Study and Application of Cement Slurry for Mitigating Casing Deformation in Shale Gas Well Fracturing

Shale gas reservoirs in the Sichuan-Chongqing area have complex geological structures and well-developed natural fractures, which always result in formation slip and casing deformation in long horizontal section well tight cluster fracturing operation. A new cement slurry system was developed to mitigate casing deformation problem and its performance was verified in field test. Based on the integrated finite element simulation of geology-engineering, the effect of the elastic modulus and deformation capacity of set cement on the casing stress were systematically analyzed, and it was determined to decrease the elastic modulus and to improve the deformation capacity of the set cement. A cement slurry was then developed using highly deformable materials and elastic materials, it has a moderate elastic modulus (< 5 GPa), the set cement has a deformation rate of more than 25%, and its engineering performance satisfies the needs of field operations. This cement slurry was successfully used on the well Z-1. Laboratory shear test results showed that this cement slurry can mitigate casing deformation better than other conventional cement slurries. In field fracturing operation, no casing deformation occurred during the whole operation process, confirming the remarkable technical effect of this cement slurry. The development of this cement slurry provides an innovative solution to the management of wellbore integrity in the whole lifecycle of shale gas wells.