PHASE-BEHAVIOR AND SCALED MODEL STUDIES OF PROTOTYPE SASKATCHEWAN HEAVY OILS WITH CARBON-DIOXIDE

Non-thermal enhanced oil recovery (EOR) techniques show good potential for recovering oils from the thin and shaly heavy oil reservoirs of S askatchewan. Among the non-thermal processes, immiscible carbon dioxid e injection holds the most promise of accessing these reservoirs. This technique, however, is much less developed than thermal methods. The process, if proven applicable to Saskatchewan reservoirs between three and seven metres thick, will access approximately 90% of the total oi l-inplace. Considering the above, a multiclient experimental research program was initiated at the Saskatchewan Research Council. The object ive of this research program is to evaluate various solvents in the co ntext of the heavy oil resource and to investigate displacement mechan isms associated with immiscible gas injection processes. This paper is divided into two sections. The first deals with the characterization of a Kindersley area heavy oil. The characterization includes analysis of stock-tank oil with and without additives, recombined reservoir fl uid, and reservoir fluid plus carbon dioxide. The second section descr ibes a scaled physical model and two displacement experiments conducte d using a Lloydminster area heavy oil. The laboratory phase behaviour data were generated to show the effect of pressure and temperature on carbon dioxide solubility, oil density and viscosity, compressibility, and swelling factors. The addition of 73.1 sm(3)/m(3) of carbon dioxi de at 7 MPa reduced the viscosity of the reservoir fluid at 25.5 degre es C from 819 mPa.s to 45 mPa.s, an eighteen-fold reduction. The same reduction in viscosity by thermal methods would require heating the sa mple to approximately 80 degrees C. The above oil, under similar condi tions, increased in density from 963.0 kg/m(3) to 974.3 kg/m(3) and sw elled approximately 15%. Two scaled model experiments (secondary displ acements) were conducted using a 10-cycle water-alternating-gas (WAG) process with a WAG ratio of 4:1. In each run, the total mass of carbon dioxide injected was 1.41 g.mole (0.53 PV at 2.5 MPa, 0.30 PV at 4.1 MPa). These displacements indicated the immiscible carbon dioxide WAG process to be partially sensitive to the operating pressure in the ran ge of study. More important is the relative volume of carbon dioxide, at experimental conditions, which dictates overall performance.