Effect of temperature on the geological sequestration of CO_2 in a layered carbonate formation

摘要

Geological sequestration of CO_2 is one of the most promising technologies for large-scale CO_2 mitigation. To assess the suitability of a potential CO_2 storage site, we must understand the thermodynamics and kinetics of the CO_2-brine-rock system under the relevant conditions. Temperature can play a significant role in geochemistry, because it can affect phase equilibria in a multicomponent system and can impact reactive transport processes during geological carbon storage. In this study, we have assessed the effect of formation temperature on geological storage in a heterogeneous carbonate formation. The objectives of the numerical study are to quantitatively estimate the effect of temperature on 1) storage efficiency; 2) solubility trapping of CO_2 3) change in pH of residual brine; 4) changes in the mineralogy and porosity. Using TOUGHREACT 3.3 (a reactive transport simulator), we have estimated the changes in physical and chemical properties of a layered carbonate formation as a function of temperature. Mineralogy and physical properties of the aquifer are based on the Dollar Bay formation, a limestone dolomitic aquifer located within the South Florida Basin. We ran simulations for seven values of temperature, 35, 45, 55, 65, 75, 85 and 95°C. Results from the study suggest that density of supercritical CO_2 decreases with increase in temperature which leads to higher buoyancy at elevated temperatures. Therefore, storage efficiency of the aquifer decreases as temperature increases. For instance, an increase in temperature from 35°C to 95°C results in 65% decrease in storage efficiency. However, solubility trapping of CO_2 increases with an increase in temperature because the interfacial area increases with temperature. After the simulation period, pH drop was slightly more in case of higher temperature conditions. Temperature effect on porosity change was minimal and non-significant. The study can be helpful in screening a reservoir for geological carbon storage based on initial formation temperature.