(677e) CO2-in-Mineral Oil Emulsions, CH4-in-Mineral Oil Foams and N2-in-Mineral Oil Foams Stabilized By Novel Oil-Soluble Surfactants As Waterless Hydraulic Fracturing Fluids

Authors: 
Enick, R., University of Pittsburgh
Alzobaidi, S., University of Texas at Austin
Rodriguez, G., University of Pittsburgh
Lee, J. J., University of Pittsburgh
Lu, C., UT Austin
Da, C., Rice University
Harris, J., The University of Texas at Austin
Perry, R. J., Global Research, General Electric
Johnston, K., The University of Texas at Austin
Objectives/ Scope: Viscous, completely water-free, high pressure liquid CO2-in-oil (C/O) emulsions, methane-in-oil (M/O) foams and N2-in-oil (N/O) foams have been stabilized by novel, interfacially active, oil-soluble, polymeric surfactants. For example, for (C/O) emulsions, the surfactant is composed of an oleophilic long-chain alkyl pendant groups on a CO2-philic, oil-phobic, polydimethylsiloxane (PDMS) backbone. For (N/O) and (M/O) foams, neither N2 nor CH4 has appreciable solvent strength therefore the surfactant design is based upon oilphilic/oilphobic considerations. These emulsions and foams can serve as hydraulic fracturing fluids to eliminate the need for water and reduce formation damage caused by water.

Methods, Procedures: We designed and synthesized series of polymeric CO2-philic PDMS- oil-phobic alkyl surfactants for (C/O) emulsions; polymeric oil-philic/oil-phobic surfactants were designed for the N/O and M/O foams. 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 packed bed of 22 Darcy unconsolidated sand (quality up to 90 vol%).

Results, Observations, Conclusions: The novel, completely hydrophobic surfactants adsorb at the (C/O), (N/O) or (M/O) interface despite the very low interfacial tension (driving force) without surfactant present. For C/O emulsions, 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 oilphilic/oil-phobic balance, based on the decrease in the interfacial tension, were the only surfactants that stabilized the N/O and M/O foams.

Novelty/Additive Information: 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 general criteria for surfactant design. The surfactant design criteria are based on a fundamental understanding of the relationship between foam apparent viscosity in terms of interfacial properties and phase behavior, as well as foam texture. We also compare C/O emulsions and N/O and M/O foams to understand the role of gas solubility in oil on apparent viscosity. 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.