Coupling mechanisms between natural fractures and casing deformation in shale reservoirs: a review

Casing deformation frequently occurs during hydraulic fracturing operations in deep shale reservoirs. In severe cases, it impedes the deployment of downhole tools, compromising the production efficiency of oil and gas wells. The primary cause of casing deformation is the shear slip of pre-existing natural fractures, which is differentially regulated by multiple factors as previous studies suggest: stress disturbance is the dominant factor, directly governing the redistribution of in-situ stresses; fluid-rock interactions and cementation strength are critical in controlling the instability of fracture zones, with fluid infiltration and cement dissolution significantly weakening the frictional stability of fracture surfaces; the risk of shear rupture increases substantially when the fracture angle ranges between 30° and 45° according to shear failure criteria; how thermo-hydro-mechanical (THM) coupling effects affect fracture instability still invites further understanding. This review also summarizes current research methodologies for investigating casing deformation: field investigations, numerical simulations, and true triaxial physical experiments, along with their respective limitations. Future directions are outlined on the mechanisms of natural fractures on casing deformation, providing references for the prevention and control of casing deformation.