Enhanced recovery of conventional crude oils with flue gas

Abstract

Flue gas injection is becoming more attractive as a feasible and environmentally friendly process for improving oil recovery from conventional oil reservoirs. When obtained from surface sources, the flue gas process has an added advantage of reducing carbon dioxide (CO2), a greenhouse gas, from being vented into the atmosphere. Flue gas can also be generated in situ by the spontaneous ignition of oil when air, a readily available gas, is injected into high temperature, high pressure conventional oil reservoirs. The availability of flue gas and/or air and the observed high oil recovery potential make the flue gas process an economically attractive process. The oil recovery potential from conventional oil reservoirs by flue gas injection, the displacement mechanism, and the effect of oil composition on these parameters were studied in the laboratory with three flue gas compositions having 0%, 16%, and 30% CO2 content and two recombined conventional crude oils (oils A and B) obtained from two different reservoirs. The oils were displaced by the flue gases in a 2.44 m (8 ft.) long, 5.1 cm (2 in.) diameter Berea sandstone core at irreducible brine saturation as well as in a 18.288m (60 ft.) long slim tube. These studies were conducted at reservoir pressures ranging from 17.62 MPa to 41.58 MPa and temperatures of 116°C and 80.6°C, corresponding to the respective reservoir temperature of the oils studied. Experimental coreflood results show that oil A recovery increases from 32.95% to 41.00% of the initial oil in place (IOIP) at 27.7 MPa as the CO2 content in the flue gas increases from 0% to 30%. The recovery also increase with pressure from 32.95% to 50.94% IOIP at 0% CO2 flue gas content as the displacement pressure increases from 27.47 MPa to 41.58 MPa. Oil B recovery also increased from 45% to 50% IOIP with increase in CO2 content in flue gas from 16% to 30% at 17. 7 MPa. The results also show that conventional oil will benefit from enriched flue gas injection. Based on coreflood simulations using CMG-GEM simulator, maximum oil was recovered at 80% CO2 for oil A and at 60% CO2 for oil B at 68.95 MPa. Both oils were displaced under a combined vapourizing-condensing mechanism, which was enhanced with CO2 enrichment.