Mathematical modeling of tracer behavior in short‐term experiments in fissured rocks

Transport equations for a single fissure in a porous matrix are coupled with a chemical model allowing for both an instantaneous equilibrium governed by a linear adsorption isotherm and a nonequilibrium kinetic reaction of the first order. The fitting procedure of the obtained solution is improved by additional fitting of the mass recovery curves; i.e., the fitting consists of a trial-and-error procedure applied in turn to the concentration tracer curve and the mass recovery curve until a given set of parameters gives the best fit of both theoretical curves to the experimental data. The model is tested against known multitracer experimental data from a fissured chalk formation. It is shown how some physical parameters can be obtained by a combined interpretation of the tracer and pumping data. However, in the case of adsorbable tracers some of the parameters must be known from a nonsorbable tracer experiment. In spite of its approximate nature the model works surprisingly well for nonsorbable tracers and reasonably well for sorbable solutes.