An earlier account of gravity segregation (Rose and Passioura 1971a) contained a substantial error (that of an incorrect frame of reference for flow) and several printing mistakes (the results of a 7-week postal strike in the UK).
Gravity segregation has been extensively studied by petroleum engineers (e.
We start by recalling the theory of gravity segregation of immiscible fluids and then compare this theory with the outcome of published experiments on miscible liquids.
mu]][theta][upsilon]L is defined as the gravity segregation number.
We estimated the values of the gravity segregation number, [beta] (Eqn 8), in the following way.
We assume that the simultaneous flow of water and solutes through a pomus material during miscible displacement accompanied by gravity segregation may be described by the convection--diffusion equation (CDE), Eqn 11 of van Genuchten and Wierenga (1986):
This observation appears counterintuitive: one might expect that mixing about the displacing front would lead to an earlier start and a later end to breakthrough in miscible than in immiscible displacements, However, Kumar and Kimbler (1970) concluded, from 5 displacements in a 3-dimensional radial model constructed from an artificial consolidated sandstone, that mixing has a retarding effect on gravity segregation in miscible liquids.
Figure 4 shows stages in the development of miscible displacement accompanied by gravity segregation in photographs of 0.
This happens because the increase in hydrodynamic dispersion as the speed of displacement increases outweighs the corresponding decrease in gravity segregation and illustrates the complex interaction between dispersion and segregation in miscible displacements.
At the lowest speed during horizontal flow, gravity segregation dominates and results in a dispersed BTC because of greater mixing due to the shallow gradient of the tilted interface between the 2 liquids; during vertical displacement, the BTC is steep because of little hydrodynamic dispersion about the stable interface between the liquids.
through sepiolite, was also due to gravity segregation.
We have explored in detail some consequences of gravity segregation during miscible displacement, a phenomenon that occurs when saline groundwater intrudes into coastal aquifers, an increasingly common problem worldwide.