in the case of the Cretaceous La Luna shale in Colombia. The computer code for running the pore-pressure work flow described in the complete paper was written in open-source Python programming language. The script makes extensive usage of different Python libraries. The complete paper includes a substantive section devoted to a discussion of hydrocarbon generation as an overpressure mechanism in shales. Overpressure by fluid expansion in low-permeability rocks occurs when the volume of pore fluids increases with little change in porosity and at a rate that does not allow the effective dissipation of fluids. The fluid-expansion mechanisms include clay dehydration, smectite-illite transformation, hydrocarbon maturation, and oil cracking. The magnitude of overpressure from fluid expansion depends on the rate of volume change, which is rather slow for the burial rates and temperature gradients observed in most basins. It follows that, in unconventional basins that encompass source rocks with high organic content and very low matrix permeabilities, the maturation of kerogen to oil and gas and oil cracking have the potential to create high-magnitude overpressure. An important aspect of overpressuring caused by hydrocarbon generation is that it has the potential to create natural “hydraulic” fractures. The most-likely explanation for the basinwide occurrence of overpressuring in the Rocky Mountains is the thermal generation of oil and gas. Role of the Biot Coefficient Researchers have demonstrated that the Biot coefficient is equal to the quotient of the change in permeability with pore pressure (at constant confining pressure) over the change in permeability with confining pressure (at constant pore pressure). The authors write that previous work indicates that any deformations in fluid-saturated rocks are exclusively the result of variations on the Biot’s (not Terzaghi’s) effective stress. Because effective stress governs rock deformation, it follows that, whatever the mechanism causing the rock deformation, it should be accounted for and properly explained by the inclusion of the appropriate in-situ Biot coefficient. This statement is the cornerstone of the pore-pressure-prediction work flow.

Fluent in War and Peace

This research is an observation of the life and actions of the Lakota Sioux headman, Red Cloud. A consideration of his life provides the observer with an understanding of the Lakota epoch on the northern Great Plains of North America and his role in the continuation of the Lakota people. As Red Cloud ascended the Lakota meritocracy, he led multiple successful sorties against rival Native groups and the American military. These actions included horse raids and combat missions that enforced Lakota supremacy over the modern Dakotas, Northern Nebraska, eastern Montana, and Wyoming. Later in his life, he and other Plains Natives encountered increasing numbers of Euro-Americans in the form of civilian settlers and traders followed by elements of the Federal Government. As tensions built between the Plains Natives and the US, Red Cloud began to actively oppose American intrusions into Lakota land. The crescendo of Red Cloud’s physical resistance was the Fetterman Fight, an action in which Red Cloud and his allies encircled and destroyed a company-sized element of the US Army. Following its defeat, the US proposed peace through the 1868 Treaty of Fort Laramie. To the US, the agreement concentrated the Lakota in southern South Dakota, away from American economic activities. To men like Red Cloud, unfamiliar with concepts of finite containment, the treaty only affirmed their hunting rights and hegemony in the region. However, as waves of new migrants flowed west from their eastern metropoles, it became apparent to Red Cloud that the policy of the Federal Government was the permanent concentration and degradation of the Lakota. Faced with this forlorn reality, Red Cloud led the Lakota on the reservation through a restricted existence. Despite the Federal attempts at the degradation of the tribe, Red Cloud, using pacifist defiance, ensured the Lakota’s survival and the preservation of a large portion of the region he conquered in his youth. It is possible that his choice to surrender on terms favorable to his tribe and the timing of his cessation of combat actions were more important to the survival of the Lakota than the decision of his peers to continue their war with the US. This is evident in the continuation of the Lakota Pine Ridge Reservation based on the agreement between the US and the Lakota following Red Cloud’s victories in the Powder River Region. Although the Reservation was and is a form of human concentration and containment, it was, a relatively safe place for the Lakota when one considers their treatment outside the sphere of Red Cloud’s influence, most notably the massacre at Wounded Knee.

Investigation of enhanced CO2 storage in deep saline aquifers by WAG and brine extraction in the Minnelusa sandstone, Wyoming

Geological CO2 sequestration in deep saline aquifers has been extendedly investigated to reach the goal of carbon neutral as large amount of CO2 can be reduced in a short time. This study investigates the feasibility of water-alternating-gas (WAG) injection and brine extraction on enhancing CO2 storage in a target deep saline aquifer, Minnelusa Sandstone in the Powder River Basin (PRB) of Wyoming. An integrated numerical model is developed to account for four scenarios: (1) CO2 continuous injection (CI) through one injection well, (2) WAG injection through one injection well, (3) CO2 CI through one injection well and brine extraction through one producer, (4) WAG injection through one injection well and brine extraction through one producer. Simulation results suggest that WAG injection and brine extraction corporately make it possible to enhance CO2 injectivity while securing CO2 storage safety. For instance, WAG injection considerably reduces structural trapping contribution while enhances dissolved and residual trapping contributions. As for brine extraction, it can decrease the maximum averaged reservoir pressure by 37% and 22% for CI and WAG injection, respectively. Besides, sensitive analyses of the operational parameters for the fourth scenarios are performed. Results reveal that, when the amount of total CO2 injection has been predetermined, CO2 injection time and rate within each period of WAG should be small whereas it is preferable to have large water injection time and rate. This is to secure desirable dissolved and residual trapping contributions (store CO2 with safety). Sensitive degree results confirm that CO2 injection rate, water injection time, and CO2 injection time of WAG injection exhibit significant effects on CO2 storage whereas the impacts of producer bottom-hole pressure (BHP), water injection rate, and CO2-water injection time are relatively weaker. This study not only sheds light on achieving double-win goal: enhance CO2 injectivity and store CO2 with safety, but also can be a critical reference for other CO2 storage in deep saline aquifers.

Systematic investigation on the effect of particle size on low-rank coal spontaneous combustion under various extrinsic conditions

Understanding the effect of particle size is vital for studying the low-temperature self-heating characteristics of coal. However, the particle size effect within coals with varying self-heating propensities and extrinsic conditions (temperature and humidity) is still unknown. Three types of Powder River Basin coal samples with three particle sizes (<75 µm, 75–212 µm, and >212 µm) were subject to the modified R70 tests under humid oxygen flow of different temperatures and humidity levels. Characteristics parameters, such as peak temperature, the time to reach thermal runaway, the R70 index, and dynamic wetting heat percentage (DWHP) were determined and systematically analyzed. The results demonstrated that the peak temperature of coal was reached faster as the particle size decreased in the original R70 test. The results of modified R70 tests indicated that the self-heating process of low-rank coal was more sensitive to particle size at lower temperatures. Furthermore, the particle size had a more significant impact on the self-heating process of coals with higher self-heating propensity. In the water cutoff experiments, the finer coal particles received a greater catalyzing effect from oxygen, confirmed by the greater experiment time reduction rate. For the contribution of wetting heat, the DWHP revealed that the coarse coal particles and the coals with lower self-heating propensity absorbed relatively more condensation heat, thus their self-heating process was more dependent on the external heat source.