Identification of chief hydrocarbon source rocks in Lishu Fault Depression and their geochemical characteristics

Based on the hydrocarbon generation potential of 4 sets of source rocks developed in the Lishu Fault Depression, the results illustrated that the chief hydrocarbon source layer is K₁sh and the secondary layer is K₁yc; meanwhile, the effective source rocks of K₁h and K₁d formations only developed in some certain areas. We made a cluster analysis to source rock samples (TOC>0.5%) based on more than 20 variables, and the results have shown that the source rock samples can be divided into 4 types and the geochemical characteristics of 4 types of source rocks are different in many respects, such as sedimentary environment, hydrocarbon generation potential, origin of organic matters and maturity stages. Type C and D source rocks have the highest hydrocarbon generation potential and they have good comparability with crude oils. Taking into account the plane distribution of source rocks, type C source rocks mainly distribute in Siwujiazi, Pijia and Sangshutai deep depressions with deep lake facies. Meanwhile, type A, B and D source rocks mainly distribute in Sujiatun sag, Shuanglong sag and Taipingzhuang, Qikeshu, Qinjiatun areas along the basin margins with shallow lake facies, semi-deep lake facies and swamp subfacies within delta plain sedimentary environment.