Borehole stability study of water injection wells in fluid-solid coupling

During the production process of water injection oilfield, in-situ stress field is influenced by seepage field, leading tostress concentration near the borehole. This paper studies the mechanical mechanism of casing damage in fluid-solid coupling duringwater injection. Based on conventional Biot equation, considering the medium permeability change with ground stress, the paperdevelops a nonlinear coupling mathematical model for fluid seepage and solid elastic-plastic deformation during injection-productionprocess. The model is solved with full-coupled finite element method. In addition, through numerical simulation for injecting processof a water injection well in Nan’er zone of Daqing Oilfield, the paper analyzes the effect of water injection on pore pressure, the stressfield and deformation field of the rock around the borehole. Relationship of reservoir pore pressure and borehole stress with time isalso contrasted under different injection-production conditions. Simulation results show that fluid-solid coupling in water injectionreservoirs has great influence on stress field and deformation field of borehole rock. The results are very helpful to develop fluidsolidcoupling mathematical model during water injection development, control optimum injection-production pressure difference andprevent or mitigate the casing damage in oil field.