Multi-mode flow simulation of fracture-cavity reservoirs and predicting oil accumulation based on hydro-mechanical-damage coupling model

Abstract

Fracture-cavity carbonate reservoirs exhibit significant heterogeneity with diverse flow modes, including porous media seepage and free flow, within fractures and cavities. This complexity is further compounded by tectonic stress. Traditional oil reservoir seepage theories often struggle to depict these fluid flow characteristics accurately. This study employs a hydraulic-mechanical-damage coupling model to conduct numerical simulations of multi-mode fluid flow within fracture-cavity reservoirs. This approach elucidates fluid flow mechanisms influenced by multi-field coupling and predicts areas favorable for oil accumulation based on actual geological models. The results show that (1) while the secondary fractures developed in the penetrating-type fracture-cavity body result in the highest oil migration efficiency and initial production, the production from this body type decreases rapidly in the later stage. Secondary fractures in the sandwich-type and side-type cavity bodies primarily offer storage, resulting in lower initial production but a slower production decline. (2) In the S1 stress state, secondary fractures primarily connect fracture-cavity bodies, whereas, in the S2 stress state, they mainly contribute to oil accumulation. (3) Secondary fractures function as efficient conduits for oil migration, and their distribution is influenced by the presence of fault zones and cavities. Consequently, the intersection of cavities and fault zones with secondary fractures leads to the formation of favorable oil accumulation areas.