Understanding the Influence of Pore-Scale Structural Heterogeneity in CO2 Geosequestration

Abstract

1. Introduction Predicting the behavior of CO2-brine in the complex heterogeneous porous structure of reservoir rocks as well as the interaction between these fluids with minerals in rocks are important for designing and managing CO2 storage sites in Carbon Capture and Storage technology. To increase the effectiveness of the underground CO2 sequestration, the multiphaseflow and its relevant mechanisms that change the distribution and concentration of the underground CO2 must be assessed. To date, CO2 geosequestration as a complex multiphase fluid flow in heterogeneous rock systems has not yet been given enough attention due to various reasons including lack of high quality experimental data, coupled fluidfluid-rock interaction that is made even more complex due to rock heterogeneity, difficulty of insitu experimentation and acquisition of usable data etc. The focus of this research is directed towards understanding the role of rock heterogeneity on the safety and capacity of CO2 geo-sequestration at the pore and core scales.

2. Materials and Methods We will present a pore-scale tomographic and experimental study of CO2 trapping mechanism in heterogeneous sandstone. The in-situ experiments consist of multiple sets of drainage and imbibition experiments on three sandstone rocks with different types of heterogeneities. High resolution X-ray micro Computed Tomography (XCT) scans were acquired to resolve pore scale features and fluid distribution in the system. The experimental setup [1] is composed of a high pressure/temperature triaxial flow cell for in-situ flow experiments.

3. Results and Conclusion Rock heterogeneity at the pore scale can be mapped in 3D and we have correlated rock morphology with multiphase fluid distribution. Our results show larger amounts of trapped scCO2 in heterogeneous rock compare with the homogeneous ones at a high rate. Residual scCO2 are mostly trapped in pores with larger radii with high aspect ratios. We have also conducted insitu cyclic brine-CO2 flooding experiments, and our results show that residual CO2 accumulates in layers parallel to the low-perm lamination layers, and primarily below the layers present in the rock. These results agree with the conceptual model that the cyclic fluid injection creates a preferential high-flow pathway below the low-perm layer [2]. We observe that at low flow rates; the capillary trapped CO2 increases in volume as the number of injection cycle increases, however, at high flow rates, lower residual trapping of CO2 is observed. Show more