Role of natural fractures with topology structure for hydraulic fracture propagation in continental shale reservoir

Natural fractures tend to further promote fracture network which is initiated by hydraulic frac-turing. However, how natural fractures with various topology structures impact hydraulic frac-ture propagation in continental shale reservoir is still unclear. With Fullbore Microscan Imager (FMI) and geo-statistics of Chang 7 reservoir in Yanchang Formation, typical natural fractures are classified into three topology structures, which are natural fractures with type I, type II and type III nodes respectively, and the average occurrence strikes of natural fractures with type I, type II and type III nodes are SW260 degrees, SW255 degrees and SW255 degrees. Coupling with seepage field and stress field, a model simulating fracture initiation and propagation is established considering the transversely isotropic property of continental shale reservoir. On this basis, the role of typical natural fractures with topology structure for hydraulic fracture propagation is studied qualitatively and quanti-tatively by Finite Element Method (FEM) with globally embedded cohesive element. Natural fractures with type II nodes have largest effect on inducing hydraulic fracture propagation, hy-draulic fractures can communicate most easily with them, and also the length and velocity of hydraulic fracture propagation are the longest and fastest, so fracture network is the most com-plex after fracturing in naturally fractured continental shale reservoir with type II nodes, which follows by the effect of hydraulic fracture propagation in naturally fractured continental shale reservoir with type III nodes. In comparison, natural fractures with type I nodes have insignificant impacts on hydraulic fracture propagation. The research results are conductive to fracturing design in continental shale reservoir.

Automated summary

This study classified typical natural fractures in the Chang 7 reservoir of the Yanchang Formation using Fullbore Microscan Imager (FMI) and geostatistics. The results showed that natural fractures with different topology structures have different impacts on hydraulic fracture propagation. Among them, natural fractures with type II nodes have the largest effect, with the longest and fastest propagation velocity, leading to the most complex fracture network.