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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.