(415b) Evolution of Carbonate Dissolution Features Produced Under Variable pCO2 Conditions Relevant to CO2-EOR and Geologic CO2 Storage

The role of mineral and pore-scale heterogeneity was explored in this study by observing the development of dissolution features in relatively heterogeneous and homogeneous carbonate units from the Weyburn-Midale hydrocarbon reservoir (Saskatchewan, Canada). The Weyburn-Midale reservoirs are dominated by carbonate (calcite and dolomite ± anhydrite, quartz) mineralogies that will partially dissolve as the acidic CO₂-rich waters used in EOR operations react with formation rock, altering porosity and permeability. Our experimental study aimed to quantify the relationship between fluid flow, heterogeneity, and reaction specific to carbon storage at the Weyburn-Midale field by integrating characterization, pressure/permeability data, and solution chemistry. We chose to study the porosity evolution using fluids equilibrated at pCO₂ levels representative of those calculated from site monitoring data and carbonate units reflecting different initial mineral abundances, porosity distributions, and permeabilities  .We combine X-ray computed microtomography (XCMT) data with higher resolution scanning electron microscopy (SEM) images and statistical analysis to capture submicron pores to centimeter-scale or larger vugs. This methodology was chosen in an effort to use void space and mineral characterization of the carbonate cores before and after reaction to identify the type and mechanism of dissolution fronts in reactive systems.

Stable and unstable dissolution fronts in Marly dolostone and Vuggy limestone cores developed due to coupled flow and reaction processes, which were primarily affected and controlled by pore-scale heterogeneity.  Here we discuss the role of heterogeneity on the development of distinct reaction fronts relevant to enhanced oil recovery and carbon storage using this rich experimental dataset.  We utilize the data to rigorously constrain parameter input values such as kinetic rate constants and effective reactive surface areas to quantify relationships between dissolution and porosity production and evolving permeability in reactive-transport simulations of CO₂-carbonate interactions.