Anna L. Herring

Enhancing residual trapping of supercritical CO2 via cyclic injections

We utilize synchrotron x-ray tomographic imaging to investigate the pore-scale characteristics and residual trapping of supercritical CO2 (scCO2) over the course of multiple drainage-imbibition (D-I) cycles in Bentheimer sandstone cores. Capillary pressure measurements are paired with x-ray image derived saturation and connectivity metrics which describe the extent of drainage and subsequent residual (end of imbibition) scCO2 trapping. For the first D-I cycle, residual scCO2 trapping is suppressed due to high imbibition capillary number (Ca ≈ 10-6); however, residual scCO2 trapping dramatically increases for subsequent D-I cycles carried out at the same Ca value. This behavior is not predicted by conventional multiphase trapping theory. The magnitude of scCO2 trapping increase is hysteretic and depends on the relative extent of the sequential drainage processes. The hysteretic pore-scale behavior of the scCO2-brine-sandstone system observed in this study suggests that cyclic multiphase flow could potentially be used to increase scCO2 trapping for sequestration applications.

Pore-Scale Characterization of Two-Phase Flow Using Integral Geometry

The pore-scale morphological description of two-phase flow is fundamental to the understanding of relative permeability. In this effort, we visualize multiphase flow during core flooding experiments using X-ray microcomputed tomography. Resulting phase morphologies are quantified using Minkowski Functionals and relative permeability is measured using an image-based method where lattice Boltzmann simulations are conducted on connected phases from pore-scale images. A capillary drainage transform is also employed on the imaged rock structure, which provides reasonable results for image-based relative permeability measurements even though it provides pore-scale morphologies for the wetting phase that are not comparable to the experimental data. For the experimental data, there is a strong correlation between non-wetting phase Euler characteristic and relative permeability, whereas there is a weak correlation for the wetting phase topology. The relative permeability of some rock types is found to be more sensitive to topological changes than others, demonstrating the influence that phase connectivity has on two-phase flow. We demonstrate the influence that phase morphology has on relative permeability and provide insight into phase topological changes that occur during multiphase flow.