The invention relates to a method having applications for oil exploration and CO.sub.2 storage of determining the three-dimensional distribution of the absolute permeability of a heterogeneous sample. The method includes: determining a 3D porosity map of the sample; carrying out a viscous miscible displacement experiment during which the evolution of the differential pressure on either side of the sample is determined; from this evolution, determining a 1D absolute permeability profile along the sample and constructing a first 3D permeability map from the 3D porosity map; estimating a simulated differential pressure by simulating numerically a viscous miscible test from the first permeability map and from the 1D permeability profile; determining the three-dimensional distribution of the absolute permeability of the sample by modifying at least once the first permeability map so as to minimize the difference between the simulated differential pressure and the differential pressure measured over the course of time.