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    Carbon dioxide-in-oil emulsions stabilized with silicone-alkyl surfactants for waterless hydraulic fracturing

    Year: 2018

    Journal: J. Colloid Interface Sci., Volume 526, SEP 15, page 253–267

    Authors: Alzobaidi, Shehab; Lee, Jason; Jiries, Summer; Da, Chang; Harris, Justin; Keene, Kaitlin; Rodriguez, Gianfranco; Beckman, Eric; Perry, Robert; Johnston, Keith P.; Enick, Robert

    Organizations: U.S. Department of Energy - Advanced Research Project Agency-Energy (ARPA-E) [DE-AR0000292]; National Science Foundation Graduate Research Fellowship Program [DGE-1610403]; Welch Foundation [F-1319]; Department of Energy Center for Subsurface Energy Security [DE-SC0001114]

    Keywords: Waterless emulsions; Carbon dioxide in oil emulsions; Carbon dioxide-oil interface; Emulsion stability; Silicone; PDMS; Non-fluorous; Comb polymers

    The design of surfactants for CO2/oil emulsions has been elusive given the low CO2-oil interfacial tension, and consequently, low driving force for surfactant adsorption. Our hypothesis is that waterless, high pressure CO2/oil emulsions can be stabilized by hydrophobic comb polymer surfactants that adsorb at the interface and sterically stabilize the CO2 droplets. The emulsions were formed by mixing with an impeller or by co-injecting CO2 and oil through a beadpack (CO2 volume fractions (phi) of 0.50-0.90). Emulsions were generated with comb polymer surfactants with a polydimethylsiloxane (PDMS) backbone and pendant linear alkyl chains. The C-30 alkyl chains are CO2-insoluble but oil soluble (oleophilic), whereas PDMS with more than 50 repeat units is CO2 -philic but only partially oleophilic. The adsorbed surfactants sterically stabilized CO2 droplets against Ostwald ripening and coalescence. The optimum surfactant adsorption was obtained with a PDMS degree of polymerization of similar to 88 and seven C-30 side chains. The emulsion apparent viscosity reached 18 cP at a phi of 0.70, several orders of magnitude higher than the viscosity of pure CO2, with CO2 droplets in the 10-150 mu m range. These environmentally benign waterless emulsions are of interest for hydraulic fracturing, especially in water-sensitive formations. (C) 2018 Elsevier Inc. All rights reserved.
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