Geology Faculty Research and Publications

Impact of commercial natural gas production on geochemistry and microbiology in a shale-gas reservoir

Thu, 18 Apr 2013 00:00:00 GMT

Impact of commercial natural gas production on geochemistry and microbiology in a shale-gas reservoir Kirk, Matthew F.; Martini, Anna M.; Breecker, Daniel O.; Colman, Daniel R.; Takacs-Vesbach, Cristina; Petsch, Steven T. We consider the effect that commercial gas production has had on microbiology and water and gas geochemistry in the northern producing trend of the Antrim Shale, an unconventional gas reservoir in the Michigan Basin, USA. We analyzed gas, water, and microbial biomass samples collected from seven wells in 2009 and compared our findings to the result of analyses performed as early as 1991 on samples collected from the same wells. We also examined production records associated with six wells. Water production has decreased sharply over time and is currently at 0.2 to 14.6% of peak levels. While this has happened, the chemical and isotopic composition of gas and water produced from the wells has shifted. The proportion of CO[subscript 2] has increased by as much as 15 mole% while CH[subscript 4] content has correspondingly decreased. Isotopically, the δ[superscript 13]C and δD values of CH[subscript 4] decreased for most wells by averages of 1.3‰ and 9‰, respectively, while δ[superscript 13]C values of CO[subscript 2] increased for most wells by an average of 1.7‰. Alkalinity in the water from each well decreased by 10 mM on average and SO[subscript 4][superscript 2−] content increased from below 50 μM to over 200 μM on average in water from each well with initial values. Microorganisms most closely related to CO[subscript 2]-reducing methanogens were the most abundant group in archaeal clone libraries and SO[subscript 4][superscript 2−] reducers were the most abundant group in bacterial libraries. In contrast, no SO[subscript 4][superscript 2−] reducers were identified in a nucleic acid-based analysis of a sample collected in 2002 from one of the wells we sampled . Our results show that commercial gas production has not only caused chemical and isotopic changes in water and gas in the Antrim Shale but also an increase in the abundance of SO[subscript 4][superscript 2−]-reducing microorganisms, a change that can ultimately have a negative impact on biogenic CH[subscript 4] formation. Processes that can explain these changes include ongoing biogeochemical reactions, groundwater flow, gas desorption, and open-system degassing.

Decline in firing technology or poorer fuel resources? High-temperature thermoluminescence (HTTL) archaeothermometry of Neolithic ceramics from Pool, Sanday, Orkney

Tue, 23 Oct 2012 00:00:00 GMT

Decline in firing technology or poorer fuel resources? High-temperature thermoluminescence (HTTL) archaeothermometry of Neolithic ceramics from Pool, Sanday, Orkney Spencer, Joel Q. G.; Sanderson, David C. W. The Neolithic ceramic assemblage from the multi-period coastal settlement at Pool on the island of Sanday, Orkney is unique because it stratigraphically spans both the earlier round-based (including possible Unstan bowls) and later flat-based (‘Grooved Ware’) traditions. High-temperature thermoluminescence (HTTL) analysis objectively demonstrates that ceramics from the earliest Neolithic layers have been consistently better fired compared to examples from later layers. We suggest two interpretations of these data: either firing technology declined with changing social structures and/or adoption of a different ceramic tradition or that there was greater pressure on fuel resource and management in the later Neolithic. Paleoenvironmental and chronological evidence indicate climatic deterioration in the later Neolithic, which adds further support to an interpretation of a poorer fuel resource at that time. In addition to studies of the HTTL signal, analysis of the ambient temperature modification of the TL signal has potential to support or evaluate dating evidence, and is readily applicable to optically stimulated luminescence (OSL) age data.

Perennial ponds are not an important source of water or dissolved organic matter to groundwaters with high arsenic concentrations in West Bengal, India

Mon, 24 Sep 2012 00:00:00 GMT

Perennial ponds are not an important source of water or dissolved organic matter to groundwaters with high arsenic concentrations in West Bengal, India Datta, Saugata; Neal, Andrew W.; Mohajerin, T. Jade; Ocheltree, Troy; Rosenheim, Brad E.; White, Christopher D.; Johannesson, Karen H.

Hydrological control of As concentrations in Bangladesh groundwater

Fri, 01 Jun 2012 00:00:00 GMT

Hydrological control of As concentrations in Bangladesh groundwater Stute, M.; Zheng, Y.; Schlosser, P.; Horneman, A.; Dhar, R. K.; Datta, Saugata; Hoque, M. A.; Seddique, A. A.; Shamsudduha, M.; Ahmed, K. M.; van Geen, A. The elevated arsenic (As) content of groundwater from wells across Bangladesh and several other South Asian countries is estimated to slowly poison at least 100 million people. The heterogeneous distribution of dissolved arsenic in the subsurface complicates understanding of its release from the sediment matrix into the groundwater, as well as the design of mitigation strategies. Using the tritium-helium (3H/3He) groundwater dating technique, we show that there is a linear correlation between groundwater age at depths <20 m and dissolved As concentration, with an average slope of 19 μg L−1 yr−1 (monitoring wells only). We propose that either the kinetics of As mobilization or the removal of As by groundwater flushing is the mechanism underlying this relationship. In either case, the spatial variability of As concentrations in the top 20 m of the shallow aquifers can to a large extent be attributed to groundwater age controlled by the hydrogeological heterogeneity in the local groundwater flow system.