Simulation of CO2 hydrate formation in porous medium and comparison with laboratory trial data

The storage of CO2 in gas hydrate form in the pore space in depleted natural gas reservoirs has been considered a method for greenhouse gas control. The formation of CO2 hydrate in porous medium is a strongly coupled Thermal-Hydraulic-Chemical (THC) problem under certain thermodynamic conditions. In this study, laboratory data on CO2 hydrate formation in silica sand, including the profiles of pressure, temperature, the amount of CO2, H2O, and CO2 hydrate, etc., were compared with results from numerical simulations. The minimized deviations between the simulation and experimental results, including the pressure drop, the significant temperature increase caused by hydrate formation, and the amount of CO2, water, and hydrate, were all less than 10 % in the numerical simulations. The sensitivities of the deviations between numerical simulations and experimental data to the domain discretization, thermal conductivity of the silica sand, absolute permeability, and kinetics of CO2 hydrate formation were analyzed. One of the major findings is that CO2 hydrate formation in the porous medium in this study is dominated by the kinetics of chemical reaction, rather than the heat or mass transfer. Another key finding of this study is the acquisition of the modeling parameters of the CO2 storage process in the laboratory-scale sand reservoir, including the thermal conductivity of the silica sand lambda s = 2.2 W/m/K, the absolute permeability k0 = 3.0 x 10(-11) m(2), and the kinetic constant Kf0 = 8.4 x 10(11) kg/m(2)/Pa/s and the reduction exponent beta = 5.3 in the kinetic model of CO2 hydrate formation. It is noteworthy that the mathematical models and the parameters faithfully fit three independent experiments of Run 1-3. The results of the experiments and corresponding numerical simulations provide a reliable method to evaluate the capacity, technical and commercial feasibility of CO2 storage in marine and permafrost reservoirs.