Investigation on Nonfickian Model for Prediction of CO2 Diffusion Coefficient in water by Pressure Decay Method

Storage and dispose of CO2 in aquifers is a promising techniques to mitigate global warming and reduce greenhouse gases (GHG). Measurement of CO2 dissolution rate in saline aquifers is dependent on the finding an appropriate model for gas diffusion. Indirect methods, especially pressure decay, are currently being used to measure molecular diffusivity. The most important point in this method is the useage of appropriate model and analyze the experimental results. In this paper, non-Fick modeling method is used to analyze the experimental data of pressure decay method for CO2 emission in saline aquifers and the results are compared with Fick model with two different types of boundary conditions. For this purpose, by the inverse solution and minimizing the error function between the pressure-time values of the modeling and the experimental using optimization are estimated diffusion coefficient, mass transfer coefficient and delay time. The results show that with respect to the non-equilibrium boundary condition the diffusion coefficient was more than doubled compared to the equilibrium boundary condition and the non-equilibrium boundary condition is more consistent with the experimental results. On the other hand, the nonfickian model delays the equilibrium arrival with a delay time regulator term and is more consistent with the experimental results, especially in the early moments.