Browsing by Author "Strapoc, Dariusz"

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Coalbed gas origin and distribution in the southeastern Illinois Basin
([Bloomington, Ind.] : Indiana University, 2010-06-01) Strapoc, Dariusz; Scimmelmann, Arndt; Mastalerz, Maria
Coal seams worldwide contain biogenic methane that in some coal basins forms easily accessible and large amounts of coalbed methane (CBM). Economically important biogenic CBM occurs not only in coals of low rank but also in higher rank coals where uplift and brine dilution initiated microbial methanogenesis. Distributions and compositions of gases in biogenic systems are governed by numerous factors including salinity, microbe-accessible porosity, and coal permeability. In contrast, thermogenic gas systems are primarily controlled by coal rank and depth. Determination of gas origin is, therefore, critical for a successful exploration strategy. This study employs geochemical, stable isotopic, and microbiological techniques to investigate the distribution and the origin of coalbed gases in the southeastern Illinois Basin. Our results suggest that high permeability and shallow (100-250 m) depths of Indiana coals allowed their inoculation with a methanogenic microbial consortia, thus leading to widespread and abundant microbial methane generation along the eastern marginal part of the Illinois Basin. Consequently, high volatile bituminous C Indiana coals with a vitrinite reflectance Ro ~ 0.6% contain significant amounts of coal gas (~3 cm3/g, 96 scf/t) with ≥ 97 vol.% of microbial methane. In contrast, deeper (>300 m) and more mature (high volatile bituminous A) coals in a tectonically active zone in the western Kentucky part of the basin contain gases of distinctly thermogenic origin. Enrichment experiments and phylogeny of the microbial community responsible for generation of coalbed methane in the Indiana part of the Illinois Basin imply that coal organic matter was biodegraded by a complex microbial consortium to form simple molecules, such as H2 and CO2, that fuel methanogenesis. 16S rRNA analyses of both in-situ microbial communities and methanogen enrichments indicate that Methanocorpusculum is the dominant genus responsible for biogenic CBM formation.
Compound Specific Carbon and Hydrogen Stable Isotope Ratios of Coalbed Gases in Southeastern Illinois Basin
(2007-01-12) Strapoc, Dariusz; Schimmelmann, Arndt; Mastalerz, Maria; Eble, Cortland
Coalbed gases and waters from exploratory and production gas wells in the southeastern Illinois Basin were sampled to geochemically assess the origin of coalbed gases, with emphasis on Springfield and Seelyville coal members that are commercially targeted for coalbed methane production. On-line analyses of hydrocarbon gases (methane to butanes: C1, C2, C3, n-C4, i-C4) and CO2 yielded chemical concentrations, Delta-D, and Delta 13C values. The low thermal maturity of Indiana coals (vitrinite reflectance Ro ~ 0.6%) is in agreement with an overwhelmingly biogenic isotopic signature of coalbed gas that has greater than or equal to 96% methane generated via bacterial CO2-reduction. In contrast, thermogenic coalbed gas was generated by the stratigraphically equivalent coalbeds in western Kentucky’s Rough Creek Graben zone where higher maturities of up to Ro ~ 0.8% are reached due to tectonic and hydrothermal activity. No secondary biogenic methane was observed in Kentucky coalbed gases, probably due to greater burial depths and limited recharge of meteoric water. The two differently sourced types of coalbed gases are compositionally and isotopically distinct. Microbial biodegradation of thermogenic C2+ hydrocarbon gases in Indiana coalbeds preferentially targets C3 and introduces isotope fractionation whereby remaining C3 is enriched in heavy hydrogen and carbon isotopes.
Compound Specific Carbon and Hydrogen Stable Isotope Ratios of Coalbed Gases in Southeastern Illinois Basin
(2007-01-12) Strapoc, Dariusz; Schimmelmann, Arndt; Mastalerz, Maria; Eble, Corland
Coalbed gases and waters from exploratory and production gas wells in the southeastern Illinois Basin were sampled to geochemically assess the origin of coalbed gases, with emphasis on Springfield and Seelyville coal members that are commercially targeted for coalbed methane production. On-line analyses of hydrocarbon gases (methane to butanes: C1, C2, C3, n-C4, i-C4) and CO2 yielded chemical concentrations, Delta-D, and Delta 13C values. The low thermal maturity of Indiana coals (vitrinite reflectance Ro ~ 0.6%) is in agreement with an overwhelmingly biogenic isotopic signature of coalbed gas that has greater than or equal to 96% methane generated via bacterial CO2-reduction. In contrast, thermogenic coalbed gas was generated by the stratigraphically equivalent coalbeds in western Kentucky’s Rough Creek Graben zone where higher maturities of up to Ro ~ 0.8% are reached due to tectonic and hydrothermal activity. No secondary biogenic methane was observed in Kentucky coalbed gases, probably due to greater burial depths and limited recharge of meteoric water. The two differently sourced types of coalbed gases are compositionally and isotopically distinct. Microbial biodegradation of thermogenic C2+ hydrocarbon gases in Indiana coalbeds preferentially targets C3 and introduces isotope fractionation whereby remaining C3 is enriched in heavy hydrogen and carbon isotopes.