A second analytical step makes use of simple models. The response curves are decomposed in simple functions using a simple mathematical model based on the standard equations for diffusion in porous media.

where

C(x, t) is the tracer concentration as a function of distance and time (Bq/m3); tN is the normalized time;

D1 is the coefficient of dispersion (m2/d); v is the tracer velocity (m/d); x is the distance from the injection point (m);

CREF is the reference tracer concentration (Bq/m3).

Dispersivity may be calculated by multiplying the ratio (D1/vx) by the distance between the injection and production wells. Therefore, the extrapolated curve obtained before may be decomposed in two simple functions using Anduril software to give the curves shown in Fig. 33, where both functions and their sum are shown together with the experimental data.

The following table presents obtained results using Anduril software for the pair of wells CnE241-CnE324.

The decomposition in two curves may be explained by the fact that the tracer follows two different paths in its migration from the injector to the producer, each of them having different permeabilities.