The potential benefits of using a surfactant with steam to recover viscous oil are now well recognized. This study describes a series of laboratory displacement runs carried out using Cold Lake and Athabasca oil sand cores, the steam was injected into a high permeability path emplaced between the injection and production ends of the core. The effects on oil recovery of using surfactant after steam-only depletion including the size, timing and concentration of the surfactant slug, the use of a non-condensible gas and the permeability of the path were investigated. The results are related to theability of the surfactant to temporarily stabilize a foam with either steam or a non-condensible gas phase, The foam acts to divert the steam to the nswept zones of the core, thereby increasing bitumen recovery.
Over the last several years, the use of surfactants (either alone or with a non-condensible gas) in steam recovery processes has attracted a great deal of attention 1–4, However, results of field use have not always been positive, and the mechanisms of action ofthese reagents and the conditions under which they ay best be used are not well understood.
Earlier experiments in this laboratory, using both core-size and large scale test cells packed with Athabasca oil sand, showed a large increase in bitumen displacement efficiency when sulfonate surfactants were used with hot water or steam5–8. During the steam runs in core-sized cells, the nhanced production was accompanied by very high pressure drops across the core. Complimentary experiments on the flow behavior of steam-water mixtures in the presence of surfactant, together withnumerical simulations, implicated steam-foam formation as the mechanism responsible for theenhanced recovery observed in the steam displacement runs7. The steam-foam is thought to block high permeability paths and divert steam to undepleted zones of the core. The ability of surfactants to reduce steam-water relative permeabilities and form steam foams in sand packs has been the subject of a number of recent studies9–13.
In this paper, we describe a number of experiments conducted to further elucidate the process of steam-surfactant recovery from oil sand cores. The rationale for the tests carried out is described below.
If foam blockage of the high permeability path is the mechanism responsible for the improvement inrecoveries, then alternate methods of reducing path permeability in the absence of surfactant should also produce an enhancement in recovery. A run using a low permeability path was carried out to test this hypothesis.
In the earlier steam displacement studies, surfactant was injected with steam continuously throughout therun. It seemed desirable to examine the displacement performance of surfactant when injected after steam-only epletion. There was a concern that steam depletion could in some way alter the core to make the remaining bitumen inaccessible to surfactant enhanced recovery.
Our earlier studies had used laboratory prepared packs of Athabasca oil sand, and there was some question as to whether the results accuratelyreflected what would happen if field cores had been used -it could be argued that the packing procedure introduced experimental artifacts.
