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Sedimentary basins containing low-rank coals have been a target for coalbed methane (CBM) exploration primarily because of the occurrence of microbially-produced coalbed gas.  The Illinois Basin, for example, has significant volumes of CBM stored in high volatile bituminous coals. The objective of our research project was to reliably predict coalbed gas volumes via comprehensive geochemical and isotopic monitoring. During the three years of the project (including a 1-year no-cost-extension period of the initial 2-year PRF grant) we advanced several related coalbed gas sub-projects and published several papers.  

We repeatedly sampled commercially produced gases from CBM production wells in Sullivan County, Indiana in order to investigate production-related changes in gas characteristics over time. Our sampling matrix currently covers a 52-month monitoring period and is continuing. No significant trends have been detected so far, and the most recent geochemical data of CBM are in agreement with our previous observations (Strąpoć et al., 2007, Organic Geochemistry. 38, 267-287; Strąpoć et al., 2008, International Journal of Coal Geology 76, 98-110). The only difference noticed was for well Templeton #26 monitored from September 2005 to April 2008, where the methane content was 99.9 vol. % in all sampling episodes of 2005, 2006, and 2007, but decreased to 99.0 vol. % in April 2008 (nitrogen was not determined). In turn, carbon dioxide increased from 0.09 vol. % in 2005 to 0.45 vol. % in 2008.  In general, we must conclude that the composition of gas from most monitored wells does not change significantly over the time period of our monitoring. Several wells that we had sampled in previous years ceased producing gas and were capped by the owner. Therefore individual time-series may cover less than 52 months.

We expanded our gas sampling effort into the shale gas from the Devonian New Albany Shale play. Two sampling events targeted about 20 shale gas wells. Overall, the resulting CBM and shale gas compositional and isotopic data demonstrate that no change in gas properties was observed over a period of production time from one to four years. We plan to continue our routine gas sampling and to expand our effort to cover other parts of Indiana.  Our Ph.D. student Ling Gao has adopted some aspects of gas research as part of her dissertation. Selected aspects of our research on shale gas have been summarized in a paper that will be submitted to AAPG Bulletin in October 2009 (Strąpoć et al., in preparation for AAPG Bulletin).

      We have advanced geochemical and isotopic characterization of gases from two monitoring wells and one CO2 injection well in the Illinois Basin. During these analyses we discovered that oxygen from the desorption canisters was consumed by the coal in the gas desorption canister. Our graduate student Hui Jin selected this research as his M.S. project and completed it by July 2009. His research showed that atmospheric O₂ is being consumed in desorption canisters, especially rapidly within the first 24 hours. Because of its rapid physical, chemical and microbiological uptake, the residual O₂ content in canisters cannot serve as a reliable proxy for original air contamination. Our results clearly demonstrate that the presence of the air in the desorption canister contributes to overestimation of the nitrogen content in the desorbed gas. A paper detailing results of this research has been accepted for publication in the International Journal of Coal Geology (Hui et al., in press in International Journal of Coal Petrology).  Hui Jin also presented our results at the American Association of Petroleum Geologists (AAPG) Annual Convention & Exhibition, Energy Minerals Division (EMD) session "Coalbed Hydrocarbons", Denver, June 7-10, 2009.

We studied the dependence of adsorption capacities of methane and CO₂ on the lithotype composition of coal by selecting hand-separated lithotypes from several coal beds in the Illinois Basin. This study demonstrated significant differences in adsorption capacities of individual lithotypes and indicated that the lithotype composition of coal needs to be taken into account when predicting the volumes of methane present in coal, as well as in projections of the amount of CO₂ to be injected and stored in coal beds (Mastalerz et al., 2008).