The present invention relates to a method for determining at least one combined proportion cube. For each one of a plurality of facies, the determination involves receiving a reference proportion cube, said reference proportion cube having a first average proportion, and receiving an auxiliary proportion cube. Furthermore, for at least one of a plurality of facies, the determination comprises the modification of the auxiliary proportion cube, wherein the modified auxiliary proportion cube has a second average proportion, and the second average proportion is at a distance that is lower than a predetermined distance of the first average proportion and the combination of said reference proportion cube and said modified auxiliary proportion cube.