Quantitative effect of kerogen type on the hydrocarbon generation potential of Paleogene lacustrine source rocks, Liaohe Western Depression, China

Kerogen types exert a decisive effect on the onset and capacity of hydrocarbon generation of source rocks. Lacustrine source rocks in the Liaohe Western Depression are characterized by thick deposition,high total organic carbon（TOC） content, various kerogen types, and a wide range of thermal maturity.Consequently, their hydrocarbon generation potential and resource estimation can be misinterpreted. In this study, geochemical tests, numerical analysis, hydrocarbon generation kinetics, and basin modeling were integrated to investigate the differential effects of kerogen types on the hydrocarbon generation potential of lacustrine source rocks. Optimized hydrocarbon generation and expulsion（HGE） models of different kerogen types were established quantitatively upon abundant Rock-Eval/TOC/vitrinite reflectance（R_o） datasets. Three sets of good-excellent source rocks deposited in the fourth（Es4）, third（Es3）,and first（Es1） members of Paleogene Shahejie Formation, are predominantly types Ⅰ-Ⅱ1, Ⅱ1-Ⅱ2, and Ⅱ-Ⅲ, respectively. The activation energy of types Ⅰ-Ⅱ2kerogen is concentrated（180-230 kcal/mol）,whereas that of type Ⅲ kerogen is widely distributed（150-280 kcal/mol）. The original hydrocarbon generation potentials of types Ⅰ, Ⅱ1, Ⅱ2, and Ⅲ kerogens are 790, 510, 270, and 85 mg/g TOC, respectively.The Rovalues of the hydrocarbon generation threshold for type Ⅰ-Ⅲ source rocks gradually increase from0.42% to 0.74%, and Rovalues of the hydrocarbon expulsion threshold increase from 0.49% to 0.87%. Types Ⅰ and Ⅱ1source rocks are characterized by earlier hydrocarbon generation, more rapid hydrocarbon expulsion, and narrower hydrocarbon generation windows than types Ⅱ2and Ⅲ source rocks. The kerogen types also affect the HGE history and resource potential. Three types（conventional, tight, and shale oil/gas） and three levels（realistic, expected, and prospective） of hydrocarbon resources of different members in the Liaohe Western Depression are evaluated. Findings suggest that the Es3 member has considerable conventional and unconventional hydrocarbon resources. This study can quantitatively characterize the hydrocarbon generation potential of source rocks with different kerogen types, and facilitate a quick and accurate assessment of hydrocarbon resources, providing strategies for future oil and gas exploration.