Natural fractures development characteristics and effectiveness restrict petroleum exploration and development of tight sandstone gas reservoirs. Taking Xujiahe Formation in Yuanba area of Sichuan Basin as an example, based on the field outcrop, core, thin slice, imaging logging, experimental analysis and production dynamics data, the characteristics and effectiveness of natural fractures are studied. Natural fractures of Xujiahe Formation are relatively well developed in Yuanba area, and structural shear fractures are the most developed ones, the fracture effectiveness is better. According to the dip angle, the fractures are mainly composed of high angle fractures that almost vertical to the strata, the main strike of the fractures is NW-SE, nearly E-W, nearly S-N and NE-SW. The formation period of natural fractures can be divided into four stages：Diagenetic period; the middle-late Yanshan tectonic movement; the early-middle Himalaya tectonic movement; the late Himalaya tectonic movement. The control factors of the fracture effectiveness are the filling and opening degree, fracture formation period and the maximum horizontal principal stress. There are obvious differences in the effectiveness of different types and different strike of the fractures, the effectiveness of high angle fractures, vertical fractures and NW-SE, nearly E-W fractures is the best, which is of great significance for the development of tight sandstone gas reservoirs.
Li Hu Tang Hongming Qin Qirong Hu Dongfeng Qin Zhangjin Zhou Jiling5. Development characteristics and effectiveness evaluation of natural fractures in tight gas sandstones：A case study in Xujiahe Formation of Yuanba area, Sichuan Basin[J]. Chinese Journal of Geology, 2019, 54(2): 356-372.