Study on Natural Gas Sources and Accumulation Conditions of Sinian Dengying Formation in Hechuan-Tongnan Area, Sichuan Basin

In April 2021, the risky exploration well HS5 deployed in Hechuan-Tongnan area of the Sichuan Basin obtained a high-producing industrial gas flow in Sinian Dengying Formation, showing a greet exploration potential of beach facies gas reservoir in Dengying Formation of this area. This paper presents a comparative analysis of gas components and carbon isotope characteristics of the Dengying Formation based on gas data from typical high and low producing wells in the area, identifies the source of gas, and comprehensively analyzes the accumulation conditions of gas in the Dengying Formation with the distribution of gas source rocks, reservoir and fracture development characteristics. The results show that: (1) The mean values of C1/C2 of gas fractions in high-producing Well HS5 and low-producing Well HS2 are 2846.0 and 609.7, and the mean values of carbon isotope of ethane are −26.3‰ and −33.8‰, respectively, with obvious differences in gas fractions and ethane carbon isotope characteristics (2) The gas from the high-producing HS5 well is presumed to be of mixed origin, the source rocks of the Sinian Doushantuo Formation has an important contribution, while the gas from the low-producing HS2 well is mainly from the hydrocarbon source rocks of Cambrian Qiongzhusi Formation; (3) The distribution of the source rocks of Doushantuo Formation in the high-producing well area matches well, and the unconformity surface is conducive to the development of high quality reservoirs. The accumulation is mainly controlled by the distribution of source rocks, high quality reservoirs and the development of faults. The results of the study are of great significance for the next gas exploration and deployment in the area.