The failure law of the cement plug-casing interface for direct plugging in the casing of old wells for salt cavern gas storage

Abstract

The old salt hole wells cannot be directly converted into gas storage, injection and production wells, so the old wells must be plugged to ensure the effectiveness of plugging. Aiming at the plugging problem of old wells in salt cavern gas storage, a finite element model of the formation-cement sheath-casing-cement plug assembly suitable for direct plugging in the casing of salt cavern gas storage is established to simulate the fracture stripping process of the cement plug-casing interface. The results show that under the pressure of the gas storage, the cement plug casing bonding interface will undergo shear deformation, and after stacking to a certain extent, peeling phenomenon will occur. As the simulation time increases, the peel failure length gradually increases and tends to stabilize, reaching the limit of peel failure length. In the process of research, the factors and laws affecting the peeling failure length are also analyzed. It is found that the peeling failure length of the cement-casing interface is related to the maximum operating pressure of the gas storage, the length of the cement plug, the diameter of the cement plug, the elastic modulus, Poisson’s ratio. The research results are helpful to judge whether the plugging length in the casing is sufficient, and provide theoretical guidance to ensure the long-term safe operation of the gas storage.