Evaluation of the controlling effect of new annulus materials on casing deformation in shale gas wells

Abstract

Shale gas horizontal wells have severe problems of casing deformation and failure due to formation displacement during fracturing. Statistics show that casing deformation problems occur frequently in the development of shale gas, especially in Sichuan Basin. Furthermore, the phenomenon of formation extrusion and fault slip is serious, which has caused great obstacles to the development of shale gas in China. In view of the current lack of casing deformation control methods, a finite element model of a wellbore under formation displacement load is established in this paper. The stress and deformation of the casing are simulated, and the mitigating effects of new annular materials such as a modified cement sheath and rubber are evaluated. Results indicate that the formation extrusion and fault slip can cause radial oval deformation and axial S-shaped deformation of the production casing, respectively. The use of a modified cement sheath can provide a little mitigating effect on casing deformation. Meanwhile, using rubber cementing can play a strong protective role for the production casing and avoid casing deformation to a certain extent. This research can provide a new way and important reference for the prevention and control of casing deformation in shale gas wells.