The Structure And Structural Evolution Of The Fourth Member Of The Shahejie Formation And Kongdian Formation In Huimin Depression

The fourth member of the Shahejie Formation and Kongdian Formation become the key strata of oil and gas exploration in Huimin depression. Guided by many theories and technologies, such as structuralgeology, new plate tectonics, high-resolution sequence stratigraphy, comprehensive research is applied to the structure and structural evolution of the fourth member of the Shahejie Formation and Kongdian Formation combining drilling with sequence analysis, regional background of structures with analysis of faults.The stratigraphic frame of the deep strata is confirmed by comprehensive analyses, which are based on seismic profiles and are combined with the stratigraphic sequence of wells. Comparing with different methods which are used to study the activities of faults, the main faults of Huimin depression are analyzed by fault throw method and fault growing rate method. Some typical profiles such as 463, 483, 523 and 542 seismic profiles are back stripped to compile balanced sections. The characteristic of structural evolution of Huimin depression are concluded combining with the analysis of the structural evolution of four balanced sections.The following conclusions can be summarized: (1) The deep strata is divided into two groups: Kongdian Formation (T7-TR) and he fourth member of the Shahejie Formation (T6-T7). The geological meanings of T6, T7, T8 and TR are unified. (2) Fault throw method and fault growing rate method are suitable for the study of the activities of the faults in Huimin depression. (3) The NE and NEE trending are the primary directions of the main faults, excepting for Linbei fault which is NWW trending. The main active periods of faults are from Ek to Es2. The activity of Zizhen fault, Yangxin fault and Qihe fault are from strong to weak. Xiakou fault have an active peak value in Ek and Es2-Es3, while the other faults are most active in Es4 and Es2-Es3. (4) The structural evolution in Huimin Depression can be divided into the following four phases: the uplifting and setting phase in Paleozoic, the rifting phase in Mesozoic, the faulting phase in Paleogene and the depressing phase in Neogene. The rudiment of sag controlled faults are succeed to develope in the early period of Ek. Then, with the great effect of the extensional stress field in the following periods of Ek, the whole Huimin depression extended in the NE direction, and slipped dextrally, while the reversal faults tuned into normal. The strata of north region tilt dextrally in the Es4 period. The sedimentary center was located at the downthrown of growth faults, and moving to the north gradually.