Selected cationic and amphoteric surfactants were effective in separating oil-in-water emulsions ... more Selected cationic and amphoteric surfactants were effective in separating oil-in-water emulsions representative of produced emulsions expected during a surfactant/polymer (SP) process for enhanced oil recovery. The aqueous phase of the emulsion contained an anionic surfactant blend, alcohol, and partially hydrolyzed polyacrylamide. Brine composition was a suitable mixture of formation brine with brines from the surfactant slug and polymer drive. The crude oil had an American Petroleum Institute (API) gravity of 31°. Bottle tests were conducted at ambient temperature, which is near the reservoir temperature. Conventional non-ionic demulsifier resins and polymeric cationic flocculants were not effective in removing oil from the aqueous phase. The water content of the oil phase was still well above specification upon heating the emulsions to 50-60°C. However, both oil and water phases of acceptable quality were obtained after 6 h of settling upon the addition of 200 ppm of octyltrimethylammonium bromide (C 8 TAB) at ambient temperature. Additionally, a commercial cationic surfactant at the same concentration yielded acceptable results for both phases in 2 h. Optical microscopy showed significant coalescence after only 1 min in the C 8 TAB system as the cationic surfactant reduced electrostatic repulsion among drops and shifted system phase behavior toward the balanced state between hydrophilic and lipophilic effects, actions well-known to reduce emulsion stability. Some amphoteric surfactants, such as cocobetaine, were also effective in separating these emulsions. The amount of cationic surfactant required could be reduced by adding it simultaneously with a non-ionic demulsifier resin. A commercial cationic surfactant was also found to significantly improve separation of emulsions produced during an alkaline/surfactant/polymer (ASP) process.
The procedure proposed by Packer and Rees (J. Colloid Interface Sci. 40 (1972) 206) to interpret ... more The procedure proposed by Packer and Rees (J. Colloid Interface Sci. 40 (1972) 206) to interpret pulsed field gradient spin-echo (PGSE) experiments on emulsions is commonly used to resolve for the distribution of droplet sizes via nuclear magnetic resonance (NMR). Nevertheless, such procedure is based on several assumptions that may restrict its applicability in many practical cases. Among such constrains, (a) the amplitude of the spin-echo (signal) must be influenced solely by the drop phase, and not by the continuous phase; and (b) the shape of the drop size distribution must be assumed a priori. This article discusses new theory to interpret results from PGSE experiments and a novel procedure that couples diffusion measurements (PGSE) with transverse relaxation rate experiments (the so-called CPMG sequence) to overcome the above limitations. Results from experiments on emulsions of water dispersed in several crude oils are reported to demonstrate that the combined CPMG-PGSE method renders drop size distributions with arbitrary shape, the wateryoil ratio of the emulsion and the rate of decay of magnetization at the interfaces, i.e. the surface relaxivity. It is also shown that the procedure allows screening if the dispersion is oil-inwater (oyw) or water-in-oil (wyo) in a straightforward manner and that it is suitable to evaluate stability of emulsions. ᮊ
Selected cationic and amphoteric surfactants were effective in separating oil-in-water emulsions ... more Selected cationic and amphoteric surfactants were effective in separating oil-in-water emulsions representative of produced emulsions expected during a surfactant/polymer (SP) process for enhanced oil recovery. The aqueous phase of the emulsion contained an anionic surfactant blend, alcohol, and partially hydrolyzed polyacrylamide. Brine composition was a suitable mixture of formation brine with brines from the surfactant slug and polymer drive. The crude oil had an American Petroleum Institute (API) gravity of 31°. Bottle tests were conducted at ambient temperature, which is near the reservoir temperature. Conventional non-ionic demulsifier resins and polymeric cationic flocculants were not effective in removing oil from the aqueous phase. The water content of the oil phase was still well above specification upon heating the emulsions to 50-60°C. However, both oil and water phases of acceptable quality were obtained after 6 h of settling upon the addition of 200 ppm of octyltrimethylammonium bromide (C 8 TAB) at ambient temperature. Additionally, a commercial cationic surfactant at the same concentration yielded acceptable results for both phases in 2 h. Optical microscopy showed significant coalescence after only 1 min in the C 8 TAB system as the cationic surfactant reduced electrostatic repulsion among drops and shifted system phase behavior toward the balanced state between hydrophilic and lipophilic effects, actions well-known to reduce emulsion stability. Some amphoteric surfactants, such as cocobetaine, were also effective in separating these emulsions. The amount of cationic surfactant required could be reduced by adding it simultaneously with a non-ionic demulsifier resin. A commercial cationic surfactant was also found to significantly improve separation of emulsions produced during an alkaline/surfactant/polymer (ASP) process.
The procedure proposed by Packer and Rees (J. Colloid Interface Sci. 40 (1972) 206) to interpret ... more The procedure proposed by Packer and Rees (J. Colloid Interface Sci. 40 (1972) 206) to interpret pulsed field gradient spin-echo (PGSE) experiments on emulsions is commonly used to resolve for the distribution of droplet sizes via nuclear magnetic resonance (NMR). Nevertheless, such procedure is based on several assumptions that may restrict its applicability in many practical cases. Among such constrains, (a) the amplitude of the spin-echo (signal) must be influenced solely by the drop phase, and not by the continuous phase; and (b) the shape of the drop size distribution must be assumed a priori. This article discusses new theory to interpret results from PGSE experiments and a novel procedure that couples diffusion measurements (PGSE) with transverse relaxation rate experiments (the so-called CPMG sequence) to overcome the above limitations. Results from experiments on emulsions of water dispersed in several crude oils are reported to demonstrate that the combined CPMG-PGSE method renders drop size distributions with arbitrary shape, the wateryoil ratio of the emulsion and the rate of decay of magnetization at the interfaces, i.e. the surface relaxivity. It is also shown that the procedure allows screening if the dispersion is oil-inwater (oyw) or water-in-oil (wyo) in a straightforward manner and that it is suitable to evaluate stability of emulsions. ᮊ
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