Mechanisms of Casing Deformation during Hydraulic Fracturing in the Horizontal Wells of the Weirong Shale Field

Casing deformation is frequent during hydraulic fracturing in the Weirong shale gas field, which impedes shale gas production. We investigated the effect of shale elastic modulus on casing deformation based on shale swelling in this work. According to field data, the silicon content in the Weirong shale gas field has a considerable impact on casing deformation during hydraulic fracturing. Furthermore, the results of the experiment show that the silicon content is positively related to the elastic modulus of shale. We conducted numerical simulations to analyze the casing deformation based on shale swelling. We observed that the shale elastic modulus was negatively correlated with the casing stress without shale swelling; however, the shale elastic modulus was positively correlated to casing stress with shale swelling. Furthermore, when the elastic modulus remained constant, casing stress was positively correlated with shale swelling. The numerical simulation results were validated using field data from the WY23-5 shale well. Moreover, factors such as injection pressure, formation pressure, and cement sheath elastic modulus can increase the impact of the shale elastic modulus on casing deformation with shale swelling. Casing deformation is greatly influenced by the distribution of the stimulated reservoir volume (SRV) area. Different SRV area behaviors result in different types of casing deformation. The symmetric distribution of the SRV area causes casing extrusion deformation, whereas the asymmetric distribution of the SRV area causes casing bending deformation. Moreover, casing stress is positively correlated with the length of the SRV area.