Characterization and Petroleum Geological Significance of the Wrench Structure in the Transtensional Region: A Case from Qikou Sag

The Qikou sag at the central of the Bohai bay basin lies in the superimposition of the extension and strike-slip, and is controlled by the eastern boundary Tanlu fault and the western boundary Taihang Mountain-front strike-slip fault. Through the detailed structural research of the latest large area 3D high precision seismic data, the wrench structures were found as well as the extensional structures in the Paleogene cover of the Qikou sag. On the seismic profiles, the wrench structure can be divided into four types based on the different combination styles of the faults in the basement and the Tertiary cover. They are the slip-complex faulted fold type, slip-simple flower structure type, thrust-simple flower structure type and the slip-deflecting fold type. Meanwhile, the wrench structure not only improved the physical property of the basement rock but also controlled the entrance of the ancient resource and the distribution of the sand. Different reservoirs formed in the pre-Tertiary, Paleogene and Neogene tectospheres. The Paleogene deflecting folds, huge faulted-noses and litho-stratigraphic reservoirs are important exploration fields and the same case with the Neogene reverse drag anticline and the flank of the faulted-noses. The research of the wrench belts is significant for the theory and practice because of the important petroleum exploration success beside the wrench structure belts in last two years.