Origin of gaseous hydrocarbons in subsurface environments: Theoretical considerations of carbon isotope distribution

Genetic correlation of source rocks and natural gas in the Polish Outer Carpathians and Paleozoic–Mesozoic basement east of Kraków (southern Poland)

“…5D) in the Up per Ju ras sic car bon ate and the Up per Cre ta ceous (Cenomanian) sand stone res er voirs (Kotarba, 1992(Kotarba, , 2012Kotarba and Nagao, 2008). This gas was pro duced dur ing In diagrams order of 13 C values for CH 4 , C 2 H 6 ,C 3 H 8 , nC 4 H 10 and nC 5 H 12 is after Chung et al (1988); for key to sampled boreholes see Figure 1 and for abbreviations of stratigraphy of reservoirs and names of lithostratigraphic units see Figure 15 thermogenic pro cesses and mi grated through the fault zones from source rocks in cluded in Mississipian and De vo nian strata (Ta ble 3) and prob a bly also in Lower Pa leo zoic (Si lu rian/Or dovi cian) strata (Fig. 5B).…”

“…20B, B'). Chung et al (1988) and Zou et al (2007) and hy drous py rol y sis ex per i ments re ported by Lewan (2004, 2013) and Kotarba et al (2009) sug gested that a lin ear and a con cave ("dog leg") trend, char ac ter ized by rel atively 13 C-de pleted meth ane com pared to eth ane, and eth ane com pared to pro pane, are in dic a tive of nat u ral gas which was gen er ated from a sin gle source rock and did not un dergo post-gen er a tion al ter ation (e.g. biodegradation or ox i da tion).…”

Origin and fate of deep-sea seeping methane bubbles at Kuroshima Knoll, Ryukyu forearc region, Japan

“…5. The δ 13 C values of C 3 and n-C 4 in the bubbles are larger than the values expected for C 3 and n-C 4 produced from sedimentary organic matter (-20 to -30‰ VPDB ) and also the value for coexisting C 5 (-28.0‰ VPDB ) through thermogenic decomposition (Chung et al, 1988;Mango and Elrod, 1999;Du et al, 2003) or even microbial processes (Oremland et al, 1988;Taylor et al, 2000;Nakagawa et al, 2003). Hence, removal processes for the heavier hydrocarbons accompanying substantial isotopic fractionation must be highly probable for the C 1 -enrichment in the hydrocarbons in the bubbles.…”

“…Regarding thermogenic hydrocarbons, the δ 13 C value for each hydrocarbon reflects the integrated kinetic isotope effect during the cleavage of chemical bonds from parental material. This begins with long-chain organic matter and thus smaller carbon number molecules tend to exhibit lower δ 13 C, with there being a reverse correlation with the reciprocal of the carbon number (Chung et al, 1988;Mango and Elrod, 1999;Du et al, 2003) as shown by the dotted arrow in Fig. 5.…”

Origin and Filling Model of Natural Gas in Jiannan Gas Field, Sichuan Basin, China

“…This observation for the secondary cracking of oil and gas is consistent with the geochemical characteristics of gaseous alkanes with high dryness coefficients and high carbon isotope values, and containing CO 2 from thermal decomposition of carbonates. The sapropelic organic matter was found to be composed of long-chain lipids with homogeneous carbon isotopes enriched in 13 C, and the carbon isotopic compositions of gaseous alkanes have a relationship with their carbon numbers (Chung et al, 1988). Although the natural gases in the Jiannan gases field were sourced from the marine sapropelic organic matter, the convex pattern of carbon isotopic compositions of gaseous alkanes with their carbon numbers in the Jiannan Gas Field is observed , i.e.…”