Dead-End Pore Volume and Dispersion in Porous Media

Abstract

Experiments in 'wbr'cb calcium chloride displaced sodi~m chloride from four cores showed the extent of asymmetry in the resulting effluent concentration profiles.These results provided a check on bow validly the mixing process is modeled by a differential "(i.e., not finite-stage) capacitance matbernatical model. The effluent concentration profile from two consolidated cores exhibited corisidera ble asymmetry, while two unconsolidated cores yielded nearly symmetrical profiies. All runs resulted in brea~tbrough of the SO per cent concerztratios ignificantly before one pore volume was injected In addition, velocity appreciably afiected the efiluent concentration profile irom a Torpedo sandstone core. The differential capacitance model matched the data significantly better than a simple diffusion 'modeL The capacitance model allows det erminat ion o{ the amount oi dead-end pore space in a porous matrix and tbe eifect of velocity on the rate oi diifusion into tb is SP ace. An experimental program yielding insight into the physical validity oi the capacitance eifect is described.

A review of model applications for structured soils: a) Water flow and tracer transport

“…1d) assumes that the soil micropore network is poorly connected and of such a low permeability that water is immobile in the vertical direction. The MIM approach was originally developed for simulation of fluid displacement in fractured petroleum reservoirs (Warren and Root, 1963;Coats and Smith, 1964). 2D or 3D (g.-j.…”

Overview of inert tracer experiments in key belgian soil types: Relation between transport and soil morphological and hydraulic properties

“…If molecular diffusion drives lateral solute mixing, e.g., lateral mixing within a pore [Taylor, 1953] and diffusion into dead-end pores [Coats and Smith, 1964], the mixing time does not depend on the flow velocity, so that D• • v 2 [Passioura, 1971]. If lateral mixing is driven by advection rather than diffusion, the solute mixing time is inversely proportional to the average flow rate, t* = l*/v with l* a characteristic pore length [Skopp and Gardner, 1992].…”

Lateral solute mixing processes — A key for understanding field-scale transport of water and solutes

“…The trust in these equations and corresponding parameter values was founded on the outcomes of laboratory studies with packed homogeneous soil columns in which the Darcy flow and Taylor dispersion (Taylor, 1953) describe the transport regime. Systematic deviations from the expected transport behavior in less homogeneous porous materials (Coats and Smith, 1964), in undisturbed soil columns (Kissel et al, 1973;Cassel et al, 1975;van Genuchten and Wierenga, 1977) and in field soils (Wild and Babiker, 1976) was the inducement for various refinements of the advectiondispersion equation. Field-scale solute transport experiments carried out during the last ten years have shown that the Richards-and the advection-dispersion equation may be valid in some cases and fail in many others (Jury and Flühler, 1992).…”