Abstract
The creation of fracture networks via hydraulic fracturing is essential for effective reservoir stimulation, making the interaction between hydraulic and natural fractures a key research focus. As constant-rate injection is still widely adopted in field applications, the majority of existing research is based on this premise. In contrast, the propagation characteristics of hydraulic fractures under variable-rate injection have yet to be fully elucidated. Therefore, this study established a numerical model for hydraulic fracture propagation in naturally fractured reservoirs. The effects of constant-rate, cyclic-rate, and step-rate injection schemes on the interaction between hydraulic and natural fractures was systematically investigated. Furthermore, the influences of the period and amplitude associated with cyclic-rate injection, together with different step-rate injection schemes, on the propagation morphology of hydraulic fractures were analyzed. The results indicate that, compared with constant-rate injection, adopting cyclic-rate or step-rate injection can enhance the interaction patterns between hydraulic fractures and natural fractures. These transforms the originally simple crossing mode into a combined mode involving both crossing and opening. Furthermore, both the period and amplitude of the cyclic injection scheme significantly influence these interaction patterns. However, when the in-situ stress difference exceeds a critical value, the impact of cyclic-rate injection on fracture propagation diminishes, and the in-situ stress becomes the dominant controlling factor. The above findings are of significant importance for guiding field operations and improving fracturing effectiveness.