Emulsion phase inversion from oil-in-water (1) to water-in-oil to oil-in-water (2) induced by in situ surface activation of CaCO3 nanoparticles via adsorption of sodium stearate

In the oil exploitation process, the conversion from water-in-oil emulsion to oil-in-water emulsion is usually needed for a better cementing quality after using the water-in-oil emulsion drilling fluid. Due to the advantages of both oil-external properties for drilling and water-external characteristics for completion, the reversible emulsion drilling fluids are being used in drilling industry. The researches about phase inversion of emulsion induced by nanoparticles and amphiphilic compounds are also being conducted. Using white oil-water system, emulsion stabilized by CaCO3 nanoparticles and sodium stearate was investigated. The raw CaCO3 nanoparticles were activated in situ by interaction with sodium stearate in aqueous solution. The mechanism of the in situ surface activation was accessed by means of emulsion characterization, adsorption measurement and contact angle. The results show that raw CaCO3 nanopartides can be activated in situ as emulsifiers by interaction with sodium stearate. With the monolayer and bilayer formed at the CaCO3 nanoparticles-water surface by absorption of different concentrations of sodium stearate, the wettability of the particles will transform from hydrophilicity to hydrophobicity and then back to hydrophilicity. The change of wettability may induce a phase inversion of emulsions from oil-in-water O/W (1) to water-in-oil W/O and re-invert to oil-in-water O/W (2). CaCO3 nanoparticles can thus be used as good stabilizers of both O/W and W/O emulsions once activated in situ by mixing with suitable amounts of sodium stearate. (C) 2015 Published by Elsevier B.V.