Evolution mechanism and hydrocarbon reservoir characteristics of typical slope zones in Jizhong Depression, Bohai Bay Basin

The width and gradient of slope zones in faulted basins in China were studied. The tectonic evolution mechanism and hydrocarbon reservoir characteristics of various types of slope zones were discussed from the aspects of structural geometry and kinematics based on the seismic and geological data collected mainly from the Wen'an, Lixian and Shulu West slopes in the Jizhong Depression. According to slope gradient and width, three types of slope zones were classified:wide-gentle type, platform type and narrow-steep type, corresponding to the Wen'an, Lixian and Shulu West slopes, respectively. The wide-gentle type slope was characterized by a single-break and shallow detachment, and was dominated by sedimentation. Oil and gas migrated horizontally for a long distance and was enriched in multiple layers with various trap types. The platform type slope was characterized by double-breaks and medium detachment, and was controlled by both structure and sedimentation. The hydrocarbon abundance in the platform type slope depended on the hydrocarbon-producing subsags in slopes, and the traps were mainly nose-like or lithologic pinch-out types. The narrow-steep slope was characterized by a single-break and deep detachment, and was dominated by structure. Oil and gas migrated vertically and was mainly enriched in structural traps.