Influence of Capillary Pressure and Injection Rate as well as Heterogeneous and Anisotropic Permeability on CO2 Transport and Displacement Efficiency in Water-Saturated Porous Media

Abstract

Greenhouse gas emission from industrial production and human living has been widely recognized as one of the primary reasons which cause global climate warming. CO2 sequestration in saline aquifers plays an important role in effectively reducing the greenhouse gas emission. Numerical modeling can be used to quantitatively analyze the effect of some formation properties on the storage processes of CO2 in saline aquifers. Magnetic resonance imaging (MRI) technology may be used to observe the evolution of CO2 plume through time in porous rocks and hence provide an effective means for validate the reliability of the numerical modeling. Based on a combined use of the numerical modeling and the MRI measurement of the vertical injection of the supercritical CO2 into water-saturated rock cores, this study presents a lab-scale investigation on the influence of the heterogeneous and anisotropic permeability, the CO2 injection rate and capillary pressure on the transport of CO2 plume as well as the CO2 utilization efficiency of subsurface space in saline aquifers. Our results indicate: 1) both the heterogeneity and the anisotropy of permeability can enhance the CO2 displacement efficiency. Ignoring these two permeability properties can cause the obvious deviation in the predicted CO2 saturation and transport processes by the model; 2) the enhanced sequestration efficiency by the anisotropy depends on the degree and spatial extension of itself. If the approximately stochastically distributed permeability anisotropy represents natural conditions, specifying the constant ratio of the vertical permeability to the horizontal one in the model to mimic the real permeability can lead to the obvious over-estimation of the CO2 displacement efficiency. Besides, the displacement front of the CO2 plume tends to pass through the region with the higher vertical permeability, thus forming the anomalistic shape of the displacement front; 3) the capillary pressure can influence the CO2 utilization efficiency in the rock core significantly, and tends to inhibit the movement of pore water, which accordingly lowers the CO2 displacement efficiency; 4) the CO2 injection rate can largely affect the CO2 displacement efficiency. The final CO2 saturation of CO2 in the rock core is notably enhanced with the increasing injection rate.