Effect of Brine Composition on CO2/Limestone Rock Interactions during CO2 Sequestration

Mohamed, I.M., He, J., and Nasr-El-Din, H.A.
Presented at Journal of Petroleum Science Research 2(1)14-26, 2013.


Several parameters affect the chemical reactions between CO_2/fluid/rock: pressure, temperature, rock type, and brine composition. Brine composition includes salt concentration and type. Pink Desert limestone cores were used to conduct a series of coreflood experiments to address the effect of brine composition on the chemical reactions between carbonic acid and limestone rock. The experiments were designed to simulate the water alternating gas (WAG) injection of CO_2 into saline carbonate aquifers. Supercritical CO_2 and brines were injected at flow rates of 2 and 5 cm3/min at 70 and 200°F. Seawater, formation brine, calcium chloride, sodium chloride, and magnesium chloride brines were used in this study. A commercial compositional simulator was used to simulate the coreflood experiments at the lab conditions. The reaction rate constant of CO_2 with calcite at different brine compositions was adjusted to match the calcium concentration obtained in the lab. Experimental data was used to predict the reaction rate constant between CO_2/brine/rock and found to be increasing as the brine salinity increased (Log(k_(25))= ‐9.2) when CO_2 dissolves in DI water, and ‐6.2 when CO_2 dissolves in 5 wt% CaCl_2 brine). A simulation study conducted on field scale showed that after 30 years of CO_2 injection and 1400 years after injection stopped, brine composition does not affect the trapping mechanism of CO_2 in the aquifer.