Study on oil–water two-phase flow characteristics and influencing factors in fractured-cavity reservoirs considering hydraulic-mechanical coupling

Fractured-cavity reservoirs are highly inhomogeneous with coexisting matrix, fractures, and cavities, making it extremely difficult to characterize fluid flow, and posing a significant challenge to efficient development. In this study, the hydraulic-mechanical coupling model of oil–water seepage-free flow for fractured-cavity reservoirs was constructed, and the correctness was verified by physical model experiments. Then, through numerical simulation, the influences of cavity parameters (quantity, size, and distribution) and fracture-cavity combination patterns were analyzed, revealing the controlling mechanisms of fracture-cavity patterns on oil–water flow characteristics. The results showed that with increasing quantity and diameter of cavities, the shielding effect and dominant role became increasingly pronounced, leading to reduced reservoir connectivity and difficulty in forming significant dominant flow channels. The cavities and fractures along the direction connecting injection and production wells formed favorable dominant flow channels with superior connectivity. Remote cavity distributions from production wells could accelerate water breakthrough time, while proximal cavity clusters near production wells tended to form localized isolation zones with lower displacement efficiency and reduced water cut. The connectivity of fracture-cavity combination models followed this descending order: Series–parallel type > parallel type > series type. Furthermore, the water cut levels of the three models showed consistent ranking with their connectivity patterns. The results provide theoretical support for the evaluation of oil–water distribution and the optimization design of development plans in fractured-cavity reservoirs.