Evaluation Method for Cement Sheath Sealing Failure Under Sustained Casing Pressure

Abstract

Damage to the cement sheath during well completion, stimulation, and production leads to sealing failure in the well and poses a significant risk to safe operation and the environment. In this paper, based on a predictive model for sustained casing pressure, we propose a method for quantitative evaluation of the extent of cement sheath sealing failure. The composite permeability is selected to characterize the extent of sealing failure. Based on the calculation results for sustained casing pressure, we obtain pressure dependences of the permeability. The composite permeability is calculated based on substituting field data into the proposed model. We analyze and compare the results of the predictive model for the casing pressure in constant annular volume and annular volume expansion scenarios. The results show that the time dependences of the permeability have the shape of an inversely proportional function. The composite permeability of the cement sheath for constant annular volume is 1.90% higher than for the annular volume expansion scenario. With an increase in the time required to establish the sustained pressure (the stabilization time), the permeability decreases and consequently the extent of cement sheath sealing failure decreases. The study results are of practical importance for a quantitative evaluation of the extent of sheath sealing failure for the well and a predictive evaluation of the casing pressure.