Tectonic evolution and thermal history simulation of Shahejie Formation in eastern Qikou Sag, Bohai Bay Basin

This study focuses on the Shahejie Formation in the eastern part of Qikou Sag of Huanghua Depression, Bohai Bay Basin. Based on the latest three-dimensional seismic and drilling data, the tectonic evolution characteristics and thermal maturation patterns of source rocks in this area were analyzed by balanced cross-section analysis and basin modelling numerical simulation techniques. The results show that the structure of the study area exhibits a parallel or en echelon, pattern, with fault activities controlling differential subsidence and uplift of the strata. The burial-thermal history can be divided into three main stages: the depositional period from Shahejie Formation to the Guantao Formation represents the immature stage; the depositional period from the Guantao Formation to the Minghuazhen Formation marks the low mature stage; and the depositional period from the Minghuazhen Formation to the present represents the mature oil generation stage. For the first member of Shahejie Formation, the shallow layer is in an immature biodegradation stage, and the middle part has entered the immature to low-mature oil stage. For the third member of Shahejie Formation, the upper part is the main oil generation interval, the middle part had formed highly mature condensate oil and gas, and the lower part is dominated by a large amount of gas generation. The results reveal the spatiotemporal evolution patterns of source rocks in the eastern Qikou Sag, providing a key geological basis for regional oil and gas resource evaluation and exploration target optimization.