for th horizontal flow directions a reference analytical solution can also be calculated since the flow geometry is a 2d flow in these directions 3d flow geometry concerns the z direction ______________________________________equivalent fine grid present analyticalpermeabilities md simulation method solution______________________________________kx 0 119 0 120 0 120ky 0 224 0 227 0 226kz 0 255 0 267anisotropy 1 56 1 62kz kxky sup 0 5______________________________________ it is the clear that the results obtained by the disclosed method are very close to the corresponding values obtained with the analytical solution and the fine grid simulation for directions x and y in addition the difference in the vertical equivalent permeability values involving 3d flow remains acceptable hence the anisotropy ratio equal to 1 6 is satisfactorily predicted by the method with a very limited number of cells the method according to the invention which provides easily transposed representation of a natural fracture network is well adapted for fracture flow computations it can also be useful for improving the original image of the fracture network such image is actually obtained form a stochastic fracture generator using as input results of integration of filed fracturing data in a fracture characterization model as shown in the already cited patents fr a 2.