Geological characteristics and models of fault-fold-fracture body in deep tight sandstone of the second member of Upper Triassic Xujiahe Formation in Xinchang structural belt of Sichuan Basin, SW China

Abstract

In the second member of the Upper Triassic Xujiahe Formation (T3x2) in the Xinchang area, western Sichuan Basin, only a low percent of reserves has been recovered, and the geological model of gas reservoir sweet spot remains unclear. Based on a large number of core, field outcrop, test and logging-seismic data, the T3x2 gas reservoir in the Xinchang area is examined. The concept of fault-fold-fracture body (FFFB) is proposed, and its types are recognized. The main factors controlling fracture development are identified, and the geological models of FFFB are established. FFFB refers to faults, folds and associated fractures reservoirs. According to the characteristics and genesis, FFFBs can be divided into three types: fault-fracture body, fold-fracture body, and fault-fold body. In the hanging wall of the fault, the closer to the fault, the more developed the effective fractures; the greater the fold amplitude and the closer to the fold hinge plane, the more developed the effective fractures. Two types of geological models of FFFB are established: fault-fold fracture, and matrix storage and permeability. The former can be divided into two subtypes: network fracture, and single structural fracture, and the later can be divided into three subtypes: bedding fracture, low permeability pore, and extremely low permeability pore. The process for evaluating favorable FFFB zones was formed to define favorable development targets and support the well deployment for purpose of high production. The study results provide a reference for the exploration and development of deep tight sandstone oil and gas reservoirs in China.