Changxing Formation biohermal gas pools and natural gas exploration, Sichuan Basin, China

Plain fluvial facies, paralic facies, shallow gentle slope facies on carbonate platforms, platform marginal reef facies, Kailiang trench facies, and north Sichuan western Hubei ocean basin facies are developed in the Permian Changxing Formation and have favorable source-reservoir-seal conditions. To improve the seismic prediction reliability of biohermal anomalies, a recognition mode of biohermal seismic anomalies was established in the late 1990s based on the geological features of known reefs and the corresponding seismic reflection features, and 182 biohermal anomalies were found in eastern Sichuan. Researches on sedimentary facies reveal a platform marginal reef facies from both sides of Kailiang trench to western Hubei, and the seismic anomalies of 36 marginal reefs have been found there. These marginal reefs have large areas and high drill reserves. The facies belt extends to the western margin of the basin. Many point reefs are developed on the slope platform facies, and 146 seismic anomalies of point reefs are found in eastern basin. Point reefs are developed widely in central basin.