Small-scale Heterogeneities and Buoyancy-driven CO2 Migration in Geological Storage

Abstract

It is well understood that spatially correlated heterogeneities can affect large-scale CO₂ migrations in geological sequestration. However, recent experimental observations from high resolution Computed Tomography (CT) imaging have shown heterogeneities at the millimeter scale in natural sandstone core samples. These heterogeneities have a high degree of randomness without distinct spatial patterns, and they appear relatively homogeneous at a larger scale. As a result, such heterogeneities tend to be ignored in core analysis and in flow simulations. In this study, we show that ignoring such small-scale heterogeneities can lead to significant overestimations of CO₂ plume speed in modeling buoyancy-driven CO₂ migrations. For the representative examples we study, the overestimation can be a factor of two or larger.