New Type of Casing Deformation Rising in Weiyuan Changning Shale Gas Play

Abstract

Abstract Casing deformation of shale gas wells reduces the production rate and increases the cost. Early researches showed casing shear deformation due to weak plane slip is the majority in Weiyuan shale gas play. Since 2018, a rising form of casing deformation with elliptical crosssection appeared, defined as casing buckling elliptical deformation in this paper. The mechanism of such deformation is revealed through statistical studies of morphological, geological, and engineering factors. Research indicates that an abrupt change in wellbore trajectory is the critical factor. Elastic deformation is initiated during the casing running process by casing bending and poor cement sheath. The casing is plastically deformed with increased axial load from downhole tools trapping during the downhole operation and/or hydraulic fracturing induced cracking. Downhole tools are free to pass through with casing diameter remains in elastic stage, whereas tools encounter difficulties to pass through when the diameter is narrowed in plastic deformation. Casing buckling elliptical deformation can be easily identified by the elliptical shape in crosssections and centrosymmetric extrusion and intrusion in 3D views generated from the result of MFC logs. A clear understanding of the mechanism is necessary for further study on effective countermeasures for casing buckling deformation in shale gas wells.