Effect of CO2 solubility on dissolution rate of calcite in saline aquifers for temperature range of 50-100 degrees C and pressures up to 600 bar: alterations of fractures geometry in carbonate rocks by CO2-acidified brines

摘要

An empirical model is developed to predict the dissolution rate of calcite in saline solutions that are saturated with respect to dissolved CO2 over a broad range of both subcritical and supercritical conditions. The focus is on determining the rate of calcite dissolution within a temperature range of 50-100 degrees C and pressures up to 600 bar, relevant for CO2 sequestration in saline aquifers. A general reaction kinetic model is used that is based on the extension of the standard Arrhenius equation with an added, solubilitydependent, pH term to account for the saturated concentration of dissolved CO2. On the basis of this kinetic model, a new rate equation is obtained using multi-parameter, nonlinear regression of experimental data to determine the dissolution of calcite as a function of temperature, pressure and salinity. Different models for the activity coefficient of CO2 dissolved in saline solutions are accounted for. The new rate equation helps us obtain good agreement with experimental data, and it is applied to study the geochemically induced alterations of fracture geometry due to calcite dissolution.