Emulsion Breakage Mechanism Using Pressurized Carbon Dioxide

The production of water during crude oil extraction may result in the formation of stable water-in-oil emulsions. Such emulsions are problematic for a variety of reasons; for example, they increase the fluid viscosity and hence the pumping costs. Previously, Ling; [NMR Studies of the Effect of CO2on Oilfield Emulsion Stability. Energy Fuels2016, 307, 5555–5562] have shown that treating these water-in-crude oil emulsions with subcritical CO2at 50 bar can lead to their breakage. These measurements utilized benchtop NMR pulsed field gradient (PFG) techniques to monitor the evolution in the emulsion droplet size distribution, which is a precursor to emulsion breakage. Experimental limitations meant, however, that the measurements were performed only following depressurization of the applied CO2and as such were unable to directly distinguish between two potential mechanisms for emulsion breakage as proposed in the literature: (i) CO2bubble formation within the water droplets upon depressurization or (ii) the removal of surface-adsorbed asphaltenes. Here, we develop a new apparatus and perform the required emulsion droplet sizing measurements using NMR PFG techniques with the sample under pressure during CO2treatment. A distinct growth in the droplet size was observed during the treatment, which is consistent with mechanism (ii); however, further growth was observed following depressurization and shown to be consistent with mechanism (i); thus, both are relevant. The efficacy of the treatment was then further assessed for the case of NaCl addition to the aqueous phase.