Thermal history and hydrocarbon source rock evolution in the northwestern Sichuan basin

Buried and thermal history reconstruction by using vitrinite reflectance data of the northwestern Sichuan basin indicats that the erosion thickness on the Mesozoic and Cenozoic unconformity varied from 1000m to 2500m. The maximum paleo-heat flow reached in the early stage of late Permian,which was 100mW/m~2 in the south area and ～70mW/m~2 in the north,and then decreased to present,and the paleo-heat flow at 220Ma was 54mW/m~2 on average.The Lower Permian source rocks came into the oil-generating window in late Permian.In the south,the Lower Permian source rocks experienced high temperature in a short time,so there was only one time of hydrocarbon generation.However,there were more times of hydrocarbon generation in the north.The upper Permian source rocks came into the oil-generating window in Triassic and then reached the oil-generating peak.And there were also two times of hydrocarbon generation in Jurassic and Cretaceous.The evolution of the upper Triassic source rocks is similar to that of the upper Permian.