Capturing Clay-CO2 Interactivity via Water Analysis for CO2 Storage Applications

This study investigates the effect of brine/CO2 interactions with clay-rich (montmorillonite-rich, and illite-rich) formations, via water analysis using Capillary Electrophoresis. When considering CO2 storage in clay rich reservoirs, one needs to consider the reaction between clay, brine, and CO2. This reaction is complex and controlled by many factors, including the brine salinity and its ionic composition. The reaction between clay/brine/CO2can lead to dissolution of clay minerals, which leads to changes in the reservoir's physical properties (e.g., porosity and permeability), impacting the reservoir's storage capacity. In this study, two clay samples were considered, montmorillonite and illite. The clay samples, of know volume, were added separately to deionized water and NaCl brines of different salinities (i.e. 0, 5, 30, 40, 50, and 60 kppm), with and without dissolved CO2. The clay samples were given 24 hr to interact spontaneously in the various fluids. The clay/fluid and CO2/clay/fluids interactions were captured and analyzed using capillary electrophoresis method. The analysis results demonstrated that montmorillonite and illite are reactive with both DI water and NaCl brines with different salinities. We observed that the lower the brine salinity, the higher the interaction/dissolution of the clay minerals was. In addition, clay mineral dissolution in the presence of CO2 was more pronounced for both types of clays because of the formation of carbonic acid which enhances the clay mineral dissolution. Montmorillonite demonstrated greater reactivity than illite because it has greater cation exchange capacity, greater surface area as well as higher swelling potential. The results and findings of this study offer important information for the prediction of long-term CO2 storage in montmorillonite-rich and illite-rich reservoirs.