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

Abstract

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).