Method of characterising a subsurface volume

1. A method of characterizing a subsurface discretized volume comprising a plurality of cells, the method comprising extracting a geobody from seismic data arranged within the discretized volume, the geobody comprising a subset of the plurality of cells, each cell of the subset having one or more properties indicative of a particular fluid phase, wherein the extracting comprises:

determining a propagation probability value for each cell indicative of the probability that a front propagates through the cell;

beginning from a source within the discretized volume, using the propagation probability value to calculate a traveltime for each cell, the traveltime describing the time the front takes to travel from the source point to the cell;

using the traveltimes to extract the one or more properties indicative of a particular fluid phase of the geobody from the seismic data; and

using the extracted one or more properties indicative of a particular fluid phase of the geobody to aid hydrocarbon recovery from a reservoir comprising the discretized volume by:

monitoring whether the volume and geometry of the geobody corresponds to a planned geobody volume and planned geometry relating to a volume of an injection fluid injected during the hydrocarbon recovery; and

modifying an injection strategy used in the hydrocarbon recovery if the geometry of the geobody does not correspond to the planned volume and geometry, wherein the modifying the injection strategy includes at least one of modifying where the injection fluid is injected, the injection fluid used, the temperature of the injection fluid, and the pressure of the injection fluid.

2. The method as claimed in claim 1 wherein the propagation probability value is used as a velocity or slowness for the front when calculating the traveltimes.

3. The method as claimed in claim 1 wherein a boundary of the geobody is defined by cells all having a single traveltime attributed thereto.

4. The method as claimed in claim 3 wherein the single traveltime is determined from the planned geobody volume.

5. The method as claimed in claim 4 wherein the planned geobody volume is based upon the volume of the injection fluid injected during hydrocarbon recovery.

6. The method as claimed in claim 4 , wherein the planned geobody volume is based upon a known porous volume within the discretized volume.

7. The method as claimed in claim 1 wherein using the traveltimes to extract the geobody comprises:

sorting the cells in accordance with their traveltime; and

beginning with the cells having a shortest traveltime, cumulating a product of a cell volume and a cell volume fraction property until a target geobody volume is reached.

8. The method as claimed in claim 1 , wherein the step of determining the propagation probability value for each cell comprises using a transfer function to transform an indicator property value indicative of the probability that a cell is included within the geobody.

9. The method as claimed in claim 8 wherein the transfer function is used to transform a plurality of combined indicator property values, each indicative of the probability that a cell is included within the geobody.

10. The method as claimed in claim 8 wherein the propagation probability value is anisotropic, the transfer function accounting for the anisotropy of the propagation of the front.

11. The method as claimed in claim 1 , wherein the method uses a fast marching method to determine the propagation of the front.

12. The method as claimed in claim 1 , wherein the discretized volume comprises one or more second sources in addition to said source and the traveltime describes a minimum time the front takes to travel to a cell from any source point to the cell.

13. The method as claimed in claim 1 , wherein the source comprises one or more of a perforation, well and fluid contact.

14. A computer program comprising computer readable instructions which, when run on suitable computer apparatus, cause the computer apparatus to perform the method of claim 1 .

15. A non-transitory computer program carrier comprising the computer program of claim 14 .

16. An apparatus specifically adapted to carry out the steps of the method as claimed in claim 1 .