--> --> Hydrocarbon Generation and Expulsion Features of the Upper Triassic Xujiahe Formation Source Rocks and Their Controlling Effects on Hydrocarbon Accumulation, Sichuan Basin, Central China

2018 AAPG International Conference and Exhibition

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Hydrocarbon Generation and Expulsion Features of the Upper Triassic Xujiahe Formation Source Rocks and Their Controlling Effects on Hydrocarbon Accumulation, Sichuan Basin, Central China

Abstract

The quantitative study of hydrocarbon generation and expulsion of the Upper Triassic Xujiahe Formation (T3x) in Sichuan Basin is relatively weak. As yet, exploration for favorable exploration zones in T3x in Sichuan Basin has been less than satisfying to petroleum prospectors. According to the principle of mass balance, the hydrocarbon generation and expulsion of source rocks of the Xujiahe Formation are characterized with a novel method, hydrocarbon generation potential index, using the pyrolysis data. The hydrocarbon expulsion threshold is determined to be Ro = 0.9% and the peak of hydrocarbon expulsion is determined to be Ro = 1.15%. The hydrocarbon generation and expulsion amounts of the Xujiahe Formation are 4525.5×10^8t and 2420.5×10^8t, respectively. Besides, there are three hydrocarbon expulsion centers identified of Xujiahe Formation in Sichuan Basin. According to the hydrocarbon generation and expulsion features of source rocks and distribution of oil and gas discovered, the hydrocarbon accumulation probability quantitative characterization model under the control of the Xujiahe Formation source rock is established using single factor regression analysis. After standardization, the intensity of hydrocarbon expulsion shows an exponential characteristic with the increase of hydrocarbon accumulation probability. And the distance of hydrocarbon expulsion has the characteristics of Gamma Distribution (A continuous probability function of statistics) along with the increase of hydrocarbon accumulation probability. Based on the above rules, a quantitative model of oil and gas accumulation probability is established as follow: Fe=4.58Ls^(0.97)×e^(-Ls/0.46)+0.18Ls^(0.97)×e^[0.02qe-(Ls/0.46)]-0.04 (R^2 =0.95, n =41) (Where Fe is the probability of hydrocarbon accumulation, %;qe is the maximum hydrocarbon expulsion intensity, 10^6t / km^2. Ls is distance from hydrocarbon reservoir to hydrocarbon expulsion center after standardization, dimensionless.) Results show that the oil and gas favorable exploration areas in the Xujiahe Formation are distributed in the Qionglai, Chengdu, Deyang, as well as in west of Yilong regions. Production results show that 78% of discovered oil and gas are located in the predicted oil and gas favorable exploration areas and relatively favorable exploration areas.