This paper presents a new model and its solution for the flow of tracers in reservoirs, both radioactive and chemical, under constant mass flux conditions, which can be used for the design, evaluation and interpretation of injection tests. The models developed consider homogeneous and naturally fractured reservoirs (NFR). For the case of NFR, a transient fracture-matrix tracer transfer is assumed. The transient between two porous media is modeled in a convolution form and using a skin form to obtain a pseudosteady state behavior. The models and the solutions acquired include the tracer lost to the matrix inaccessible (dead end) pore volume. The dimensionless groups used in this work resemble as much as possible those used in well test analysis.
Short and long time approximate analytical solutions for these tracer flow conditions are derived, which are useful to validate the general Laplace space solution, and for the interpretation of the tracer response in observation wells.
The solutions presented in this work were applied to real field interwell (observation) tracer responses, allowing the estimation of important fluid and reservoir parameters, such as the radial dispersion coefficient, , and for NFR the average fracture aperture (width) and the block size.
The evaluation and interpretation of a pulse tracer test in a complex naturally fractured and stratified carbonate reservoir, is evaluated and analyzed. In this test a chemical tracer Perfluoromethylcyclopentane (PMCP) was used.

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