PREDICTING SOLUTE TRANSPORT IN HETEROGENEOUS MEDIA FROM RESULTS OBTAINED IN HOMOGENEOUS ONES - AN EXPERIMENTAL APPROACH

The aim of this paper is to show that the hydrodispersive transport pa rameters of a solute in a heterogeneous medium can be predicted using parameters determined by several experiments with the different homoge neous media that constitute together the heterogeneous one. Elementary rules for predicting these parameters are defined. Three types of exp eriments were carried out. (1) Homogeneous medium transport experiment s in 1-D columns. They were fitted with the help of a new numerical pa rticle tracking method, including advection-dispersion and exchange be tween mobile and immobile water with first-order kinetics. (2) Layered heterogeneous media. The experiments were simulated by the numerical model without fitting, using the parameters of each of the layers of t he homogeneous media included in the heterogeneous one. The results pr ove that, in such layered media, the global transport problem can be c onsidered as the convolution of elementary transports in homogeneous b locks. We will therefore conclude that the reservoir simulation method s which represent the heterogeneous reservoir as a random set of eleme ntary homogeneous blocks can be used to represent transport if each el ementary block is given its appropriate hydrodispersive parameters. (3 ) Homogeneous mixtures of two pure components. The experiments produce d three interesting results. The immobile water volume is the direct l inear combination of its equivalent in the two components, weighted by the volumetric fraction of the component in the mixture. The dispersi vity of the medium also evolves linearly, but is affected by an initia l sharp rise due to a strong increase in local flow path heterogeneiti es whenever a ''foreign body'' is introduced into a pure component. Th e exchange rate between mobile and immobile water is also perturbed by mixing. In a binary mixture of one component with dual porosity and a nother one without, the exchange rate decreases with the increase of t he volumetric fraction of the medium without dual porosity. It seems t hat, even if it does not modify the volumes of immobile and mobile wat er, it reduces the surface/volume ratio of the solid medium and conseq uently the exchange rate. Mixing rules could be adopted in order to mo dify the values of the hydrodispersive parameters that need to be intr oduced for the elementary blocks of heterogeneous reservoirs. (C) 1997 Elsevier Science B.V.