Assessment on the cement integrity of CO2 injection wells through a wellbore flow model and stress analysis

Abstract

This work aims at assessing the cement integrity during CO2 injection by illustrating the relevance of injection operations to the failure modes of cement. A single-phase flow model for pure CO2 is developed to provide the temperature and pressure profiles in the well and solved by a finite difference method. With the downhole temperature predicted by the flow model as a boundary condition, we present a mechanical model to estimate the stress state in the well section under plane-strain conditions as well as the stress intensity factor at a radial crack tip. This study introduces four failure factors corresponding to shear compressive failure, radial cracking, interfacial debonding, and fracture propagation. Further parametric studies are implemented to reveal the effects of injection operations, including injection temperature, rate, and time, on the above failure factors. They indicate that the injection rate is the most influential factor for cement integrity. High injection rates could cause radial cracking and its propagation as well as interfacial debonding but reduce the risk of shear compressive failure. Low injection temperatures or a long injection time would undermine the tensile and interfacial strength and extend the radial crack in cement while they benefit on shear compressive strength. The results provide guidelines to optimize injection operations for long-term well integrity during CO2 injection.