Abstract: The casing deformation in shale gas wells in Weirong area is a prominent problem, but the mechanism that causes casing deformation in this area is still unclear. In this paper, based on the physical and chemical properties of shale, the effect of shale expansion strain on casing stress was analyzed, and the relationship between cementing quality and casing deformation under the consideration of shale expansion strain was studied. It was found in the study that the shale in the Weirong area was hard and brittle, with high mechanical strength and insignificant strength changes after hydration and the combined action of shale expansion strain and cementing quality exerted a significant effect on the casing stress. When cement sheath was missing and micro-annulus existed, there was sufficient space for releasing expansion strain to reduce casing stress. When the expansion stress could not be released completely, it was necessary to ensure the structural integrity of wellbore assembly. High-density perforation had a positive effect on the release of expansion strain. High-density perforation based on reasonable perforation parameters was one of the effective measures to prevent casing deformation. This study provides a reference for the study of casing deformation mechanism in similar shale gas reservoir.

Key words: shale gas reservoir, shale expansion, casing deformation, cementing quality, stress release, high-density perforation