Hydrocarbon generation and expulsion features of the Upper Triassic Xujiahe Formation source rocks and their controlling effects on hydrocarbon accumulation in the Sichuan Basin, Central China

Understanding the features of the hydrocarbon generation and expulsion of the Upper Triassic Xujiahe Formation (T(3)x) source rocks is important to properly guide petroleum exploration in the Xujiahe Formation in the Sichuan Basin. Based on mass balance, the hydrocarbon generation and expulsion from the T(3)x source rocks are characterized in this paper through a method (i.e., hydrocarbon generation potential index using pyrolysis data) different from that used in previous studies. The threshold and peak of hydrocarbon expulsion are determined to be R-o = 0.9% and 1.15%, respectively. The amounts of hydrocarbon generated and expelled in the T(3)x source rocks are 4,525.5 x 10(8) and 2,420.5 x 10(8) t, respectively. Moreover, three hydrocarbon expulsion regions T(3)x have been identified in the Sichuan Basin. On the basis of the hydrocarbon generation and expulsion features of the source rocks and the distribution of the oil-and-gas reservoirs, the quantitative model of the hydrocarbon accumulation probability under the control of the T(3)x source rock is established via single-factor regression analysis. The predictions obtained through this analysis show that the favourable oil-and-gas exploration areas in the Xujiahe Formation are distributed in the Qionglai, Chengdu, and Deyang regions, as well as in the west of Yilong region. Further, the results show that 78% of the discovered oil-and-gas reservoirs are located in the predicted favourable and relatively favourable oil-and-gas exploration areas.