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Water is the most predominant component in steam injection processes, such as steam-assisted gravity drainage (SAGD). The main hypothesis in this research is that in-situ oil transport can be substantially enhanced by generating oil-in-water emulsion, where the water-continuous phase acts as an effective oil carrier. The objective of this paper is to evaluate the capability of oil-in-water emulsions to transport bitumen in porous media within a temperature range of 350 – 470 K at 3.5 bar.
Athabasca bitumen and two organic alkalis of different chemical structures were used in this research. An alkali concentration of 0.5 wt% was found optimal to form oil-in-water emulsions with bitumen and NaCl brine at a range of salinity. In-line density measurements were conducted to confirm that there was single-phase emulsion in a 200-ml accumulator. Then, flow experiments through glass beads packs were carried out to estimate effective viscosities of oil-in-water emulsions at typical shear rates in oil sands under SAGD (e.g., 1 to 10 [1/sec]). The bitumen concentration in each emulsion sample was quantified directly by using an emulsion breaker. Finally, emulsion molar flow rates were calculated with an analytical equation of gravity drainage.
Emulsion viscosity measurements showed shear-thinning behavior with much lower viscosity than the original bitumen. At an estimated shear rate of 1.0 per second, for example, the viscosity of oil-in-water emulsion for 0.5 wt% alkali was 12 cp at 350 K, which is much lower than the original bitumen viscosity, 190 cp, at the same temperature.
The obtained experimental data, such as effective emulsion viscosity, bitumen content in emulsion, and properties of the porous media used, were then used to quantify the bitumen molar flow under gravity drainage. Results showed that oil-in-water emulsion can enhance in-situ bitumen transport by a factor of 4 in comparison with SAGD, and by a factor of 2 in comparison with hexane-SAGD.
This research demonstrate that the clear advantage of bitumen transport via water-external emulsion can be obtained by adding only 0.5 wt% of alkali in brine. The mobility of the bitumen-containing phase is substantially enhanced because the oil-in-water emulsion flows as a single phase with a much lower viscosity. In contrast, conventional solvents, such as n-alkane mixtures, reduce bitumen viscosity by dilution using a substantial amount of those expensive solvents.
A difference between the two alkalis used is in their ability to dissociate in water; one of the alkalis has three more dissociation sites than the other. This led to different phase behaviors and rheological properties observed in our experiments.
This is the first time the potential of organic alkalis to improve bitumen transport is quantified experimentally. The experiments were newly designed to evaluate the molar flow rate of oil-in-water emulsions at SAGD operating conditions. The alkaline concentration required for effective bitumen transport is even lower than 1 wt% in the brine. Recovery mechanisms of alkali-SAGD are explained in detail, and compared to the flow characteristics in SAGD and other solvent-assisted SAGD.
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