An Open-access Well Integrity Tool to Study Legacy Wells Re-Purposed for CO2 Injection

This work presents a well integrity tool based on an analytical model describing the thermo-poroelastic behaviour of wells in the so-called drained conditions and plane-strain conditions. The analytical model takes into account the pore pressure, uniform temperatures changes across the well and the cement's initial state of stress. The well integrity tool estimates the potential for debonding, tensile and shear fracturing of the rock and the cement sheath using computed stress profiles and the Mohr-Coulomb failure criterion. The tool is suited to study vertical well sections consisting of a single casing and cement sheath inside a porous or non-porous rock formation. The tool is built within a Microsoft Excel spreadsheet to make it as accessible, portable and flexible as possible. Furthermore, this work also presents an integrity analysis of a characteristic gas production well re-purposed for CO2 injection. This investigation covers the construction of the well, reservoir depletion, CO2 injection and long-term storage conditions. This demonstrates the type of data necessary for the tool to function, the different results and outputs that may be expected and the type of conclusions that may be drawn from them. This work is part of wider efforts by TotalEnergies to drive the development of safe CO2 storage technology and in particular to progress the understanding of well integrity loss mechanisms.