Coupled seepage-mechanical modeling to evaluate formation deformation and casing failure in waterflooding oilfields

Waterflooding implemented to enhance oil recovery could concomitantly induce formation deformation and casing failure. The adverse responses should be evaluated to ensure the safety and performance of wells. A coupled seepage-mechanical model is developed to analyze the responses of formation and wells in waterflooding oilfields. The fluid-solid coupling method is employed to capture the flow and deformation in interlayers. The behavior of casing is predicted from the mechanical interaction among the wellbore-cement sheathcasing system. This model is validated by the analytical result. Results indicate that injection-production unbalance causes nonuniform pressurization or depletion in formation. Under pressurization, the vertical displacement along wellbore increases with the increases of axial position and time and displays a sharp rise in mudstone layer. There is an offset in mudstone layer. Casing stress increases under continuous pressurization or depletion, and stress concentration occurs in the mudstone interval. The predicted casing yield situation is consistent with the failure location in oilfield. The incongruous displacement in mudstone is the mechanism of casing deformation. Sustaining injection-production balance and adopting no-cementation operation are the possible strategies for mitigating the adverse effects of waterflooding. The findings can be applied to evaluate and manage formation response and casing integrity in waterflooding oilfields.