Digital rock analysis systems and methods with multiphase flow REV determination
The pore structure of rocks and other materials can be determined through microscopy and subject to digital simulation to determine the properties of multiphase fluid flows through the material. To conserve computational resources, the simulations are preferably performed on a representative elementary volume (REV). The determination of a multiphase REV can be determined, in some method embodiments, by deriving a porosity-related parameter from a pore-matrix model of the material; determining a multiphase distribution within the material's pores; partitioning the pore-matrix model into multiple phase-matrix models; and deriving the porosity-related parameter from each phase-matrix model. The parameter's dependence on phase and saturation can then be determined and analyzed to select an appropriate REV size.
1. A digital rock analysis method that comprises:
deriving from a pore-matrix model at least one pore structure parameter;
determining a distribution of multiple phases within pores of the pore-matrix model;
based on said distribution, partitioning the pore-matrix model into multiple phase-matrix models;
deriving said at least one pore structure parameter from each of the phase-matrix models; and
producing a representation of the at least one pore structure parameter's dependence on said distribution.
2. The method of claim 1 , wherein the at least one pore structure parameter comprises:
a distribution of standard deviation of subvolume porosity and a distribution of standard deviation of subvolume pore surface-to-volume ratio.
3. The method of claim 2 , further comprising adjusting a subvolume length scale until moments of said distributions of standard deviation converge to indicate a representative elementary volume (REV) size.
4. The method of claim 1 , further comprising converting one or more images of a sample into said pore-matrix model.
5. The method of claim 4 , further comprising acquiring said one or more images with a scanning microscope.
6. The method of claim 1 , wherein said multiple phases comprise a wetting fluid and a non-wetting fluid.
7. The method of claim 1 , wherein said determining a distribution comprises simulating invasion by a non-wetting fluid phase.
8. The method of claim 1 , wherein the representation is a graph showing a dependence of a distribution of standard deviation of subvolume porosity on saturation.
9. The method of claim 1 , further comprising displaying said representation to a user.
10. The method of claim 1 , further comprising comparing said representation for a full pore-matrix model to said representation for a portion of the pore-matrix model to find a multiphase representative elementary volume (REV).
11. A digital rock analysis system that comprises:
a memory having software; and
one or more processors coupled to the memory to execute the software, the software causing the one or more processors to:
derive from a pore-matrix model at least one pore structure parameter;
determine a distribution of multiple phases within pores of the pore matrix model;
based on said distribution, partition the pore-matrix model into multiple phase-matrix models;
derive from each phase-matrix model said at least one pore structure parameter; and
produce a representation of the at least one pore structure parameter's dependence on said distribution.
12. The system of claim 11 , wherein the at least one pore structure parameter comprises: a distribution of standard deviation of subvolume porosity and a distribution of standard deviation of subvolume pore surface-to-volume ratio.
13. The system of claim 12 , wherein the software further causes the one or more processors to adjust a subvolume length scale until moments of said distributions of standard deviation converge to indicate a multiphase representative elementary volume (REV) size.
14. The system of claim 11 , wherein the software further causes the one or more processors to convert one or more images of a sample into said pore-matrix model.
15. The system of claim 14 , wherein the software further causes the one or more processors to acquire said one or more images with a scanning microscope.
16. The system of claim 11 , wherein said multiple phases comprise a wetting fluid and a non-wetting fluid.
17. The system of claim 11 , wherein as part of said determining a distribution the software causes the one or more processors to simulate invasion by a non-wetting fluid phase.
18. The system of claim 11 , wherein the representation is a graph showing a dependence of a distribution of standard deviation of subvolume porosity on saturation.
19. The system of claim 11 , wherein the software further causes the one or more processors to display said representation to a user.
20. The system of claim 11 , wherein the software further causes the one or more processors to compare said representation for a full pore-matrix model to said representation for a portion of the pore-matrix model to find a multiphase representative elementary volume (REV).