PNNL

Abstract

In the quest for net-zero greenhouse gas emission, CO2 capture and storage technologies play a prominent role. Estimates suggest a potential of sequestering up to several thousand metric gigatons of CO2. However, some of the main challenges in its development are an assessment of reservoir-specific storage capacities due to variabilities and heterogeneities in the underlying properties (structure, formations, facies, petrophysics, reservoir architecture, and others) and understanding the migration of CO2 in the subsurface. How much CO2 can be stored in a reservoir, and how quickly can it be injected? What will be the dominant storing (trapping) mechanisms? These questions, among others, remain as challenges to the commercial deployment of this technology. This article critically investigates CO2 plume characteristics and determines the evolving contributions of different trapping mechanisms during a 100-year injection period. Simulation results on the CO2 plume dynamics indicate that lateral propagation is much larger than vertical propagation. The ratio of average lateral to vertical dispersion ranged between 6.3 and 18.8 for the cases investigated. On average, for all the scenarios investigated, the free phase (mobile supercritical CO2) is the dominant trapping mechanism (in terms of the amount of CO2 stored) during the injection period, accounting up to 45% of the CO2 injected. Both residual (30%) and solubility (25%) trapping storage ratios decline with time during injection, and no significant mineral trapping appeared during the 100-year injection period. However, the behavior of CaCO3 suggests a predominant dissolution of CaCO3, especially in the vicinity of the injection well.