1. A method for determining a karstic region modified by karstification phenomena, comprising: a/ receiving a geological model of the karstic region comprising cells, said model comprising at least one seed zone comprising cells of the model and at least one target zone comprising cells of the model, each cells of the model having coordinates; b/ determining a seed cell in the cells of the at least one seed zone; c/ determining a target cell in the cells of the at least one target zone; d/ if a distance between the seed cell and the target cell is above a predetermined distance: d1/ determining a bifurcation zone based at least on the coordinates of the seed cell, the coordinates of the target cell, a distance distribution, and an angular distribution, d2/ determining a bifurcation cell in said bifurcation zone; d3/ re-iterating step d/ with a cell based on said bifurcation cell as the seed cell; e/ determining trajectory cells in the geological model based on the seed cell, the target cell and bifurcation cells determined in step d/; and f/ for each current cells in the trajectory cells, f1/ determining conduits characteristics based on a predetermined conduit density distribution, a predetermined conduit aperture distribution and trajectory cells connected to said current cell; f2/ determining cell characteristics based on the conduits characteristics of said current cell.