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 CO 2 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 CO 2 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 CO 2 −brine interface that stems from neglecting or assuming CO 2 compressibility, mutual solubility of CO 2 and water, and drying-out effects. Besides, the models predicting waterflooding processes cannot accurately evaluate the injectivity of CO 2 due to the unique features of CO 2 . Furthermore, most models have concentrated on CO 2 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 CO 2 -rich brine. Finally, while the field data demonstrate the applicability of CO 2 geosequestration in saline aquifers, regular wellbore injectivity monitoring and surveillance is deemed necessary.

Influence of Injection Well Location on CO2 Geological Storage Efficiency

“…However, Stopa et al [33] developed computational methods to optimize the location of the injection well for a different purpose, namely, to minimize the risk of CO 2 leakage. Hajiabadi et al [34] also emphasized that most models have focused on reservoir-level CO 2 storage capacity rather than well injectivity and attempted to identify the gaps by examining the significant factors contributing to CO 2 injectivity in deep saline aquifers. In turn, Okwen et al [35] performed numerical simulations of CO 2 injection to evaluate the gas storage efficiency for different sedimentation environments at five different CO 2 injection well locations.…”

Advances in Carbon Dioxide Storage Projects: Assessment and Perspectives

“…In attempts at these enormous increases, various countries are aware of the future impact of high concentrations of CO 2 on the atmosphere. The Intergovernmental Panel on Climate Change (IPCC) suggested limiting global warming to 1.5 °C rather than 2.0 °C to mitigate the serious consequences of climate change problems to attain a concentration of CO 2 , which is less than 350 ppm, as recommended by the comprehensive studies. , The European Union (EU), together with G8 countries, have suggested limiting CO 2 and other global GHG emissions into the atmosphere to a minimum of 80% between 1990 and 2050 . However, the awareness of carbon-intensive countries has become increasingly important in the mitigation of excess CO 2 to the atmosphere by conducting carbon capture and storage (CCS) techniques …”

Review on Geopolymers as Wellbore Sealants: State of the Art Optimization for CO2 Exposure and Perspectives

“…Carbon capture and storage (CCS), with storage in porous geological reservoirs of sedimentary origin, is considered a key technology for the mitigation of climate change. − An important challenge for geological CO 2 storage is the integrity of the wells used during CO 2 -injection (as well as potential pre-existing wells). The main risk to the sealing integrity of these wells is leakage through the cement matrix or along the cement-formation and cement-steel interfaces, which could lead to the uncontrolled release of the injected CO 2 . − In most CCS operations, CO 2 is injected to a depth of 800 m or greater, where required conditions for the supercritical state of CO 2 (scCO 2 ) are met (i.e., pressures greater than 7.38 MPa and temperatures above 31.04 °C).…”