Abstract:

Small-scale strike-slip faults developed in the Tarim Basin are spatially characterized by "small displacement, long extension, plane segmentation and longitudinal stratification". These geological characteristics, especially the longitudinal stratification, are believed to play an important role in hydrocarbon accumulation. Exploration activities in the Shunbei Oilfield in recent years have come across many fault-karst reservoirs and confirmed the impact of these faults on the pooling of oil and gas. However, how exactly the faults control the process of oil and gas accumulation is not fully clarified. The middle-north section of Shunbei No. 5 fault is selected to carry out a three dimensional assessment of the faults in terms of their role in connecting sources and accumulations as well as controlling, capping and improving reservoirs by using high-precision three-dimensional seismic fault analysis and three-dimensional evaluation technology based on available data of drilling, logging and well performance. The results show that the faults have the characteristics of "vertical layered deformation and plane piecewise evolution" in different structural layers. Their structural responses are also very different, revealing a vertical structural sequence from bottom up of vertical slipping, gypsum-salt detachment structure, flower structure, right-lateral echelon normal fault, left-lateral echelon normal fault and inherited left-lateral echelon normal fault. The structural styles of the faults in different structural layers exert different effect on oil and gas accumulations. This study provides a basis for better understanding the process of oil and gas accumulation and wiser selections of exploration targets, thus can be used as a guiding reference for oil and gas exploration and development in the future.

Key words: fault, oil and gas accumulation system, fault-karst reservoir, strike-slip, Shunbei Oilfield, Tarim Basin