disclosed is a method of modelling a subsurface volume . the method comprises : discretising said subsurface volume to define a grid comprising an array of cells , each cell being defined by cell faces , each cell having attributed thereto one or more high order properties ; dividing each cell into a plurality of sub - cells , said plurality of sub - cells comprising : a plurality of central sub - cells adjacent a centre of the cell , and a plurality of peripheral sub - cells , each adjacent a corresponding cell face ; for each of said central sub - cells , and for each of said peripheral sub - cells for which the cell adjacent to that peripheral sub - cell has attributed thereto the same one or more high order properties as that of the cell in which said peripheral sub - cell is comprised , attributing one or more low order property values in accordance with the high order property attributed to the cell in which said peri - pheral sub - cell is comprised ; for each of said peripheral sub - cells for which the cell adjacent to that peripheral sub - cell has attributed thereto a different one or more high order properties than that of the cell in which said peripheral sub - cell is comprised , attributing one or more low order property values in accordance with the high order property attributed to the adjacent cell ; and determining one or more low order property values for each cell based on the one or more low order property values attributed to each cell &# 39 ; s component sub - cells .