Optimisation of hydraulic fracturing parameters based on cohesive zone method in oil shale reservoir with random distribution of weak planes

Hydraulic fracturing technology plays a key role in the in-situ exploitation of oil shale. A mechanism for generating complex fracture networks in oil shale reservoirs with randomly distribution weak planes is of vital importance to hydraulic fracturing design. In this study, the cohesive zone method (CZM) was adopted to establish a reservoir model with randomly distributed weak planes. Furthermore, the concept of "reservoir reconstruction efficiency (RRE)" was proposed as an index to evaluate the results of hydraulic fracturing. Using the proposed model and orthogonal test, we found that the flow rate has the most significant influence on the RRE, followed by the perforation direction and perforation length. For the simulated reservoir, a flow rate of 0.008 m(3)/s and perforation direction consistent with the maximum principal stress were the optimal fracturing parameters. Moreover, numerous radial branch fractures were generated under extremely high flow rate. The findings of this study are expected to provide significant help in predicting the fracture propagation and optimising the fracture parameters in oil shale exploitation.