CDEM-Based Simulation of Fracture Propagation Characteristics during Variable-Rate Hydraulic Fracturing in Tight Reservoirs

Abstract The construction of complex fracture networks is essential for enlarging the stimulated reservoir volume (SRV) and enhancing hydrocarbon production in tight reservoirs. Variable-rate hydraulic fracturing induces periodic stress perturbations by modulating the injection rate, thereby redistributing the local stress field and facilitating the formation of secondary and branched fractures. To elucidate this mechanism, a numerical model of variable-rate fracturing based on the Continuum–Discontinuum Element Method (CDEM) was developed to simulate fracture initiation and propagation under various injection scenarios. The effects of cyclic rate amplitude, cycle duration, and horizontal stress difference on fracture evolution were systematically investigated. The simulation results indicate that, compared with constant-rate and stepwise-rate injection, cyclic fracturing significantly enhances the complexity of fracture networks in tight reservoirs. Increasing the rate amplitude and shortening the cycle duration promote fracture branching and development, thereby expanding the stimulated region. Conversely, an increase in horizontal stress difference reduces the effectiveness of cyclic injection and diminishes the resulting fracture network complexity. These findings provide theoretical insights for optimizing variable-rate fracturing parameters, enhancing the formation of complex fracture networks, and guiding hydraulic fracturing design under varying stress-field conditions.