Diffusion Behaviors of Na in Natural Porous Media
Abstract
Understanding transport behavior of key ionic species in porous media is critical to the evaluation of water-rock interaction in subsurface systems for energy resources, environmental remediation, and Geologic Carbon Storage (GCS). Development of predictive models for molecular-to-pore-scale processes in fluid-rock systems is necessary to quantify the dynamic processes relevant for complex heterogeneous systems, and this can be achieved by accurate and precise experimental measurements, physicochemical modeling, and their analysis. Using Nuclear Magnetic Resonance (NMR) techniques we investigated the diffusion of water and key dissolved sodium species in porous media as a function of dissolved species, ionic strength, and pore types and size. Sodium is an NMR active nucleus and is important due to its dominance in brine and natural groundwater systems. We use Indiana limestone (2-4 and 70 mD) as an example of natural porous media, and water as a freely diffusible tracer and carrier to demonstrate effective diffusion measurement of sodium based on changes in T2 relaxation time signal in pore confinement. Sodium diffusion coefficients are estimated via spin-spin relaxation time (T2) and Pulsed Field Gradient (PFG) measurements. Also, T2 relaxation time associated with pore geometry is studied using MRI coupled with μ-XCT (Micro X-ray Computed Tomography) imaging analysis. Complementing the experiments, we use the fluid-rock transport code, Crunchflow, to test diffusion behavior in porous media based on 3-D image reconstruction. The modeling takes into account the influence of confinement, tortuosity, and pore-wall adsorption. These experimental studies underpin existing empirical diffusion data and can be used in simulations to quantify behavior in more complicated systems.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.H21J1865H
- Keywords:
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- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCES;
- 0466 Modeling;
- BIOGEOSCIENCES;
- 1828 Groundwater hydraulics;
- HYDROLOGY;
- 1849 Numerical approximations and analysis;
- HYDROLOGY