Paleo-heat flow and thermal evolution of the lower cambrian Qiongzhusi shale in the Southern Sichuan basin, SW China

The Paleozoic marine shale in the southern Sichuan basin is one of the most favorable fields for current shale gas exploration in China. The paleo-heat flow history of 5 wells in the southern Sichuan basin were reconstructed by using the vitrinite reflectance (RO) data. The heat flow in the Paleozoic was relatively low, but a heat flow peak occurred during the Permian, with a maximum value of 110 mW/m2 in the southwestern area and 70-90 mW/m2 in the southeastern area. After the Triassic, the heat flow gradually reduced to the present 55-65 mW/m2. Based on the thermal history results, the thermal evolution of the Lower Cambrian Qiongzhusi shale were modeled. Due to the difference in burial history and heat flow history, there are differences in the thermal evolution of the Qiongzhusi shale in different regions in the southern Sichuan Basin. In the southeast area, the Qiongzhusi shale began to generate oil during the Silurian, then it experienced a rapid thermal evolution stage and became overmature during the Permian. However, in the southwest area, the Qiongzhusi shale became mature in the Carboniferous period, and it evolved rapidly in the Permian, during which time the RO reached 2.5%. The burial depth of the Qiongzhusi shale in the Leshan-Longnvsi paleo-uplift area was relatively small during the Caledonian period, so the source rocks remained immature during that time. These source rocks didn't begin to generate oil until the Middle-Late Permian, then they began to produce gas during the Triassic and became overmature in the Jurassic. ©, 2015, Science Press. All right reserved.