Viscous, water-free, high pressure liquid CO2-in-oil (C/O) emulsions and N2-in-oil (N/O) foams have been stabilized by interfacially active, oil-soluble, polymeric surfactants with oleophilic long-chain alkyl pendant groups on a CO2-philic polydimethylsiloxane (PDMS) backbone.These emulsions and foams can eliminate the need for water in hydraulic fracturing fluids and reduce formation damage. We designed and synthesized series of polymeric surfactants, which are comprised of a PDMS backbone with multiple pendent oleophilic alkyl segments. The emulsions/foams were formed by either mixing with an impeller (quality or volume fraction up to 60 vol%) or by simultaneously co-injecting the fluids through a beadpack of 22 Darcy unconsolidated sand (quality up to 90 vol%). The novel, completely hydrophobic surfactants adsorb at the (C/O) or (N/O) interface despite the very low interfacial tension (driving force) without surfactant present. At a concentration of 2 wt % in oil, the surfactant stabilizes the emulsions and no gelation of oil occurs. The 50-90% quality C/O emulsions, with CO2 droplet sizes in the 5 – 150 micron range, exhibited an apparent viscosity of about 3 - 18 cP at 25oC and 2500 psia as determined with falling ball and capillary viscometers. The emulsions were stable for over a day as indicated by photographs and determination of the bubble size with microscopy. In contrast, N/O foams had an apparent viscosity ranging from 15-65 cP. Oil-soluble surfactants with optimum CO2 or N2-philic and oil-phobic balance, based on the decrease in the interfacial tension, were the only surfactants that stabilized the oil emulsions. We have addressed a major limitation in the generation and stabilization non-aqueous CO2 and N2 energized emulsions and foams for water-sensitive formations, by providing criteria for surfactant design. The surfactant design criteria is based on a fundamental understanding of the relationship between foam apparent viscosity in terms of interfacial properties, phase behavior, as well as foam texture. We also compare C/O and N/O emulsions and foams apparent viscosity versus gas solubility in oil. The waterless, viscous emulsions and foams are hydraulic fracturing fluids that offer an efficient way to add both the novel surfactant and the proppant to the mineral oil at ambient pressure (rather than blending surfactant and/or proppant with high pressure CO2 or N2) for improved oil or gas recovery in water-sensitive formations.

High pressure CO2-in-mineral oil emulsions and N2-in-mineral oil foams stabilized by polydimethylsiloxane-based surfactants as a waterless hydraulic fracturing fluid

255th National Meeting (2018)

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