The Use Of Flue Gas With Steam In Bitumen Recovery From Oil Sands

Abstract

Experimental results for bitumen recovery from oil sands by continuous and cyclic injection of several steam-flue gas combinations are presented in this paper. Steam, steam-CO2, steam-N2 and steam-CO2-N2 mixtures were injected (3.55 MPa and 100% steam quality into an oil sand test bed which contained a high permeability communications path between injection and production wells. The concentrations of flue gas (N2 + CO2) and carbon dioxide in steam were designed to simulate those which would be produced from a "down-hole " steam generator which uses either air or oxygen. The test results show that the addition of flue gas to steam substantially improves both rate and ultimate recovery of bitumen as compared to that obtained by steam-alone. The steam-CO2 mixture was superior to either steam-N2 or the steam-flue gas combinations. Introduction Oil sand is a complex mixture which contains mineral matter (primarily quartz and feldspar), organic materials (bitumen), gases and water with bitumen and water saturations up to 15% and 2% by weight, respectively. The oil sand has a permeability of about 3.0 µm2 and a porosity of about 32%. The viscosity of bitumen varies considerably and in some cases reaches values about 1000.0 Pa.s at reservoir conditions (15 °C). The technology of exploiting the oil sand deposits by surface mining has been proven in the last few years. However, the available oil sand resource which is surface-mineable accounts for only about 10% of the total available deposit, with the remaining 90% uneconomically mineable due to excessive overburden depth. For the deeper portions of the oil sand deposits, the technology of in-situ extraction has received considerable interest during recent years. In general, in-situ methods involve some means of reducing the viscosity of and then displacing bitumen to a production well. Injection of a hot fluid into the oil sands (most commonly steam) is normally used. Addition of solvents, gases or solvent-gas combinations may also be used in conjunction with steam. Two methods of steam injection have been employed: single well steam stimulation and steam drive. In this paper, the primary focus will be on the steam drive process. At reservoir conditions, most commonly, the first step in a steam drive process is establishment of communication between injection and production wells. Thereafter, the recovery process comprises of channeling of the steam, heating of the adjacent oil layer(s) by conduction and displacement of the heated oil by an entrainment process(1) in which healed oil is displaced toward the producing well by flowing steam and condensed water. Interaction between fluids flowing in the communication path and the surrounding formation is a very important part of the recovery process. There appears to be a dynamic balance between the rate of heat transfer from the steam zone to the adjacent oil layers and the flow displacement processes in the interface region between the steam zone and the oil zone. This balance can result in the occurrence of an optimum injection rate.

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