A hybrid dual-medium discrete fracture model for horizontal wells with complex fracture systems and waterflooding interference

Pressure transport in tight reservoirs is controlled by rapid flow through conductive fractures, delayed exchange between the matrix and fractures, and the interaction of pressure disturbances caused by injection and production. These coupled processes remain insufficiently understood. This study develops a hybrid model that combines a dual-medium representation with explicit fractures for oil–water flow in multistage fractured horizontal wells under waterflooding. Hydraulic fractures and major natural fractures are represented explicitly, whereas the stimulated reservoir volume is described as a dual-medium system. A shape factor derived from pressure diffusion tests on irregular matrix blocks is introduced to characterize matrix–fracture exchange, and a pressure support coefficient is defined to quantify injection support. The formulation reproduces the Lim–Aziz solution for a cubic block with a relative difference of 2.54%, and the implementation is verified against KAPPA. The pressure response exhibits eight flow regimes. The late time downward departure of the pressure and pressure derivative curves results from the overlap of pressurization caused by injection and depletion caused by production. A continuous fracture pathway between the injector and producer accelerates pressure communication and water migration, producing the strongest pressure support but the greatest risk of water breakthrough among the tested cases. Increasing the injection rate strengthens and advances the interference response, whereas reducing well spacing shortens its arrival time. A field case demonstrates the applicability of the model to pressure transient matching and fracture parameter interpretation.