Title: Single and Multiple Rates of Nonequilibrium Diffusive Mass Transfer at the Laboratory. Field and Regional Scales in the Culebra Member of the Rustler Formation, New Mexico. Abstract Approved:

In the first phase of this study, data from eight laboratory-scale diffusion experiments performed on five samples of the Culebra (dolomite) Member of the Rustler Formation, New Mexico, are examined for evidence of variability in effective diffusion coefficients. Modeling is performed under the assumption of a lognormal distribution of D, The estimated standard deviation (6d) of ln(De) within each sample is found to range from 0 to 1, with most values lying between 0.5 and 1. The variability over all samples leads to a combined ad in the range of 0.9 to 1.2. Formation factors measured on Culebra samples are found to be well-described by a lognormal distribution with a standard deviation of approximately 0.7. As formation factor is linearly related to D this implies: (1) the assumption of a lognormal distribution of De is appropriate; (2) our estimates of ad are reasonable; and (3) formation factors may provide an inexpensive means of characterizing variability in De. A comparison of our estimation results to other rock properties suggests that, at the lab-scale, the geometric mean of D, increases with bulk porosity and the quantity of macroscopic features such as vugs and fractures. However, ad appears to be determined by variability within such macroscopic features and/or by micropore-scale heterogeneity. In addition, comparison of experiments at several spatial scales suggests that increasing sample volume results in an increase i