Optimisation of Perforation Parameters for Enhanced Fracture Network Complexity in Oil Shale Reservoirs: Integrating Cohesive Zone Method with Response Surface Methodology

• The cumulative fracture length and maximum fracture width serve as evaluation values for hydraulic fracturing effectiveness. • The cumulative fracture length and maximum fracture width exhibit a positive correlation with the fracturing fluid discharge rate, though a critical threshold exists. • The cumulative fracture length was primarily controlled by perforation length, and the maximum fracture width was dominated by the perforation phase. • Optimising fracture morphology hinges on understanding and leveraging these synergistic mechanisms between flow rate and other parameters, rather than isolating individual variables. Perforation hydraulic fracturing plays a key role in the in-situ exploitation of oil shale. This study aims to clarify the quantitative influence patterns of fracturing fluid flow rate, perforation phase, and perforation length on cumulative fracture length and maximum fracture width. Single-factor analysis reveals that cumulative fracture length and maximum fracture width exhibit a positive correlation with fracturing fluid flow rate. However, a critical threshold exists (flow rate: 0.07 m³/s, perforation phase: 120°, perforation length: 0.3m). Beyond this threshold, further increases in parameters actually inhibit the propagation of fractures. Using ANOVA and response surface methodology, quadratic regression models were developed for cumulative fracture length and maximum fracture width as functions of fracturing parameters. Results revealed significant differences and nonlinear characteristics in the influences of parameters: cumulative fracture length was primarily controlled by perforation length (highly substantial effect). In contrast, maximum fracture width was dominated by the perforation phase (highly considerable effect). While the flow rate of fracturing fluid had a relatively minor impact on cumulative fracture length and maximum fracture width, distinct optimisation ranges were identified. The study also revealed interactions among hydraulic fracturing parameters, with the flow rate exhibiting a significant synergistic impact with both the perforation phase and perforation length. Optimising fracture morphology hinges on understanding and leveraging these synergistic mechanisms between flow rate and other parameters, rather than isolating individual variables. Ultimately, multi-objective optimisation identified the optimal perforated fracturing parameter combination: a fracturing fluid flow rate of 0.07 m³/s, a perforation phase of 140°, and a perforation length of 0.3 m. Under these parameters, a cumulative fracture length of 120.28 m and a maximum fracture width of 10 mm were achieved. This study reveals the primary factors controlling fracture propagation in oil shale fracturing. The proposed optimised parameter combination provides direct and reliable theoretical support for achieving efficient fracture network modification in field operations.