Modeling of nonlinear properties of casing centralizers equipped with axial thrust

Abstract

The issue of qualitative centering of the casing in wells with complex trajectory is considered. When choosing an effective centralizer, two competing requirements are simultaneously assigned to its mechanical properties. The centralizer must have sufficiently low stiffness in order to provide the descent of the casing into wellbore. At the same time, the centralizer must have high stiffness in order to provide proper clearance gap for high-quality cementing of the annular space. Several new designs of rod centralizers are proposed in the paper. Their main feature is that they are equipped with an additional thrust ring, which allows one to change the mechanical characteristics of the centralizer at high contact loadings. The boundary-value problems for the differential equations of mechanics of the arc rods with boundary conditions in the form of inequalities are formulated and solved. Analytical relations between the clamping force and mutual approach of the casing and the well wall, which characterize the radial stiffness of the centralizer equipped with axial thrust, are determined. It is established that the described designs of the centralizers have essentially nonlinear characteristics that contribute to the efficient centering of the casing. At vertical and slightly deviated from the vertical intervals of the wellbore, the centralizer behaves as soft and does not interfere with the descent of the string; at intervals with large curvature of the wellbore the stiffness of the centralizer increases due to the axial thrusts.