Identifying thermogenic and microbial methane in deep water Gulf of Mexico Reservoirs

Abstract

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Position-specific distribution of hydrogen isotopes in natural propane: Effects of thermal cracking, equilibration and biodegradation

“…(3) methanogenesis is commonly associated with hydrocarbon biodegradation (sometimes referred to as 'secondary methanogenesis'; e.g., Jones et al, 2008), and compound-specific stable isotope signatures indicate significant microbial input of methane; that is to say, δD and δ 13 C of methane in these samples match a microbial origin in a 'Schoell/Whiticar diagram' (Figure 1; Whiticar, 1999), and δ 13 C of methane has a negative anomaly (compared to δ 13 C trend of C2+ alkanes) in a 'Chung plot' ( Figure A2); and (4) apparent temperatures derived from Δ 18 -clumped isotope measurements of methane are between 30-68 °C (Figure 7), consistent with the reservoir temperatures of these wells (42-59 °C), suggesting that these methanes were formed (or microbially recycled) in situ (see Thiagarajan et al, 2020a). Although microbial methane is often in clumped isotope disequilibrium Wang et al, 2015;Douglas et al, 2016;Young et al, 2017), microbial methane found in marine and/or subsurface environments is usually in or close to equilibrium.…”

“…Left panel: gases with potential microbial methane input and/or hydrocarbon consumption. (See Thiagarajan et al (2020a) and Section 5.4.2 of this paper); Right panel: gases of thermogenic origin.…”

Methanogens Within a High Salinity Oil Reservoir From the Gulf of Mexico

“…Produced water samples were collected from production wells in the Hoover Field in the Hoover-Diana mini-basin located at the intersection of the Alaminos Canyon and East Breaks area of the western United States Gulf of Mexico. These wells are at 1400-1500 m water depth and the Hoover reservoir has a reported temperature of approximately 68 • C (Thiagarajan et al, 2020). Oil and oil-solution gas are hosted in Plio-Pleistocene age reservoirs, and have been previously reported to be sourced from a Tertiary marine source interval (Hood et al, 2002).…”

Fluid seepage on and offshore Western Greece

“…Based upon the molecular and isotopic composition of methane, ethane, propane, and butane (Stahl, 1977;Bernard et al, 1978;Schoell, 1980;Chung et al, 1988;Schoell, 1988;Hunt, 1996;Whiticar, 1999;Milkov, 2011), geological natural gas can be categorized in three main classes microbial (e.g., Thiagarajan et al, 2020) thermogenic (e.g., Etiope et al, 2013a), and abiotic (e.g., Etiope et al, 2013b).…”

“…Several different types of fluids that escape from the seabed have been surveyed and studied: (i) hydrothermal fluids (e.g., Tao et al, 2020); (ii) geological hydrocarbon, methane-rich gas of microbial, thermogenic or mixed (e.g., Thiagarajan et al, 2020) and abiotic origin (Sciarra et al, 2019); (iii) modern microbial (e.g., Deville et al, 2020); (iii) freshwater discharges (Christodoulou et al, 2003;Whiticar, 2002); (iv) porewater escape (Harrington, 1985); (v) gas and oil saturated water and mud discharges from mud volcanoes (e.g., Chen et al, 2020).…”