Coupled Flow and Wellbore-Integrity Geomechanical Effects During Continuous and Cyclic CO2 Injection

Abstract The sealing potential of the caprock, wellbore and storage formation integrity, are critical elements to ensure CO2 containment and the success of carbon capture storage (CCS) projects. Injection of CO2 for geological storage, results in cooling and increase of pore pressure leading to mechanical deformation in the wellbore cement, reservoir and caprock, which over time can cause leakage due to potential rock failure and irreversible damage. The CO2 chemical interaction with the rock and cement may also lead to mechanical alteration. Coupling thermodynamics, and fluid flow with deviated stress conditions is important for understanding and predicting the geomechanical behaviour of the wellbore, reservoir and caprock formations. This complex interaction was studied with GEM simulator from CMG using dedicated 3D and 2D reservoir models. The study was performed in multiple steps. First, laboratory experiments on the impact of pressure-temperature cyclicity on well integrity were simulated. Results indicated validity of the modelling concept and allowed proper design and constrains of the reservoir scale model for the second step of the study. Due to computational complexity, simulation of geochemical reactions was excluded. The impact of CO2 injection on the geomechanical properties of the cement and rock was approximated by tabulated dependency of Young’s modulus and cohesion against CO2 saturation. Overall, the results showed that the main failure type in the near-wellbore region is probably tensile, accounted by the tensile safety factor (TSF), extending laterally up to 20 m in the reservoir rock and 1 m in the caprock. The cement also experiences tensile failure up to 3 m in the vertical direction, and above that the TSF tends to increase steadily, posing no risk to wellbore integrity. Shear failure is not expected.