EFFICIENCY OF MISCIBLE DISPLACEMENT IN FRACTURED POROUS MEDIA

During the injection of fluids that are miscible with oil for enhanced oil recovery, oil recovery and transport of the injectant are controlled by fracture and matrix properties in naturally fractured reservoirs (NFR). For such systems, the transfer between matrix and fracture due to diffusion is the main oil recovery mechanism. Similar processes can be encountered during the sequestration of greenhouse gases, and transport of contaminants in subsurface reservoirs. Understanding the effects of the parameters on the dynamics of the process is essential in modeling such processes. In fact, the description of matrix fracture interaction for dual porosity dual permeability models developed for NFRs is still a challenge.

Experiments were performed to study the process of diffusion during flow in fracture. Berea sandstone and Indiana limestone samples were cut cylindrically in different diameters and lengths. An artificial fracture spanning between injection and production ends was created and the sample was coated with heat shrinkable teflon tube. Different solvents (heptane, kerosene, and IPA) were injected from one end of the core at a constant rate at different injection rates. Oil recoveries were correlated to the injection rate for different matrix sizes, wettabilities, permeabilities, orientations, oil types, amounts of water in matrix and oil solvent diffusion coefficients. A critical rate that maximizes the oil recovery while minimizing the amount of the injected fluid was defined. Then, the ratio of matrix recovery to solvent injected was correlated to the newly defined dimensionless group (fracture diffusion index, FDI). The FDI is the ratio of fracture flow parameters (viscous forces) to matrix diffusion parameters.

It is expected that the experimental results and the dimensionless group, FDI, will be useful in deriving matrix fracture transfer function for diffusion that is controlled by the flow rate, matrix and fluid properties.