Well Injectivity during CO₂ Geosequestration: A Review of Hydro-Physical, Chemical, and Geomechanical Effects

Abstract

Deep saline aquifers are among the most favorable geological sites for short- and long-term carbon geosequestration. Injection of CO2 into aquifers causes various hydro-physical, chemical, and geomechanical interactions that affect the injectivity of wellbores. Despite the extensive research conducted on carbon capture and storage (CCS), there exists a lack of focus on the concept of injectivity. The present study aims to identify the gaps by reviewing the major factors contributing to CO2 injectivity in deep saline aquifers. Moreover, the existing analytical and numerical mathematical models to estimate maximum sustainable injection pressure and pressure build-up are critically reviewed. Concerning the analytical models, the main controversies are related to the general shape of the CO2–brine interface that stems from neglecting or assuming CO2 compressibility, mutual solubility of CO2 and water, and drying-out effects. Besides, the models predicting waterflooding processes cannot accurately evaluate the injectivity of CO2 due to the unique features of CO2. Furthermore, most models have concentrated on CO2 storage capacity at the reservoir scale and not on wellbore injectivity. Thermo-poro-elastic effects influencing the in situ stresses and constraining the maximum sustainable injection pressures are also neglected in some cases. Despite the numerous numerical modeling workflows or tools, some mechanisms have not yet gained the desired attention, especially the chemical aspects of CO2-rich brine. Finally, while the field data demonstrate the applicability of CO2 geosequestration in saline aquifers, regular wellbore injectivity monitoring and surveillance is deemed necessary.

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