Thermal evolution modeling and present geothermal field of the Lishui Sag of East China Sea Basin

Hydrocarbon source rocks are deeply buried in the Lishui Sag of East China Sea Basin, where drilling wells are rare and encountered only a few oil and gas discoveries. There are hot debates over the hydrocarbon generating capacity of the basin. Careful study has been made for this time to clarify the thermal evolutionary history of source rocks. Starting from drilling wells with measured formation temperature and vitrinite reflectance (Ro) data, using the forward simulation method, and through the correlation between temperature and stratum depth, we extrapolated the results of drilling temperature research to non-well areas. On the basis of restoring lithospheric structure and its evolution history, the regional geothermal field of the Lishui Sag has been systematically established for the first time. The impacts of geothermal field onto source rock evolution are analyzed. Data shows, most of the source rocks at the bottom of Yueguifeng Formation in the lower part of Paleocene are mature and the sub-depression center is partly over-matured; most of the source rocks at the top of Yueguifeng Formation are in the stage of low-maturity and maturity, the sub-depression center is partly high-mature to over-mature; the source rocks at the top of the Lingfeng Formation are immature to low-maturity, and there are mature source rocks at the center of the western sub-depression. According to the analysis of source rock characteristics and evolution, the source rocks in the lower Paleocene Yueguifeng Formation should be the main source rocks for hydrocarbon generation in the Lishui Sag.