A critical review of CO₂ mineral trapping in sedimentary reservoirs – from theory to application: Pertinent parameters, acceleration methods and evaluation workflow

Prolonged increase in atmospheric concentration of CO₂ has led to global warming. One promising way to alleviate this problem is geological CO₂ storage (GCS) in sedimentary reservoirs. These reservoirs must meet certain criteria, such as sufficient storage capacity, injectivity, containment and enough depth to achieve supercritical conditions. Following injection, part of the CO₂ occupies the porous media in structural and/or stratigraphic traps, part is dissolved in water, part is trapped by capillary forces as residual CO₂, and, in case of favorable conditions, a portion may precipitate as carbonate minerals. Among above mechanisms, only the latter, known as CO₂ mineral trapping, guarantees permanent and safe CO₂ storage. This review presents an overview of GCS as a solution for mitigating global warming with a focus on the importance of CO₂ mineral trapping for permanent and safe storage. It discusses the mechanisms and factors influencing CO₂ mineral trapping kinetics, and presents methods for accelerating the process. The ultimate goal is to present a workflow for evaluating CO₂ mineral trapping potential in target sedimentary reservoirs. Laterally extensive, porous and permeable sedimentary units are the most desirable targets for GCS. However, the mineral trapping rates in these units are generally very slow, as in most reservoirs, it takes thousands of years to increase pH to a level necessary for CO₂ conversion into solid phase (normally pH greater than 9.0). Occurrence and rates of mineral trapping mostly depend on reservoir and fluid properties, such as the possibility for interaction of the CO₂ injection stream and reservoir brines, as well as mineralogy and texture of reservoir host rocks. There are some methods for acceleration of CO₂ mineral trapping: i) increase of CO₂ solubility by co-injection of bio-generated carbonic anhydrase and/or microbes (e.g., halophilic carbonate-forming bacteria, carbonic anhydrase bacteria, and urea bacteria); ii) identification and selection of sedimentary reservoirs with reactive minerals, such as ultramafic rock fragments; and iii) enhancement of reactive minerals surface area by fracturing. For evaluation of CO₂ mineral trapping potential in target reservoirs, a fit-for-purpose workflow is required, which includes evaluation of preliminary parameters for GCS, such as pressure, temperature, and caprock integrity, and comparative analysis of pertinent parameters for mineral trapping (primary screening), followed by thermal-hydrological-mechanical-chemical (THMC) simulation and experimental verification (advanced screening).