(644f) Liquid CO2-in-Mineral Oil Emulsions Stabilized By Siloxane-Long Chain Alkyl Surfactants and Application As a Waterless Hydraulic Fracturing Fluid
A water-free, high pressure CO2-in-oil emulsion (sometimes referred to as foam) of liquid CO2 droplets within continuous films of mineral oil can be stabilized by a novel, completely hydrophobic, oil-soluble surfactant. The surfactant comprised of an oleophilic (CO2-phobic) alkyl segment and a CO2-philic oleophobic polydimethylsiloxane segment adsorbs at the CO2-oil interface despite the very low interfacial tension without surfactant present. The surfactant increases the oil viscosity by 40% at a concentration of 2 wt % aiding emulsion stabilization. The emulsions were formed by either mixing with an impeller (CO2 quality or volume fraction up to 60 vol%) or by simultaneously co-injecting the liquids through a packed bed of 22 Darcy unconsolidated sand (CO2 quality up to 90 vol% with CO2 droplet sizes in the 20 â 150 micron range). These 50-90% quality CO2-in-mineral oil emulsions exhibited an apparent viscosity of about 3 - 18 cP at 25oC and 2500 psia with a falling ball and capillary viscometer. Ultimately, these emulsions could be used to greatly reduce water requirements and minimize wastewater produced in hydraulic fracturing.