Feasibility of Miscible Displacement In Swan Hills Unit No. 1

Abstract

Abstract A two-dimensional, three-phase fully implicit black oil reservoir simulator was modified to approximately predict miscible flood performance for typical cross sections within the Swan Hills Beaverhill Lake A & B pools. The reduction of reservoir residual oil saturation by miscible displacement has the potential to generate a very substantial incremental oil recovery from horizontal miscible flooding as compared to existing waterflood operations. Gravity override of the low-density and low-viscosity solvent limited the portion of 'reservoir contacted by the solvent. However, the injection of water concurrently with the solvent aided in the displacement process. It was observed that waterflooding prior to miscible flooding improved the oil recovery performance. Economic evaluations, based on the simulator performance predictions, indicate that a horizontal miscible displacement scheme is marginally profitable at discount rates which are less than 10 per cent. Introduction THE SWAN HILLS UNIT No. 1 is located in north central Alberta, and is approximately 44,000 acres in areal extent. The productive horizon, a carbonate reservoir, is within the Swan Hills Member of the Beaverhill Lake. A & B Pool. The producing horizon is subdivided into two geological entities, the Light Brown and Dark Brown members. The Light Brown Member which represents the majority of the Unit'sproductive capacity and recoverable reserves, is comprised of a reef build-up and reef platform region, as indicated in Figure 1. A structural cross section within the study area is shown in Figure 2. The B, C, C and D zones, as indicated in the cross section, represent distinct geological divisions within the Light Brown Member. The reef rim regions exhibit continuous uniform pay development and have excellent vertical and horizontal permeability. The reep lagoonal area exhibits a poorerquality pay with lower vertical permeability within non-communicating zones. The gross thickness of the Light Brown Member in the reef build-up area varies from 296 feet in well 4-16-067-10-W5M to 166 feet inwell 10-28-067-10-W5M Net pay averages around 100 feet. Original oil-in-place for the reef build-up for the Swan Hills Unit No.l is estimated to be 1336 MMSTB"'. Waterflood operations, which are currently estimated to yield a 50 per cent(1) ultimate recovery were commenced coincident with production, so that reservoir pressures have been maintained in excess of the 1820-psig bubble point. Production was limited by proration to market demand until 1970. Waterflooding operations, until that time, were confined to a producing area within the west reef rim region. With the advent of improved market conditions, waterflood and production operations have been extended to the east reef build-up and reef platform area within the Unit. Cumulative production from the Unit area was 185 MMSTB to the end of December, 1973. Miscible flooding has the potential to increase oil recovery by improving volumetric displacement efficiency. Residual oil saturations of 34 per cent were Measured(2) after displacing 20 pore volumes of flood water through oil-saturated cores in laboratory displacement tests, Similar experiments, utilizing propane as the displacement agent, resulted in residual oil saturations of approximately 15 per cent(3).