Numerical Modeling of Casing-Cement Failure in Geothermal Wells Using Modified CZM Bonding Conditions

Abstract

Experimental testing of casing cement debonding has shown that a remaining axial force similar to friction is noticed after shear debonding. This cannot be explained using pure CZM models since no normal force exists after debonding; thus, the friction force should have been zero. A modified boundary condition scenario has been created to understand this phenomenon better. A CZM model is used until the debonding is created, after which the stress conditions are transferred to a friction bonding model between cement and pipe. The results have shown that the remaining friction force can be significant and may justify limited wellhead growth in geothermal wells due to thermal expansion. The paper will show the numerical model and the simulation results modeled around a synthetic geothermal well. The results will help well-design engineers improve short—and long-term well integrity and better well-head prediction.