(644f) Liquid CO2-in-Mineral Oil Emulsions Stabilized By Siloxane-Long Chain Alkyl Surfactants and Application As a Waterless Hydraulic Fracturing Fluid

Authors: 
Alzobaidi, S., University of Texas at Austin
Lee, J. J., University of Pittsburgh
Jiries, S., University of Pittsburgh
Beckman, E. J., University of Pittsburgh
Rodriguez, G., University of Pittsburgh
Perry, R. J., Global Research, General Electric
Johnston, K. P., The University of Texas at Austin
Enick, R., University of Pittsburgh
CO2 has long been considered an attractive fracturing fluid for water-sensitive formations, but the very low viscosity of CO2 (e.g. 0.1 mPa s at 25oC and 2500 psig) inhibits the formation of large hydraulic fractures and makes it difficult to transport high concentrations of large proppant particles into fractures. The CO2-rich waterless emulsions described in this study may be a practical way of dramatically increasing the apparent viscosity of CO2 for fracturing applications while offering an easy way to add both the surfactant and the proppant to the mineral oil at ambient pressure (rather than blending surfactant and/or proppant with high pressure CO2 at the surface).

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 – 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.