Research on the dynamic evolution law of four-dimensional in-situ stress during the production process in deep shale gas reservoir.

Deep shale gas is a key area for increasing reserves and production of shale gas in China, and its efficient development is of great strategic significance to national energy security. As the core demonstration area of deep shale gas exploration and development, the complex structure and heterogeneous reservoir conditions in southern Sichuan pose a serious challenge to long-term production safety. The pore pressure drop induced by deep shale gas production drives the dynamic evolution of in-situ stress field through fluid-solid coupling, which is the key geomechanical mechanism to control fracture effectiveness and productivity maintenance. Aiming at the problem of insufficient cognition of this process, based on the seepage-stress coupling theory, a dynamic evolution equation describing the interaction between fluid pressure field and stress field is established, and a seepage-stress coupling in-situ stress dynamic simulation technology system for deep shale gas production process is formed. The results show that the pressure drop diffusion around the well in the early stage of production leads to the sudden increase of effective stress and local stress concentration, which is the main reason for the closure of supporting fractures and the attenuation of conductivity. The high porosity and permeability characteristics of the fracture network make the pore pressure decrease rapidly in the initial stage and then tend to be gentle, and the effective principal stress is significantly negatively correlated with the change of pore pressure. The multi-scale fracture system accelerates the pore pressure attenuation and stress redistribution, and causes the deflection of the in-situ stress direction near the fracture. The simulation of pressure dynamics is in good agreement with the measured results, with a root mean square relative error (RMSRE) of 6.5%, which verifies the accuracy and reliability of the coupling model. The research results deepen the understanding of the dynamic geomechanical evolution mechanism of deep shale reservoirs, provide theoretical support for fracturing optimization design, well pattern deployment and production risk control, and have important scientific and engineering significance for promoting the safe, efficient and sustainable development of deep shale gas.