Uncertainty analysis for CO2 geological storage due to reservoir heterogeneity based on stochastic numerical model

Abstract

Due to uncertainties of permeability and porosity in actual heterogeneous saline aquifers, CO₂ geological storage exhibit the significant uncertainties for the critical parameters, such as horizontal migration distance, CO₂ dissolved amount, gas CO₂ amount per unit distribution volume and pore pressure. To investigate uncertainties for CO₂ storage, Sequential Gaussian method was introduced to generate stochastic fields of porosity and permeability, under which the governing equation for CO₂ geological storage was re-derived, to establish the stochastic numerical model, which was validated by theoretical solution by comparing CO₂ horizontal migration distance. By conducting the stochastic simulation, the effect of heterogeneity on CO₂ storage was concluded with the faster horizontal migration rate, farther horizontal migration distance, higher CO₂ dissolved amount, lower gas CO₂ amount per unit distribution volume and relatively smaller pore pressure compared to homogeneous model, indicating that the homogeneous model may be not accurate enough and would result in significant deviations in predicting the critical parameters for CO₂ storage in actual heterogeneous aquifers. Furthermore, the total of 100,000 times of stochastic numerical simulations was performed to determine uncertainties of critical parameters for CO₂ storage. The probability distributions and the expected values were obtained for critical parameters for CO₂ storage, and the confidence intervals of critical parameters were obtained under the confidence level of 95 %.