Water and gas samples were collected from coalbed methane wells and surface coal mines in the Powder River Basin and analyzed for solute chemistry, isotopes, and gas composition to determine timing and source of recharge, nutrient influxes, extent of methanogenesis, and redox conditions. Delta18O-H2O values and hydraulic gradients show recharge to coal beds is principally from the southern basin margin with inputs from the western and eastern margins. Detectable 14C in coal waters indicates they were recharged <50,000 BP. Correlation of deltaD-CH4 and deltaD-H2O values suggests that methane has accumulated since the Late Pleistocene. Nutrient concentrations were low and did not correlate to groundwater recharge sources. Coal gases from the northwestern basin are isotopically-depleted suggesting 'early stage' methanogenesis, whereas coal gases from the central southeastern basin are isotopically-enriched suggesting 'late stage' methanogenesis. Several wells have elevated SO4 and oxygen, which may be due to recent hydrologic changes from groundwater pumping.

Thesis (M.S.)--West Virginia University, 1999. / Title from document title page. Document formatted into pages; contains viii, 87 p. : ill. (some col.), maps (some col.). Includes abstract. Includes bibliographical references (p. 81-87).

In the Powder River Basin of Wyoming, our nation's interest in protecting its cultural heritage collides with the high demand for carbon fuels. "Clinker" deposits dot the basin. These distinctive buttes, created by the underground combustion of coal, are underlain by coal veins; they also provided the main lithic resources for prehistoric hunter-gatherers. These deposits signify both a likelihood of extractable carbon and high archaeological site density. Federal law requires that energy developers must identify culturally significant sites before mining can begin. The research presented here explains the need for and describes a statistical tool with the potential to predict sites where carbon and cultural resources co-occur, thus streamlining the process of identifying important heritage sites to protect them from adverse impacts by energy development. The methods used for this predictive model include two binary logistic regression models using known archaeological sites in the Powder River Basin. The model as developed requires further refinement; the results are nevertheless applicable to future research in this and similar areas, as I discuss in my conclusion.

A study of a 250 ft. (76.2 m) stratigraphic interval that includes the Eocene-age Felix coal of the Wasatch Formation was undertaken in the Powder River Basin of Wyoming to establish a depositional model based on the interrelations of coal-seam geometry, coal maceral composition, and spatial distribution of adjoining rocks. Regional cross sections and maps of major rock bodies were prepared from 147 measured stratigraphic sections and 56 geophysical logs. Trends in maceral and chemical properties within the Felix coal were identified from petrographic and geochemical analyses of 72 coal channel samples. The combined data sets indicate that the thickest portions of the coal are underlain by widespread, interconnected, sandstone-dominated fining-upward sequences (< 50 ft. or 15 m thick over a 300 sq. mi. or 777 sq. km area) whereas areas of thin or split coal are underlain by stacked predominantly fine grained, coarsening-upward sequences (< 50 ft. or 15 m thick). Above the coal, fining-upward sequences are concentrated over thin coal areas and widespread (> 20 mi., 32 km wide) coarsening-upward sequences overlie thick coal areas. Megascopic and petrographic description of the coal indicates that the brightest coal contains the greatest amount of huminite. This type coal occurs in the lowest portion of the seam and directly above clay partings in thick coal areas and in split benches · on the margin of the deposit. The central and upper portion of the seam is predominantly dull, and inertinite percentages increase towards the top of the seam. The deposits below the Felix resulted from north-northwest flowing meandering rivers. Thick peat represented by thick portions of the Felix coal accumulated upon this sandstone-dominated, poorly compactible platform that was free of sediment influx. Areas of thin and split Felix coal, underlain by fine-grained, more-compactible sediments, attracted water-borne elastics that interrupted peat accumulation. The base and split portions of the seam are the remains of predominantly coniferous trees that grew within a nutrient-rich environment, and the duller central and upper portions of the seam indicate oxidation associated with a raised peat deposit. Ash falls and fires during late stages of peat accumulation may have contributed to the demise of the swamp. After vegetation died large lakes formed and were subsequently filled by crevasse deposits from streams. The final phase of compaction of the fine-grained lake sediments and the thick underlying peat attracted anastomosed alluvial channels.

Natural gas is an important transitional energy source to replace more carbon intensive coal combustion in the face of climate change and increasing global energy demands. A significant proportion of natural gas reserves (~20%) were recently generated by microorganisms that degrade organic-rich formations (i.e. coal, shale, oil) in-situ to produce methane. Recent studies have shown that these microbial communities may be potentially stimulated to generate more methane to extend the lifetime (~10 years) of existing biogenic gas wells. This dissertation investigates how microbial coalbed methane (CBM) systems are impacted by geochemical conditions, microbial community composition, and groundwater recharge. The first study is a review and synthesis of existing basic research and commercial activities on enhancement of microbial CBM generation, and identification of key knowledge gaps that need to be addressed to advance stimulation efforts. The second study couples water and gas geochemistry with characterization of microbial communities in coalbeds in the Powder River Basin (PRB), Wyoming to investigate the influence of microbiology on water and gas geochemistry. Geochemistry results indicated that nutrients are likely source in situ from coal, and that all sulfate must be removed from the system before methanogenesis will commence. Increased archaeal (i.e. methanogens) diversity was observed with decreasing sulfate concentration, while sulfate reducing bacterial communities were different in wells with high sulfate concentrations (sulfate reducing conditions) when compared to wells with low sulfate concentrations (methanogenic conditions). The third study uses noble gases to constrain the residence time of groundwater associated with CBM in the PRB. Measured diffusional release rates of 4He from PRB coals were ~800 times greater than typical rates observed in sandstone or carbonate aquifers, and measured 4He values far exceeded expected values from in-situ decay of U and Th. Groundwater 4He residence times ranged from <1 to ~800 years using the measured diffusion rates versus ~130 to 190,000 years using a standard model. Coal waters with the longest residence time had the highest alkalinity concentrations, suggesting greater extents of microbial methanogenesis, although there was no relationship between groundwater "age" and methane concentrations or isotopic indicators of methanogenesis. Constraining the relationship between microbial activity (e.g. mechanisms of coal biodegradation and methane generation), environmental geochemical conditions, and groundwater flow is important to better understand subsurface hydrobiogeochemical processes and to ensure the success of future projects related to stimulation of microbial CBM.

As an effort to gain a better understanding of the processes that enable and sustain coal bed methanogenesis in the western Powder River Basin, a steady-state groundwater flow model using MODFLOW 2005 was constructed. The model covers the middle Tongue River Watershed of north-central Wyoming and southeastern Montana and is comprised of five heterogeneous layers. The model is designed to determine the location of recharge and quantify the volume and velocity of groundwater fluxes to, from and within methanogenic coal beds. Analysis of the model's results indicate a groundwater regime dominated by horizontal flow, with little hydrologic connection between the methanogenic coal beds and the near-surface aquifers and streams. The model predicts only 3.88 cubic feet per seconds (cfs) or 2.17 percent of the total steady state flux within the modeled domain percolates downward to potentially reach the methanogenic coal beds. Most of this downward flux is predicted to occur at the base of the Bighorn Mountains. Additionally, the model predicts that the transit time to and resultant groundwater age within the methanogenic coal beds in the study area is on the order of thousands of years (predicted minimum age of 8,967 years).

Thesis (MS)--Montana State University--Bozeman, 2008. / Typescript. Chairperson, Graduate Committee: Alexander V. Zale. Includes bibliographical references (leaves 77-87).

Thesis (Ph.D.) -- University of Montana, 2008. / Title from author supplied metadata. Description based on contents viewed on July 15, 2009. Includes bibliographical references.

Thesis (M.S.)--West Virginia University, 2000. / Title from document title page. Document formatted into pages; contains xii, 156 p. : maps (some col.) Includes abstract. Includes bibliographical references (p. 151-156).

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