A study was undertaken to characterize the surfactants that stabilize emulsions occurring in enhanced recovery operations of heavy oil in Saskatchewan. Knowledge about the nature of the stabilizing compounds may help improve emulsion treating technologies and, ultimately, recovery operations. Both oil-in-water emulsions, found in steamflood operations, and difficult-to-break water-in-oil emulsions typical of fireflood-produced crudes were included in this investigation.
Fresh emulsions were collected from five thermal projects in Saskatchewan and the produced (free) water phases subjected to ultra filtration using membrane permeation. Following chemical analysis of the raw permeates, three methods were used to extract and/or isolate the dissolved organic matter from the permeates:
water removal by freeze drying or rota-evaporation;
extraction of the acidified permeates with ethyl acetate, followed by removal of the solvent; and
separation by column chromatography into acidic, neutral and basic fractions. The identification of compounds or compound classes in the isolated products was mainly based on C NMR, GC/MS and IR analyses, but other characterization methods were also employed.
The major constituents in all five sample cases were aliphatic carboxylic acids, benzoic acid and derivatives, and phenol and derivates. Differences were observed in the relative proportions of these constituents and these differences could be related to the origin of the material. Fireflood materials tended to be more aromatic, have a higher benzoic acids content, an average-to-low aliphatic carboxylic acids content, and contain only small amounts of phenols. Steamflood materials, on the other hand, tended to be more aliphatic, have a higher aliphatic carboxylic acids content, a moderate-to-low benzoic acids content, and contain high levels of phenols. Some samples fell in between these two extremes. Because the isolated organic materials could not be redissolved in water, their surface active properties and, hence, their possible efficacy as a surfactant could only be measured indirectly using the original raw permeate solutions. Interfacial tension measurements on these solutions were inconclusive.
Much attention is being given in recent years to the mechanics and economics of the recovery and use of heavy oil and bitumen. The sizeable reserves of heavy oil and bitumen in Alberta and Saskatchewan cannot be extracted by conventional means to any significant degree due to the high viscosities of these oils. Improved recovery is, however, possible with enhanced recovery techniques such as steamflooding and In-situ combustion, both of which are presently in use in the field.
The oil recovered using these methods is almost always produced in the form of oil-water emulsions. While in-situ combustion or fireflooding usually produces very stable water-in-oil (w/o) emulsions, both w/o emulsions and stable, reverse, oil-in-water (o/w) emulsions can be formed in steamflooding operations. The stability and persistence of these emulsions are due to the presence of natural or in situ created surfactants, which are partially soluble in both oil and water phases. Surfactant molecules reside at the interfaces between the liquid phases, with a polar portion of the molecule in the water phase and a nonpolar portion of the molecule in the oil phase.