Microbial Origin of Australian Coalbed Methane

Biogenic methane in shale gas and coal bed methane: A review of current knowledge and gaps

“…For example, carbon isotopic differences between CH 4 and CO 2 (δ 13 C CO 2 −CH 4 ) can be helpful to understand gas origin (Strąpoć et al, 2011b): thermogenic process are characterized by low δ 13 C CO 2 −CH 4 determined by high temperatures; conversely, low-temperature microbial enzymatic process determine a 13 C enrichment in residual CO 2 (Conrad and Klose, 2005). In mixtures of thermogenic and biogenic gases, δ 13 C CO 2 −CH 4 can be more suitable than the absolute value of δ 13 C for discriminating gas origin (Smith and Pallasser, 1996;Strapoć et al, 2007). Three diagnostic geochemical variables were identified by Martini et al, (2008): (i) alkalinity and δ 13 C of dissolved inorganic carbon (DIC) in the coproduced water, (ii) δ 2 H of CH 4 and coproduced water and (iii) δ 13 C of CO 2 .…”

“…The relationship between carbon isotope signature of CH 4 and CO 2 (δ 13 C CO 2 − CH 4) could be a better indicator of the extent of methanogenesis than the methanogenic pathway (Brown, 2011;Hamilton et al, 2015Hamilton et al, , 2014Strapoc et al, 2007). The typical δ 13 C CO 2 − CH 4 range for microbial CO 2 -reduction to methane is of 60-80% (Smith and Pallasser, 1996). This carbon isotopic difference arises from preferential microbial utilization of 12 CO 2 .…”

“…This carbon isotopic difference arises from preferential microbial utilization of 12 CO 2 . As a result, residual CO 2 becomes 13 C-enriched (average δ 13 C CO 2 of about 4.3%) and thus contrasts sharply against CO 2 in thermogenic gases with δ 13 C values of around 20% (Smith and Pallasser, 1996).…”

Quantifying emissions of methane derived from anaerobic organic matter respiration and natural gas extraction in Lake Erie

“…Fossil fuel CH 4 produced by high pressure and temperature alteration of organic matter retains isotopic signatures similar to the original plant material, with d 13 C and d 2 H values ranging from 250& to 230& and 2300& to 2150&, respectively. Conversely, isotopic discrimination during anaerobic organic matter degradation leads to depleted isotope ratios in biogenic CH 4 relative to the substrate, with d 13 C and d 2 H values from 263& to 253& and 2350& to 2250&, respectively (Whiticar 1999;Townsend-Small et al 2012, and d 13 C of CH 4 derived from biogenic carbonate reduction can be even more depleted (Smith and Pallasser 1996;Kirk et al 2015). Microbial oxidation of CH 4 in oxygenated waters results in enrichment of both 13 C and 2 H in remaining CH 4 (Whiticar 1999).…”

Gas geochemistry and hydrochemical analysis of CBM origin and accumulation in the Tucheng syncline in western Guizhou Province

“…Many leading scholars took δ 13 C-CH4=-55‰ as the boundary between thermogenic and biogenic methane and concluded that δ 13 C-CH4<-55‰ pointed to biogenesis (Clayton, 1998;Rice, 1993;Scott et al, 1994), whereas Smith and Pallasser (1996) considered that the δ 13 C-CH4 value of biogenic methane can reach -50‰. The distribution of δ 13 C-CH4 values in the Huaibei coalfield, China, ranges from -75.5‰ to -42.8‰ (Li et al, 2015a), which is lighter than in the Tucheng syncline overall.…”