Dual Domain Transport Modeling

 

For field-scale transport through unconsolidated sediments, small-scale advection likely controls mass transfer between "mobile" and "immobile" regions. Adequate mechanistic approaches for defining optimal dual-domain parameter values in this setting have not been developed and/or validated. Our objective is to relate mobile-immobile region partitioning and the first-order mass transfer coefficient to readily characterized system parameters, such as facies and permeability distributions and hydrologic conditions. We hypothesize that such relationships exist and can be developed from a series of carefully designed numerical experiments.           To illustrate the feasibility of the concept, consider a perfectly layered system comprised of high and low permeability intervals, with a mean hydraulic gradient not parallel to the bedding planes. In this situation, flow in high conductivity zones is mostly parallel to the bedding, while flow in the low permeability zones is roughly normal. In the context of a two-region model, advective transport into and out of the low conductivity “immobile” regions plus diffusion is described by Equation (1), which could provide a mechanistic basis for choosing an optimal two-region mass transfer coefficient.

Under more realistic conditions, we anticipate a more complex relationship than Equation (1), but nonetheless one that can be deduced from numerical experimentation. We intend to perform such experiments and then validate (or invalidate) the inferred “optimal” dual-domain parameter settings through comparison to concentration data acquired from both high (mobile) and low (immobile) conductivity intervals at the P-Area Reactor field site.

Equation 1