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 better define the residual oil under waterflood and gasflood in these reservoirs. The cell constructed of fused glass beads contains pores of three sizes. The large pores or vugs are connected to each other by intermediate sized worm holes to form a high permeability channel one end to the other. The maximum to minimum pore size ratio is approximately 16. This corresponds to a maximum to minimum permeability ratio of 270.
Two types of experiments were done:
water displacement upward followed by oil displacement downward and,
gas displacement downward.
Laboratory velocities ranged from 1 ft/day to 200 ft/day corresponding to equivalent field velocities ranging from 3.6 ft/year to 700 ft/year. Motion pictures were made of the displacement experiments using time lapse techniques.
The results of the alternate water-oil displacement studies show that:
displacements are stable over the velocity range studies;
complete resaturation of the matrix porosity by oil will occur when the cell is connected in a manner epresentative of field behavior (matrix-connected);
the apparent capillary height of rise is velocity dependent; and
the oil recovery from the vugs during water displacement is a function of velocity.
The results of the downward gas displacement indicate that:
the displacement is dominated by capillarity; and
it is essentially independent of velocity.
The conclusion that the downward oil flood reestablishes the original high oil saturations is valid regardless of the oil recovery during water displacement. The displacement of water by oil occurs first in the vugs or large pores and then in the matrix. The conclusion that the oil recovery from the vugs by waterflooding increases as the velocity increases is in disagreement with results reported by other investigators for distinctly different types of non-homogeneous pore structure. It is, therefore, essential, in selecting [he optimum method of recovery, to consider the specific nature of the non-homogeneous pore structure.
The Rainbow field, discovered in Northwestern Alberta in 1965, presently comprises some 50 separate reel 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 capped by an initial gas cap. The production mechanisms in these reservoirs, whether it be primary depletion or pressure maintenance by gas, solvent, cr water injection, 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.
