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NMR Studies of the Effect of CO2 on Oilfield Emulsion Stability

Ling, Nicholas N. A., Haber, Agnes, Hughes, Thomas J., Graham, Brendan F., May, Eric F., Fridjonsson, Einar O., Johns, Michael L.
Energy & Fuels 2016 v.30 no.7 pp. 5555-5562
carbon dioxide, droplet size, emulsions, gases, methane, models, nitrogen, nitrous oxide, nuclear magnetic resonance spectroscopy, oil fields, oils, petroleum, solubility, surfactants, transportation
Formation of water-in-crude oil emulsions is a pervasive problem for crude oil production and transportation. Here we investigate the effectiveness of a comparatively low pressure CO₂ treatment in terms of breaking these water-in-crude oil emulsions. To this end, we used unique benchtop nuclear magnetic resonance (NMR) technology to measure the droplet size distribution (DSD) of the emulsions. Treatment with 50 bar CO₂ for 2 h resulted in significant emulsion destabilization; this was replicated when CO₂ was replaced by N₂O, which has a solubility in both the aqueous and oil phases similar to that of CO₂. Low solubility gases, N₂ and CH₄, by contrast had no effect on emulsion stability. Treatment with CO₂ was also found to have no effect on a model water-in-paraffin oil emulsion stabilized by a synthetic surfactant (Span 80). Collectively, this supported the hypothesis that emulsion destabilization results from CO₂ precipitation of asphaltenes as opposed to emulsion droplet film disruption during depressurization, which are the two competing theories reported in the literature to explain the observed supercritical CO₂ destabilization of emulsions. Treatment of a water-in-crude oil emulsion featuring partial removal of asphaltenes from the oil phase was consistent with this hypothesis, as the effect of the CO₂ treatment on emulsion destabilization was significantly more pronounced.