Study on Main Controlling Factors of Natural Fracture Development in Shale Reservoir

天然裂缝作为页岩储层的重要储集以及渗流通道，文章以四川盆地南部渝西地区五峰组–龙马溪组页岩为例，基于岩心观察与成像测井等手段，开展天然裂缝类型、分布特征以及主控因素的研究。研究结果表明本地区五峰–龙马溪组天然裂缝密度自下至上呈现逐渐减小的特征，天然裂缝类型主要包括层理缝、高导缝、高阻缝。其中层理缝最为发育。裂缝倾角的最大范围主要集中于0˚~10˚。裂缝发育受断裂发育带控制明显，南部较北部裂缝发育程度明显偏高，天然裂缝发育主控因素分析表明，渝西地区天然裂缝发育程度主要受构造作用与沉积作用控制，距离断裂越近，天然裂缝发育密度越大；脆性矿物含量越高，天然裂缝密度越大，黏土矿物含量越高，天然裂缝密度越小。文章研究结果可以为深入了解海相页岩储层天然裂缝主控因素提供有力支撑。Natural fractures are important reservoirs and seepage channels of shale reservoirs. In this paper, taking the shale of Wufeng Formation and Longmaxi Formation in West Chongqing area of southern Sichuan Basin as an example, the types, distribution characteristics and main controlling factors of natural fractures are studied based on core observation and imaging logging methods. The results show that the density of natural fractures in Wufeng-Longmaxi Formation decreases gradually from bottom to top, and the types of natural fractures mainly include bedding fractures, high conductivity fractures and high resistance fractures. Among them, the bedding seam is the most developed. The maximum range of fracture inclination is mainly concentrated in 0˚~10˚. The fracture development is obviously controlled by the fault development zone, and the fracture development degree in the south is obviously higher than that in the north. The analysis of the main controlling factors of natural fracture development shows that the natural fracture development degree in the west Chongqing area is mainly controlled by tectonic and sedimentary processes. The higher the brittle mineral content, the higher the natural fracture density, the higher the clay mineral content, the smaller the natural fracture density. The results of this study can provide favorable support for further understanding of the main controlling factors of natural fractures in Marine shale reservoirs.