Performance Evaluation of Solvent Assisted-Steam Injection Processes with Asphaltene Insoluble Solvents
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Date
2016-05-06
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Abstract
Adding solvents to steam flooding processes during bitumen production can reduce the water and natural gas usage but may create a new unique set of problems. Most solvents are toxic and are prohibited to be used on sites. Most importantly, since the solvent-bitumen-steam interactions are not well understood, solvent-steam coinjection into bitumen reservoirs may lead to produce lower quality oil. Because of the high asphaltene content of bitumen reservoirs and the presence of clays in the reservoir, the quality of the produced oil is determined mainly by the interaction of solvents with these elements. These interactions can be detrimental on the performance of the steam processes by enhancing the asphaltene precipitation which can plug the reservoir pores and/or by forming emulsions in produced oil which may require additional surface facilities to separate water-in-oil emulsions at the surface due to asphaltene-water interactions. This study will investigate the solvent-asphaltene-clay-steam interactions that occur during solvent-steam injection into high asphaltene content bitumen reservoirs.
Two solvents were used: n-hexane (E1 and E4) and a commercial solvent (CS) (E2 and E5). Five experiments were run: two miscible floodings (E1 and E2), one steam flooding (E3) and two SA-SF (E4 and E5). The performances of the solvents were evaluated according to the oil production and the produced oil quality, the asphaltene clay content, viscosity and emulsions of this oil.
During miscible flooding, E1 (n-hexane flooding) performed only slightly better than E2 (commercial solvent flooding). The quality of produced oil, however, was vastly different due to the asphaltene and clay content. The commercial solvent is composed of heavy dearomatized hydrocarbons ranging from C11 to C16, and therefore is more prone to carrying asphaltenes. During E3, E4, and E5, in which steam was used, the differences were made even clearer. Although E5 had a better recovery than steam alone (E3), the oil quality was very poor, containing high amounts of asphaltene and clay. However, for E4 where steam and n-C6 were injected more clay was observed than E5 in which steam and commercial solvent (CS) were injected. E5 also produced less oil than E4; the heavier weight of the CS keeps it at a liquid state even at steam temperatures, limiting its coverage of the rock. The high asphaltene content of the produced oil also caused severe emulsions problems, as the asphaltene and clays present deposited in the water oil interface and stabilized the water droplets.
From these results, the use of heavy hydrocarbon solvents is not recommended for SA-SF processes into high asphaltene content reservoirs, as their interactions with the bitumen, reservoir and steam are detrimental to not only the recovery factor, but also the quality of the oil.
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solvent, steam, Asphaltenes, clays, Bitumen