Geochemical Interpretation of In-Situ Carbonated Brine-Sandstone Interaction: Implications for CO2 Geo-Sequestration

Abstract Geo-sequestration of carbon dioxide (CO2) in underground geological formations is a highly endorsed method to mitigate existing greenhouse gas emissions. During this procedure, CO2 may dissolve in in-situ fluids (e.g., brine), producing a reactive solute (e.g., carbonated brine). Subsequently, chemical interactions may occur as the solute engages with the host rock, affecting its petrophysical characteristics and CO2 sequestration capacity. This work reports the findings of an integrated experimental and geochemical modeling investigation aimed at assessing the characteristics of mineral dissolution and potential alterations in the petrophysical properties of Berea Sandstone. A CO2-saturated brine (i.e., carbonated brine) was injected through Berea sandstone samples at elevated temperature (60 °C) and pressure (20MPa). The main objectives were to evaluate the fluid-rock geochemical reactions (e.g., mineral dissolution) and quantify changes in the porosity and permeability of the rock samples. The experimental study included the effluent brine collection followed by their geochemical analysis. Subsequently, such results were interpreted using geochemical reaction modelling done using the Geochemist’s Workbench package. The findings indicated a measurable decrease in post-flood permeability (~5mD ≈5%) due to the dissolution and subsequent precipitation of certain minerals, together with the blocking of pore throats. A little increase in sample porosity (~0.29%) was noted mostly as a result of the breakdown of clay and carbonate minerals. The geochemical reaction modelling revealed that the proper selection of the initial input and set-up parameters is of prime importance, which could improve the quality of the results and lead to a better evaluation of different chemical reactions. The geochemical model indicated that the calcite and albite were dissolved during carbonated brine flooding, and solution pH decreased from 8.5 to ~4.5 with increasing CO2 concentration in the system, while dawsonite minerals formed as a response to this dissolution.The amount of mineral dissolution could be accurately estimated using geochemical reactive modelling by carefully setting up the controlling parameters of the model. This signifies the complementary nature of experimental work and a well-set numerical simulation model.