Longmaxi shale gas geochemistry in Changning and Fuling gas fields, the Sichuan Basin

Abstract

This paper focuses on Longmaxi shale gas geochemistry and carbon isotopic reversal in Changning and Fuling gas fields through comparative study of shale gas composition and carbon and hydrogen isotopes in North America and Changning and Fuling gas fields. Longmaxi shale gas in Changning and Fuling gas fields exhibits the features of dry gas. Specifically, the average methane (CH 4) content is 98.72 and 98.17%, respectively. The humidity is less than 0.5%. Nonhydrocarbon gases include a small amount of CO 2 and N 2. Extremely heavy d 13 C 1 value, average d 13 C 2 value of À33.3 and À34.6% for Changning and Fuling, and sapropelic organic matter indicate the properties of petroliferous dry gas. Carbon isotopic reversal, i.e. d 13 C 1 >d 13 C 2 >d 13 C 3 , may be caused by combined secondary effects at high maturity and high geotemperature. The reversal may also be related to ethane Rayleigh fractionation and late methane generation by water and transition metals reaction. Geologic setting in these two gas fields may have an impact on carbon isotopes distribution.

Stable carbon isotope systematics of methane, ethane and propane from low-permeability hydrocarbon reservoirs

“…In contrast, the Barnett Shale has reached the oil window with thermal maturities varying from 1.0 to 2.0 of %Ro (Zumberge et al, 2012), and the ∆ 13 CC 1 -C 2 and ∆ 13 CC 1 -C 3 values of its gas are considerably less negative (>-15 ‰ and >-20 ‰, respectively). The maturity in the Clinton/Medina Group ranges from 1.5 to 3.0 %Ro (Repetski et al, 2008) and the Longmaxi Formation in China is highly mature with a %Ro ranging between 2.7 and 3.3 % (Feng et al, 2017). Gas samples from these two reservoirs are characterized by the most positive…”

Geological conditions of coalbed methane accumulation in the Hancheng area, southeastern Ordos Basin, China: Implications for coalbed methane high-yield potential

“…The CBM critical depth is largely controlled by geological structure and in situ stress state, and further supports the formation of the independent superposed CBM systems (Qin et al., 2008a, 2016a). It is of great significance to distinguish the spatial differences in CBM accumulation and discriminate the critical depths of a gas-bearing system to identify the favorable areas or intervals of CBM enrichment (Chen et al., 2017; Feng et al., 2017; Karacan, 2013; Liu et al., 2019; Zhao et al., 2015, 2017). It is also meaningful and necessary to study the role of critical depth on CBM high yields (Chatterjee and Pal, 2010; Chatterjee and Paul, 2013; Guo et al., 2018).…”

Terrestrial heat flow and geothermal field characteristics in the Bide-Santang basin, western Guizhou, South China

“…The present-day geothermal field is significant for coal and CBM exploration and exploitation, geothermal resources prediction, and geological hazard prevention. Present-day geothermal research is focused on the factors controlling the distribution of formation temperature, geothermal gradient, and terrestrial heat flow (Deng et al, 2012; Jiang et al, 2016; Pascal, 2015; Reiter, 2014; Tanikawa et al, 2016) and has recently received considerable attention related to the exploration and exploitation of coal, petroleum, and natural gas (Feng et al, 2017; Isaev et al, 2014; Kuzielová et al, 2017; Li et al, 2017; Liu et al, 2016; Safari et al, 2017). Temperature is one of the primary factors controlling hydrocarbon generation, sediment diagenesis, migration of hydrocarbons, and pore fluids (Nwankwo, 2007).…”