The method for identification of residual oil from the data of flow of two tracers with different solubility in oil is developed for fractured-porous reservoirs.

The solubility of tracer in the immobile phase (oil, retrograde condensate) leads the lag of the tracer front propagation behind the displacement front. The ratio of the tracer front velocity and the velocity of total flux is determined by the saturation of immobile phase. It allows us to determine the saturation of the residual hydrocarbon phase from the data of flow of two tracers with the different magnitude of the constant of tracer distribution between the water (gas) and oil (condensate).

A new equations for flow of two tracers in fractured-porous media are derived. Both diffusive and convective mechanisms of the tracer mass transfer between blocks and fractures are taken into account. The hydraulic interaction between fluxes in cracks and in matrix is described as well. Problem of one-dimensional flow leads to the linear system of hyperbolic equations. Analytical solution for ID problem of injection of water (gas) with the two tracers is obtained. Results of theoretical prediction of tracers wave propagation are in a good agreement with the data of laboratory experiments.

Exact explicit formulae for propagation of the concentration wave of two tracers allows us to solve an inverse problem. Method for improved characterization of fractured-porous media from data of two tracers concentrations on the exit of reservoir is developed. Measurement of the first tracer concentration allows us to determine the following properties of fractured-porous media: fractional flow function (fraction of the flux via fractures in the total flux); fraction of porous space of cracks in the total space of fractured-porous media; coefficient of mass transfer between fractures and matrix. Information about the concentration of the second tracer permits us to determine the saturation of the immobile phase separately in fractures and in blocks.

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