Heterogeneity Influence on Geological CO2 Storage within Carbonate Saline Aquifers

Abstract The ongoing decarbonization efforts can be achieved by capitalizing on geological CO2 storage, for which carbonate saline aquifers can be feasible candidates. Since carbonate formations tend to have a myriad of geological complexities, reservoir modeling and simulation facilitate the storage process by depicting the CO2plume and distribution. This paper investigates the role of various degrees of geological heterogeneity in CO2 storage within carbonate saline aquifers. A three-dimensional carbonate aquifer model examined a plethora of heterogeneities by capitalizing on Dykstra-Parsons permeability variation. Numerical simulation was employed to estimate the CO2 distribution and migration path over a 200-year storage period. Numerous scenarios were developed to parameterize the impact of the heterogeneity severity along with different autocorrelation lengths on the free, dissolved, and trapped CO2 levels. Vertical permeability to horizontal permeability ratios (KVKH) of 0.5, 1.0, and 2.0 were sensitized to investigate the vertical CO2 distribution during CO2 injection. In addition to the KVKH, permeability streaks were also captured in the analysis. Incorporating a broad spectrum of permeability variations helps determine the long-term impact of heterogeneity on the CO2 storage process. The developed analyses expound on the influence of geological heterogeneity in the storage process. Generally, KVKH can significantly impact CO2 distribution in the aquifer. The dissolved CO2 increases as KVKH increases. The change occurred due to the potential to transfer an additional volume of dissolved CO2 to the bottom of the aquifer. Heterogeneity severity with the same KVKH can affect the trapped CO2in the short term, but long-term distribution tends to be similar. For example, a KVKH of 2.0 yields a similar CO2 inventory after 200 years of storage, regardless of the degree of heterogeneity. Hence, high KVKH can potentially mask the heterogeneity effects in the long term. Moreover, the autocorrelation length can have a higher influence than the degree of heterogeneity. The CO2 distribution depends on permeability continuity since it has the potential to control subsurface flow dynamics. When permeability streaks exist, the CO2 inventory exhibits similar trends to those of high KVKH. Overall, the vertical permeability demonstrated substantial influence on the CO2 storage compared to variable degrees of heterogeneity. Applying various degrees of heterogeneities provides a comprehensive evaluation of the CO2 distribution within carbonate saline aquifers throughout the storage lifecycle. Hence, contributes to depicting the migration path of the CO2 plume while incorporating the influence of heterogeneity, enabling long-term CO2 storage optimization.