Role of permeability evolution induced by CO₂ injection on CO₂ storage and CH₄ production in a low permeability reservoir

CO₂-injection induced geochemical reactions exert important influence on CO₂ enhanced shale gas recovery by altering the shale porosity and permeability. This impact, however, has been seldomly quantified. To identify and quantify the role of CO₂-water-rock reactions in the evolution of shale permeability and its influence on CH₄ production and CO₂ sequestration, a multi-components reactive transport model for low permeability media (10⁻²² - 10⁻¹⁸ m²) is established by coupling the geochemical and geomechanical effects of CO₂ injection on rock porosity and permeability. The effect of CO₂ dissolution and induced geochemical reactions on CH₄ production and CO₂ storage is then explored with experiments and numerical simulations. A sensitivity analysis is conducted to identify the uncertainties induced by the inherent shale and engineering factors. Results show that a very limited variation in porosity and permeability (<1 %) induced by the CO₂-water-rock reactions could cause significant perturbation in CH₄ production and CO₂ sequestration in shale by controlling the pressure perturbation in the reservoir and the CO₂ migration. These impacts dynamically change with the extent and degree of geochemical reactions (e.g. mineral dissolution/precipitation), with up to 17 % for CH₄ production and 24 % for CO₂ storage at the conditions considered in this study. High pressure-temperature (10–15 MPa, 40–80 °C), low matrix permeability (0.001–0.1 mD) and injection rate (0.05–0.2 kg/s) strengthen the influence by aggravating the degree of CO₂-water-shale reaction. While high injection rate and matrix permeability can enhance the impact by promoting CO₂ migration, they can also increase the leakage risk of CO₂. This study provides the development of a practical methodology for the CO₂ reactive transport modeling as well as the theoretical support for development of unconventional resources and CO₂ storage in low permeable reservoirs.