Geochemical characteristics and genetic types of natural gas in the Changxing-Feixianguan Formations from the Yuanba Gas Field in the Sichuan Basin, China

Xiaoqi Wu, Guangxiang Liu, Quanyou Liu, Jingdong Liu, Xiaoyu Yuan
2016 Journal of Natural Gas Geoscience  
The Yuanba Gas Field is a large gas field in the marine strata with the largest burial depth in China up to date. The studies performed on the mentioned gas field have achieved significant progress made possible by determining the characteristics of reef flat reservoirs in the marine strata and the main controlling factors of hydrocarbon accumulation. However, there is no consensus on the origin of natural gases stored in the reservoir in the Changxing-Feixianguan Formations in the Yuanba and
more » ... in the Yuanba and its adjacent area. The study on geochemical characteristics indicates that natural gases in the reservoir in the Changxing-Feixianguan Formations in the Yuanba Gas Field are mainly composed of alkane gases which are dominated by methane with dryness coefficients generally higher than 0.995. The CO 2 and H 2 S display an average content of 8.55% and 6.47%, respectively. The d 13 C 1 and d 13 C 2 values are from À31.2‰ to À27.9‰, and from À29.9‰ to À25.0‰, respectively, displaying the positive carbon isotopic series. The d 13 C CO2 values are generally higher than À8‰, and the dD 1 values are from À156‰ to À107‰. The identification of gas origin and gasesource correlation indicate that the natural gases reservoired in the Changxing-Feixianguan Formations in the Yuanba Gas Field have been altered by thermochemical sulfate reduction, and they are mainly composed of oil cracking gases derived from the secondary cracking of oil generated by the sapropelic-prone source rocks in the Permian Longtan Formation. The CO 2 in the gas pools are mainly inorganic and were derived from the interaction between the acidic fluid and carbonate reservoirs.
doi:10.1016/j.jnggs.2016.09.003 fatcat:k7sljzcmm5gu5bt4tfvpm2irh4