Abstract: The invention concerns a method for building a three-dimensional (3D) cellular partition covering a 3D geological domain by defining the cells of the partition, characterized in that said method comprises the following steps A “3D screen construction step” for constructing a 3D screen which is a 3D elementary partition covering the geological domain, said 3D screen being composed of a plurality of voxels (Vi) which are elementary volume elements, A “voxel painting step” for associating a cell identifier (Cell-id) to each voxel, A “cell definition step” for defining the cells of the geological domain, each cell of the geological domain being defined as the subset of voxels of the 3D screen associated to the same cell identifier, thereby allowing the definition of the cells of the geological domain without having to code the geometry and/or topology of said cells in said geological volume.