Modeling Solute Diffusion in the Presence of Pore-Scale Heterogeneity
A range of pore diffusivities, D{sub p}, is implied by the high degree of pore-scale heterogeneity observed in core samples of the Culebra (dolomite) Member of the Rustler formation, NM. Earlier tracer tests in the culebra at the field-scale have confirmed significant heterogeneity in diffusion rate coefficients (the combination of D{sub p} and matrix block size). In this study, expressions for solute diffusion in the presence of multiple simultaneous matrix diffusivities are presented and used to model data from eight laboratory-scale diffusion experiments performed on five Culebra samples. A lognormal distribution of D{sub p} is assumed within each of the lab samples. The estimated standard deviation ({sigma}{sub d}) of In(D{sub p}) within each sample ranges from 0 to 1, with most values lying between 0.5 and 1. The variability over all samples leads to a combined {sigma}{sub d} in the range of 1.0 to 1.2, which appears to be consistent with a best-fit statistical distribution of formation factor measurements for similar Culebra samples. A comparison of the estimation results to other rock properties suggests that, at the lab-scale, the geometric mean of D{sub p} increases with bulk porosity and the quantity of macroscopic features such as vugs and fractures. However, {sigma}{sub d} appears to be determined by variability within such macroscopic features and/or by micropore-scale heterogeneity. In addition, comparison of these experiments to those at larger spatial scales suggests that increasing sample volume results in an increase in {sigma}{sub d}.
- Research Organization:
- Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Sandia National Lab. (SNL-CA), Livermore, CA (United States)
- Sponsoring Organization:
- US Department of Energy (US)
- DOE Contract Number:
- AC04-94AL85000
- OSTI ID:
- 13998
- Report Number(s):
- SAND99-1947J; TRN: AH200135%%534
- Journal Information:
- Journal of Contaminant Hydrology, Other Information: Submitted to Journal of Contaminant Hydrology; PBD: 21 Oct 1999
- Country of Publication:
- United States
- Language:
- English
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