MODELING OF MINERAL TRAPPING FOR CO2 SEQUESTRATION

Abstract

In order to prevent CO₂ concentrations in the atmosphere from rising to unacceptable levels, carbon dioxide is sequestered beneath the ground surface. CO₂ can be trapped as a gas under a low-permeable cap rock (structural trapping) or can dissolve into the ground water (hydrodynamic trapping); it can also react with minerals and organic matter that are dissolved in the brine to form precipitates (mineral trapping). From the perspective of secure, long term storage, mineral trapping has been identified as the most effective mechanism related to subsurface sequestration. Temperature, pressure and salinity are among the primary parameters governing the overall behavior of the process of mineral trapping. In this study, the primary goal is to simulate the behavior of carbon dioxide with an improved model under the conditions of temperature and pressure typical of saline aquifers, i.e. 50 to 100<super>o</super>C and 1-500 bar, respectively. The objective is to determine how the related quantities of molar volume as well as CO₂ fugacity change in response to changes in pressure and temperature so that the associated changes in the solubility and the precipitation of carbonates, indicating the rate of CO₂ consumption, can be quantified. This study finds that the dissolution rate of anorthite and the rate of precipitation of calcite both rise with the increase in pressure and temperature. The dissolution rate of anorthite has been found to be the rate-limiting process in the sequestration of CO₂ and governs the consumption rate of CO₂ in the aqueous phase. These results show good agreement with those obtained from experimental work reported in other studies. This study also agrees earlier findings based on relatively less precise models, with respect to the increase in CO₂ solubility at higher pressures and a decrease in solubility associated with increasing values of temperature and salinity.