Damage modeling of CO₂ injection well interfaces under coupled thermal, hydraulic and mechanical behavior

Abstract

This paper presents an investigation of well integrity during low-temperature CO₂ injection using a model of thermo-poroelasticity with interface damage mechanics. The casing–cement and cement–formation interfaces are described using cohesive interface elements and a bilinear traction–separation law. Verification testing is performed to establish the correct implementation of the coupled thermal, hydraulic, and mechanical equations. Simulation scenarios are developed to determine well interface damage initiation and development for intact wells and wells with an initial defect in the form of a 45° debonded azimuth. Each intact and defective well was simulated for 30 days of CO₂ injection at selected temperatures. Under the conditions considered, tensile radial stress developed at both the casing–cement and cement–formation interfaces. Hoop stress in the cement sheath remained compressive after 30 days but with reduced magnitude at the lower injection temperature, indicating greater risk of tensile stress and radial cracking as the injection temperature was reduced. Damage occurred in two of four scenarios considered, namely, the intact and defective wells at an injection temperature of 10° 𝐂, and was limited to the casing–cement interface, with no damage to the cement–formation interface. Inclusion of the pre-existing defect led to earlier damage initiation, at 2.75 days compared to 4 days, and produced a microannulus with over double the peak aperture at 0.077 mm compared to 0.037 mm. These findings emphasize the importance of accounting for initial defects and damage evolution when investigating the integrity of CO₂ injection wells.