A study on the reservoir controlling characteristics and mechanism of the strike slip faults in the northern slope of Tazhong uplift, Tarim Basin, China

Abstract

There are many strike-slip faults in Ordovician carbonate reservoirs on the northern slope of Tazhong uplift and its adjacent areas in Tarim Basin, China. These faults play an essential role in the reservoirs controlling in this area, but the internal structural characteristics of the strike-slip faults are still unclear. Based on core observation, imaging logging, 3D seismic data, and well test data, the reservoir space and internal structure of the S-1, S-7, and S-5M fault zones are studied using structural kinematics, geometry, and dynamics methods. Based on the detailed description of the internal structural characteristics of the specific geometric segments of S-1 and S-5M fault zones, the reservoir-controlling characteristics and accumulation mechanism of strike-slip fault zones in Ordovician carbonate strata are analyzed. It is found that S-1, S-7, and S-5M fault zones have the characteristics of segmented deformation and can be divided into several independent geometric segments. Above the T74 interface (the top of Yijianfang Formation of Middle Ordovician), the S-1 fault zone can be divided into 8 geometric segments, the S-7 fault zone into 2 geometric segments, and the S-5M fault zone into 6 geometric segments. Each geometric segment is a set of an independent reservoir. Each geometric segment comprises fractures and caves, which have the structural characteristics of a “fracture-cavity unit.” According to the statistics, the geometric segments with a length of 6–7km and multiple sets of “fracture-cavity unit” composite structure have adequate fluid enrichment, more likely to be the reservoir sweet spots. The research results have important guiding significance for exploring and developing the middle-lower Ordovician strike-slip fault reservoirs in Tarim Basin.