Characterization of local capillary trap clusters in storage aquifers

Abstract

Local capillary trapping occurs when buoyant CO2 moves upward in a saline aquifer during geologic carbon sequestration. The volumetric capacity of local capillary traps (LCTs) is controlled by reservoir geological heterogeneity. These traps are thus intrinsic to heterogeneous storage aquifers; their volumetric capacities are however largely unknown. To address this issue, this work employs an easily calculated criterion that requires only a static geologic model to estimate the properties of LCT clusters, including size, frequency, and extent. Specifically, this work quantitatively analyzes: i) the properties of the largest LCT cluster; and ii) the impact of reservoir heterogeneity on cluster properties. The key finding of this work is that spatially-correlated reservoir heterogeneity in the horizontal direction causes the largest LCT cluster to laterally span across a given domain even when the horizontal correlation length is small (only 1/25th) compared to the domain width. The overall work sheds useful insights of the dependence of LCT clusters on reservoir heterogeneity and its implication for CO2 trapping quantification.