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

Abstract An embedded fracture flow model integrating seepage and geomechanics was established to conduct multi-field coupled simulations of reservoirs, revealing the evolution patterns of the pressure field, seepage field, and stress field after long-term water injection. Based on these findings, a multi-field reconstruction and combined drive-seepage technology was proposed to enhance oil recovery. The study indicates that after long-term water injection, the pressure diffusion range in the reservoir is limited, making it difficult to establish an effective displacement system. The changes in ground stress exhibit variability, with the horizontal minimum principal stress showing greater variation than the horizontal maximum principal stress. The changes in ground stress around injection wells are more pronounced than those around production wells, with significant stress reorientation near injection wells. The multi-field reconstruction and combined drive-seepage technology reconstructs an artificial volumetric fracture network system by converting injection wells to production wells and employing large-scale fracturing techniques. It effectively addresses the challenges of fluid channeling and energy replenishment after large-scale fracturing through a full-lifecycle energy supplementation approach, including pre-fracturing energy replenishment, in-fracturing energy enhancement, well soaking for energy storage, and combined drive-seepage methods. By leveraging multi-well interactions to strengthen imbibition effects, the technology reconstructs a combined displacement and imbibition system under complex fracture networks, shifting from avoiding fractures to utilizing them, thereby improving microscopic sweep efficiency and oil displacement efficiency. Field application in the GS Block of the Qaidam Basin demonstrated that this technology increased oil recovery by 12 percentage points, enabling cost-effective development at the reservoir scale.