Study on Reducing Casing Shear Deformation by Using Composite Cement Slurry Column Structure

Abstract

ABSTRACT Shale reservoirs are usually developed by horizontal wells and staged fracturing, and severe casing deformation occurs during development. The main deformation form is shear deformation. The main reason for casing shear deformation is that during hydraulic fracturing, when the fracturing fluid enters the natural fracture or weak cementation surface, the normal stress between the fracture surface or bedding surface will be significantly reduced, and the friction coefficient between the two will also be substantially reduced, which will lead to relative sliding of the rock mass on both sides of the fracture or bedding. Once the rock mass slips, it will lead to shear deformation of the casing. Given this, a method of reducing casing shear deformation using composite cement slurry column structure is proposed: inject conventional cement slurry, elastic and ductile cement slurry, and cement slurry containing hollow glass beads into the wellbore in sections. The high porosity cement sheath formed by cement slurry containing hollow glass beads can effectively reduce the degree of casing shear deformation during formation slip, and the elastic and ductile cement slurry can effectively seal the possible gas channeling problem. During the research, the optimal rheological model of the composite cement slurry column was optimized, the change of the annulus pressure loss caused by the mixing was calculated, and the influence of the cement sheath formed by the structure solidification of the composite cement slurry column on the reduction of the shear deformation of the casing was analyzed. The research results show that the established rheological composite cement slurry column model can be well applied to the project site. Still, the influence of the cement slurry system on friction should be considered in the use process. The cement sheath formed by cement slurry containing hollow glass beads can effectively reduce the shear deformation of the casing. With the continuous increase of the content of hollow glass beads, the ability to reduce the shear deformation of the casing is continuously improved. The research results provide a new way to solve the problem of casing deformation caused by interlayer slip and shear during hydraulic fracturing.