Method of modelling a subsurface volume

1. A method of modelling a subsurface volume for at least one of surveillance, monitoring, optimization, and prediction of hydrocarbon reservoir and well systems, the method comprising:

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 of the subsurface volume;

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 peripheral 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 cell adjacent to said peripheral sub-cell;

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's component sub-cells;

constructing a model of the subsurface volume based on the one or more low order property values; and

wherein the method mitigates bias associated with assumption of facies boundaries.

2. The method as claimed in claim 1 wherein the step of attributing one or more low order property values in accordance with the high order property attributed to the adjacent cell, 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, comprises:

attributing the low order property value to each of these peripheral sub-cells according to the determined low order value for a particular cell, attributed with the high order property of the adjacent cell.

3. The method as claimed in claim 1 wherein the step of attributing one or more low order property values in accordance with the high order property attributed to the adjacent cell, 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, comprises:

attributing the low order property value attributed to the corresponding adjacent cell, or to a sub-cell comprised within the corresponding adjacent cell, to each of these peripheral sub-cells.

4. The method as claimed in claim 1 , wherein the step of dividing each cell comprises:

defining a cell centre of the cell;

determining, for each cell face of the cell, a volume delineated by edges connecting each of vertices of each cell face to the cell centre; and

defining an intermediate face dividing each of said volumes into a volume adjacent the cell centre thereby forming one of said central sub-cells and a volume adjacent the cell face thereby forming one of said peripheral sub-cells.

5. The method as claimed in claim 4 wherein said cell centre is located at a barycentre of the cell and the intermediate face is located at a mid-Euclidian distance between the cell face and the cell barycentre.

6. The method as claimed in claim 1 , wherein the grid comprises regular shaped cells, and the step of dividing each cell is performed on only one cell, the remaining regular cells being divided according to sub-cell dimensions of said only one cell.

7. The method as claimed in claim 1 , wherein the step of 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's component sub-cells, comprises averaging the one or more low order property values attributed to each of the sub-cells comprised within the cell, weighted in accordance with relative volumes of each of the sub-cells comprised within the cell.

8. The method as claimed in claim 7 wherein the step of 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's component sub-cells, comprises transforming the one or more original low order property values attributed to each cell's component sub-cells such that they are defined in terms of scalable properties, performing said averaging and reverse transforming the averaged one or more low order scalable property values such that they are defined in terms of the original low order properties.

9. The method as claimed in claim 1 , wherein processing of the high order properties and low order properties is performed in parallel.

10. The method as claimed in claim 1 , further comprising the step of using results of said method to aid hydrocarbon recovery from a reservoir.

11. A computer-program product comprising a non-transitory computer-usable medium having computer-readable program code embodied therein, the computer-readable program code adapted to be executed to implement the improved method as claimed in claim 1 .