Steady State Two-phase In a Smooth Parallel Fracture

Abstract

Abstract Steady state two-phase (oil-water) flow experiments were conducted in horizontal smooth parallel-plate fractures. The effect of fracture aperture, oil viscosity, injection rate, and injection method on the multiphase flow characteristics were investigated. The experiment data were analyzed using a porous medium approach and an equivalent homogeneous single phase method. The pressure gradients predicted by the latter are consistent with the measured pressure gradients in all the experiments. Contrary to the well-known Romm's relative permeability versus saturation relationship, the experimental data showed that the sum of the relative permeability's is less than one, which is due to the effect of phase interference on the oil-water flow. The effect of phase interference is more significant in the case of well mixed oil water flow than otherwise. The results also indicate that fracture aperture and oil viscosity do not have an significant impact on the relative permeability's of the oil and water in smooth parallel-plate fractures. INTRODUCTION Investigation of fluid flow in porous and fractured media is of practical importance in areas such as the recovery of oil and gas, the isolation and remediation of nuclear and toxic wastes in geological formation, and the exploitation of geothermal energy. In these applications, fluid flow in fractured media is often dominated by the highly permeable pathways provided by rock fractures and joints understanding the mechanics which govern the multiphase flow in fractures will certainly help to improve the energy recovery efficiency and optimize the waste isolation and remediation process. It is well known that the flow of multiphase fluids in a porous medium is generally governed by the saturation of the pore space occupied by the percolating fluids. Pores occupied by one phase are not available for the flow of the other, that is, each phase interferes with the flow of the other. This interference is controlled primarily by the action of capillary forces developed at the contact zones of the fluid phases in the pore canals. The smaller the size of the pores the more significant will be the effect of capillary forces. To quantify the interference between different fluids, relative permeability functions are introduced and defined as, Equation(1) (available in full paper) where k1 is the effective permeability to phase i, k is the absolute permeability of the medium, and kn is the relative permeability to phase i. Numerous experimental studies have shown that the relative permeabilities are strong functions of phase saturation. Similarly, it is expected that phase interference will affect multiphase flow in fractures. The physics of fluid flow in a fracture is different from that in a homogeneous porous medium. Unlike the three dimensional nature of flow in a porous medium, fluid flow in a fracture occurs in a two-dimensional variable aperture plane, and the rate and flow pattern are controlled by the geometry of the fracture and the effective stress change applied on the fracture. One simple approach to study fluid flow in a fracture is to treat the flow as if it were between two smooth parallel plates.