Cenozoic tectonic-thermal history reconstruction of the Qinnan Depression, Bohai Basin

Abstract

Objective Tectono-thermal history is important to understand basin evolution and its geodynamic mechanism and is the key question to be solved for source rock maturation study. With the increasing energy demand and difficulty in oil and gas discovery on land, sea basins have gradually become an important alternative for oil and gas exploration and a hotspot of national energy strategy research. The Qinnan Depression, located in the northwest of the Bohai Sea, has good exploration prospects. However, owing to the low level of exploration, research on the tectono-thermal evolution of Qinnan Depression is still limited. Methods In this study, 25 artificial wells have been established based on 3 seismic profiles of the Qinnan Depression, and their tectonic subsidence and thermal history have been modeled to reconstruct the tectonic-thermal evolution history using a multi-stage finite stretching model. Results The results indicate that since the Cenozoic era, the Qinnan Depression has undergone three stages of rifting and stretching during the sedimentary periods of the Kongdian Formation to fourth member of the Shahejie Formation (65–42 Ma), the third member of the Shahejie Formation (42–38 Ma), and the third member of the Dongying Formation (32.8–30.3 Ma), with a total stretching factor of 1.27–2.05. Corresponding to the three stages of stretching, the basal heat flow of the Qinnan Depression has experienced three stages of increase, reaching a peak of 64.0–89.0 mW/m2 at the end of the deposition of the third member of the Dongying Formation (~30.3 Ma), and then decreased gradually until present. Conclusion The Qinnan Depression underwent three phases of heating and two stages of cooling since the Cenozoic period. There is a good coupling relationship between the tectonic-thermal evolution process and fault activity in the Qinnan Depression. Significance The parameters such as tension system and basement heat flow history obtained in this study are of great significance for understanding the deep dynamic mechanisms of basin tectonic evolution and guiding oil and gas exploration.

Keywords

• bohai basin
• qinnan depression
• structure subsidence
• thermal history
• cainozoic