Study on Enhancing Recovery by Multi-Scale Geomechanics Reconstruction and Combined Displacement-Imbibition in Unconventional Resources

In the late stage of development in the X77 Block, reservoir stress depletion has led to rapid productivity decline, requiring an adjustment of the development strategy. A coupled seepage-geomechanics embedded fracture-flow model was established to simulate multi-field interactions, revealing the evolution of pressure, flow, and stress fields after long-term water injection. Results indicate that pressure diffusion is limited, preventing the formation of an effective displacement system, and that changes in minimum horizontal stress exceed those in maximum horizontal stress. A multi-field reconstruction and enhanced oil recovery approach was implemented by re-establishing an artificial fracture-network system through large-scale fracturing, coupled with full-cycle energy supplementation methods-pre-frac energy charging, intra-frac energy boosting, shut-in energy storage, and displacement-drainage integration-to address crossflow and insufficient energy replenishment. Multi-well synergy was used to enhance imbibition and integrate displacement with drainage under a complex fracture network, shifting the strategy from avoiding fractures to utilizing them, thereby improving microscopic sweep and displacement efficiency. Considering gas supply, recovery degree, and economic benefits, four development scenarios were compared, and Scenario 3: CO₂ gravity flooding-was recommended as optimal, involving 3 injectors and 9 producers in S6, and 6 injectors and 33 producers in S7+S8, enabling recovery of 299.6 million tonnes of geological reserves. This provides strong technical support for long-term stable production in the X77 Block.