Highlights 1 • Reports a large 3D benchmark study of pore-scale modeling methods 2 • Codes and methods varied widely in complexity and computational 3 demand 4 • Both macroscopic and local measures of flow and solute transport were 5 evaluated 6 • Comparisons were generally favorable among the various methods 7 • Differences observed support method selection depending on problem 8 context 9 Abstract 21Multiple numerical approaches have been developed to simulate porous media fluid flow and solute transport at the pore scale. These include 1) methods that explicitly model the three-dimensional geometry of pore spaces and 2) methods that conceptualize the pore space as a topologically consistent set of stylized pore bodies and pore throats. In previous work we validated a model of the first type, using computational fluid dynamics (CFD) codes employing standard finite volume method (FVM), against magnetic resonance velocimetry (MRV) measurements of pore-scale velocities. Here we expand that validation to include additional models of the first type based on the lattice Boltzmann method (LBM) and smoothed particle hydrodynamics (SPH), as well as a model of the second type, a pore-network model (PNM).The PNM approach used in the current study was recently improved and demonstrated to accurately simulate solute transport in a two-dimensional experiment. While the PNM approach is computationally much less demanding than direct numerical simulation methods, the effect of conceptualizing complex three-dimensional pore geometries on solute transport in the manner of PNMs has not been fully determined. We apply all four approaches (FVM-based CFD, LBM, SPH and PNM) to simulate pore-scale velocity distributions and (for capable codes) nonreactive solute transport, and intercompare the model results. Comparisons are drawn both in terms of macroscopic variables (e.g., permeability, solute breakthrough curves) and microscopic variables (e.g., local velocities and concentrations). Generally good agreement was achieved among the various approaches, but some differences were observed depending on the model context. The intercomparison work was challenging because of variable capabilities of the codes, and inspired some code enhancements to allow consistent comparison of flow and transport simulations across the full suite of methods. This study provides support for confidence in a variety of pore-scale modeling methods, and motivates further development and application of pore-scale simulation methods.
Geological storage of CO 2 (GCS), also referred to as carbon sequestration, is a critical component for decreasing anthropogenic CO 2 atmospheric emissions. Stored CO 2 will exist as a supercritical phase, most likely in deep, saline, sedimentary reservoirs. Research at the Center for Frontiers of Subsurface Energy Security (CFSES), a Department of Energy, Energy Frontier Research Center, provides insights into the storage process. The integration of pore-scale experiments, molecular dynamics simulations, and study of natural analogue sites has enabled understanding of the efficacy of capillary, solubility, and dissolution trapping of CO 2 for GCS. Molecular dynamics simulations provide insight on relative wetting of supercritical CO 2 and brine hydrophilic and hydrophobic basal surfaces of kaolinite. Column experiments of successive supercritical CO 2 /brine flooding with highresolution X-ray computed tomography imaging show a greater than 10% difference of residual trapping of CO 2 in hydrophobic media compared to hydrophilic media that trapped only 2% of the CO 2 . Simulation results suggest that injecting a slug of nanoparticle dispersion into the storage reservoir before starting CO 2 injection could increase the overall efficiency of large-scale storage. We estimate that approximately 22% ± 17% of the initial CO 2 emplaced into the Bravo Dome field site of New Mexico has dissolved into the underlying brine. The rate of CO 2 dissolution may be considered limited over geological timescales. Field observations at the Little Grand Wash fault in Utah suggest that calcite precipitation results in shifts in preferential flow paths of the upward migrating CO 2 -saturated-brine. Results of hybrid pore-scale and pore network modeling based on Little Grand Wash fault observations demonstrate that inclusion of realistic pore configurations, flow and transport physics, and geochemistry are needed to enhance our fundamental mechanistic explanations of how calcite precipitation alters flow paths by pore plugging to match the Little Grand Wash fault observations.
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