Vertical Immiscible Displacement Experiments In a Non-Homogeneous Flow Cell

Abstract

Abstract Vertical two-phase displacement studies were conducted using a non-homogeneous flow cell in order to determine the reversibility of water-oil displacements in the heterogeneous Rainbow Keg River pools and to provide a better definition of the residual oil under waterflood and gas flood in these reservoirs. The non-homogeneous flow cell was constructed of fused glass beads. The maximum to minimum permeability ratio was approximately 270. The results of a waterflood upward followed by an oil flood downward over field rates of 4 to 700 fr/yr show that:displacements are stable over the velocity range studied;complete resaturation of the matrix porosity by oil will occur when the cell is connected in a manner representative of field behaviour (matrix-connected);the apparent capillary height of rise is velocity dependent; andthe oil recovery from the vugs during water displacement is a function of velocity, with more oil recovered at the higher velocities. The downward displacement of oil by gas indicates that the displacement process is essentially independent of velocity over the velocity range of 2 to 150 jt/yr. Time-lapse motion picture films were made of the displacement Experiments＿ Introduction THE RAINBOW FIELD, discovered in northwestern Alberta in 1965, now comprises some 50 separate reef reservoirs. Production is mainly from the Middle Devonian Keg River Formation, which lies at a depth of about 6000 feet. The larger reefs have high-vertical- relief (up to 600 feet) oil-bearing zones that are usually underlain by an aquifer and sometimes overlain by an initial gas cap. The production mechanisms in these reservoirs, whether it be primary depletion or pressure maintenance by gas, solvent or water inj ection, will therefore be gravity controlled, and drainage will be predominantly in a vertical direction under effective segregation of the phases in the reservoirs. Volumetric efficiencies are consequently very high, and ultimate recoveries are mainly determined by the residual oil saturation left behind by the displacing fluid. Of the various depletion methods, solvent flooding is the most efficient recovery mechanism, with a residual oil saturation of zero to a few per cent＿ Waterflooding, gas flooding and primary depletion are less efficient. Some 30 per cent of the 1150 million STB of original oil-in-place of the Rainbow Keg River reef is currently under solvent flood, and 60 per cent is being waterflooded. The remaining 10 per cent is under primary depletion. The amount of oil under solvent flood is limited by solvent and gas availability. Solvent is separated from the crude oil, and solution gas may be supplemented with gas from other sources. In each of the solvent flood pools, a solvent bank is injected to cover the oil When this solvent bank becomes large enough to provide miscibility for the lifetime of the project, it is then pushed down to displace the oil by injecting lean gas into the crest of the reef.