Controls of strike-slip fault on fractures: Insight from 3D discrete element simulation

The fracture-cave reservoirs controlled by strike-slip faults are the main targets for oil and gas exploration of ultra-deep carbonate in the Tarim Basin. It is of great significance to clarify the distribution rules of fractures related to strike-slip faults for guiding the exploration and development of ultra-deep oil and gas. In this study, six groups of strike-slip fault 3D models based on discrete element numerical simulation method have been created to investigate characteristics of fault-related fracture development and distribution law. In addition, we compared the modeling results to the measurement of fractures from the outcrop of a strike-slip fault in the Northern Tarim Basin to verify their validity. The results show that the stress environment is stable in the simple strike-slip section, and fractures intersecting with the strike-slip direction at a small angle are the principal fracture. In the releasing stepover and double-bend sections, the maximum principal stress changes from horizontal to vertical during the formation of pull-apart zones, where the principal fractures intersect the strike-slip direction at a large angle. The maximum principal stress in the restraining stepover and double-bend section remains horizontal, but their strikes change significantly with the increment of fault displacement. Thus, fractures intersecting the strike-slip direction at a small angle will become principal fractures early on, while those parallel to or anti-intersecting the strike-slip direction at a small angle will become principal fractures later. There are obvious differences in the development of fractures in different structural positions of strike-slip faults. Fractures are mainly concentrated in the fault tips, connections, and fault plane, and the magnitude of the fault damage zone is relatively larger in the first two. Compared with fault displacement, the principal damage zone (PDZ) shows stronger control on the distribution and development intensity of fractures. With the increment of fault displacement, the width of the fault damage zone and the fracture density first rapidly increases before the formation of PDZ and then slows down. Moreover, the formation time of PDZ in the restraining double-bend and stepover section is earlier than the simple strike-slip, releasing double-bend, and releasing stepover sections, and absorb more strain before the formation of the principal displacement zone. Thus, the restraining sections have the highest fracture intensity, followed by the pull-apart sections, then the simple strike-slip section. The results play an important role in understanding the development law of fractures related to strike-slip faults in different arrangements and move modes.