Reservoir controlling differences between consequent faults and antithetic faults in slope area outside of source: A case study of the south-central Wenan slope of Jizhong Depression, Bohai Bay Basin, East China

Abstract The control effects of different occurrence faults on oil and gas accumulation and distribution in the outer slope area of oil and gas reservoirs were studied taking the south-central Wen'an slope of the Jizhong depression in the Bohai Bay Basin as an example. Based on 3D seismic data and the distribution of oil and water, the controlling differences between consequent fault and antithetic fault were analyzed and compared from the formation and evolution rule of faults and the formation mechanism of fault traps, including development positions of the consequent fault traps and antithetic fault traps, oil and gas distribution horizon adjusted by fault and formation period of fault traps. The differences between consequent faults and antithetic faults in controlling reservoirs have three main aspects: (1) Consequent fault traps and antithetic fault traps are in different positions, the consequent fault traps are at the segmented growing point in the hanging wall of “hard-linkage” faults, while the antithetic fault traps are developed in the position with the largest throw in the footwall because of tilting action; (2) The two kinds of faults result in different oil and gas distribution vertically, oil and gas adjusted by consequent faults is distributed in a single layer or multi-layers, while oil and gas adjusted by antithetic faults occur in single layers; (3) The two kinds of fault traps are formed in different periods, the consequent fault traps are formed at the time when the related faults enter the stage of “hard-linkage”, while the antithetic fault traps are formed at the beginning of the fault active period.