(743b) Effects of Carbonated Brine-Rock Interactions on Multiphase Flow Properties in Heterogeneous Sandstone

With the injection of CO₂ into a deep saline aquifer, CO₂ can dissolve in the in-situ brine to form carbonic acid, which drives fluid-rock geochemical reactions. The impacts of these fluid-rock geochemical reactions on porosity, permeability, and multiphase flow responses in rock are important to evaluate CO₂ storage capacity in deep saline aquifers. However, such investigations on heterogeneous eolian sandstone, consisting of poorly sorted, quartz-rich sand with laminated bedding, have been rare.

In this research, carbonated brine injection experiments were performed on core samples from the Upper Minnelusa Formation at the Wyoming CarbonSAFE project site located in Northeast Wyoming. The core samples exhibit heterogeneity consisting of poorly sorted sand with laminated bedding. Complementary pre- and post-injection porosity, permeability, SEM, thin section, Mercury Intrusion Capillary Pressure (MICP), and Brunauer-Emmett-Teller (BET) surface area were measured to study the petrophysical properties changes. Overall, porosity and permeability of the core sample both increased significantly after experiencing 7-day carbonic acid injection, from 6.2% to 8.4% and 1.6mD to 3.7mD, respectively. We attributed these changes to mineral dissolution, which was confirmed by the effluent brine geochemistry, pore throat size distribution resulting from MICP, and BET surface area. To be more specific, the more permeable section of core sample owes larger pore size, the permeability increment of this section is apparent due to dolomite cement dissolution, as shown by SEM and thin section. However, within the less permeable rock section, the smaller pore size and possible mineral precipitation lessened dissolution resulting insignificant petrophysical properties changes. Consequently, the observed heterogeneous carbonated brine-rock interactions resulted in alterations of CO₂/brine relative permeability, i.e. a decrease from 0.29 to 0.2 in CO₂ saturation at irreducible water saturation, while CO₂ relative permeability increased as a whole. The work in this study provides a fundamental understanding of the effect of fluid-rock reactions on the changes in static and multiphase flow properties, which lays the foundation for accurate prediction/simulation of CO₂ injection into deep saline aquifers. This work is funded under the Department of Energy CarbonSAFE program (awards DE-FE0031624 DE0031891).