Geochemical characteristics and hydrocarbon generation potential of the first member of Shahejie Formation (E(2)s(1)) source rocks in the Dongpu Depression, East China

摘要

The Dongpu Depression, containing huge amounts of hydrocarbons, is a typical petroliferous province in the Bohai Bay Basin, east China. As one set of the main source rocks, the first member of Shahejie Formation (E(2)s(1)) shows huge exploration potential with approximately 0.83 x 10(8) t resources remaining to be discovered. However, the geochemical characteristics and thermal evolution history of E(2)s(1) source rocks have still not been determined. In this study, the sedimentary features were firstly analysed based on the geological data. Then the organic matter abundance, kerogen type, and thermal maturity of E(2)s(1) source rocks in the present day were evaluated according to the Rock-Eval pyrolysis, micro-components of kerogen, total organic carbon (TOC), and vitrinite reflectance analysis. Furthermore, the evolution of thermal history and hydrocarbon generation was determined using the PetroMod procedure. The results show that dark mudstones and salt rocks were well developed in E(2)s(1), which are propitious for organic matter to grow and preserve. E(2)s(1) source rocks contain abundant organic matter and moderate to good generative source rock potential. E(2)s(1) source rocks mainly consist of Type II kerogen and have entered early to maturation stage for hydrocarbon generation. Due to the limited buried depth, E(2)s(1) source rocks only attained lower thermal maturity and generated finite hydrocarbons. The initial rapid subsidence and the second rift after uplift erosion resulted in the higher geo-temperature at the end of E(3)d and the present day. Corresponding to the geo-temperature evolution, there are two stages of hydrocarbon generation for E(2)s(1) source rocks: The first stage was in the late E(3)d period, and the late stage was from the late Neogene to the present day. Moreover, the hydrocarbon generation rate and quantity of the late stage are much higher than the first stage, indicating the major hydrocarbon generation stage. Due to the limited