Integrity assessment methodology of casing ovality deformation in shale gas wells

Abstract

Casing deformation frequently occurs in shale gas wells during hydraulic fracturing. While the failure mechanism of casing ovality deformation is unclear due to the interweaving and compounding reasons from geological and engineering complexity. The multi-arm caliper tool can quantify the severity of casing deformation, and the spatial and temporal occurrence of casing deformations is analyzed. A finite element model of fractured shale squeezing casing is established to simulate the process of casing deformation. The simulated casing deformation is compared with logging data to validate the model with which the deformation mechanism would be revealed. Simulation results indicate that casing deformation in the Luzhou shale gas field belongs to compressive deformation. The length of casing deformation and the diameter shrinkage are local and small, and the deformation points are scattered along the horizontal well trajectory. The fracturing fluid pressure and fractured shale block generate a nonuniform load on the casing, which leads to stress yield and ovality deformation. The fluid pressure, formation degradation and cementing material are the key controlling factors to mitigate casing ovality deformation. This work provides a prompt & accurate assessment method and controlling measures for casing integrity in shale gas wells.