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

Abstract

The chemical and stable isotopic compositions of natural gases from Jiannan Gas Field, Sichuan Basin, China, were investigated to elucidate the origin of the gas and to reconstruct the reservoir filling history. The natural gases in Jiannan Gas Field are dominated by CH 4 with low amounts of non-hydrocarbon (e.g. CO 2 , H 2 S and N 2 ) components. The stable carbon isotope compositions of methane and its homologues vary widely, with an isotope trend of δ 13 C 1 ≥ δ 13 C 2 < δ 13 C 3 . Structural restoration and burial history reconstruction indicated contrasting gas-filling histories for the gas reservoirs. Natural gas in the Carboniferous reservoirs was sourced from oil and gas cracking and thermal decomposition of kerogen in the lower Silurian shale and sealed by Lower Permian shale. Natural gas in the Upper Permian reservoir was derived primarily from Upper Permian mudstone with a minor contribution from Lower Silurian shale. The sulfurbearing gas was probably sourced from Permian marine source rocks and migrated into the Lower Triassic reservoirs along unconformities and faults. Long-distance vertial migration may have caused the loss of H 2 S.

New exploration strategy in igneous petroliferous basins – Enlightenment from simulation experiments

“…Total hydrocarbon productivity values during experiments focused on the post-hydrocarbon relationship indicate that the mature stage of maturation (350–400°C) is associated with a minor contribution of gaseous hydrocarbon productivity to the total hydrocarbon productivity value, whereas the overmature stage of maturation (temperatures >450°C) yields total hydrocarbon productivity values that are dominated by gaseous hydrocarbon productivity. Gaseous hydrocarbon generation also sharply increases at temperatures of >500°C as a result of the cracking of liquid hydrocarbons generated during the mature stage as well as by the cracking of kerogens (Liu, 2015; Liu et al., 2014, 2012b, 2005). The addition of hydrogen gas leads to liquid hydrocarbon cracking and produces more methane (Jin et al., 2007).…”