459877 Novel Surfactants for Stabilizing CO2-in-Oil Emulsions and Natural Gas-in-Oil Foams for Dry Hydraulic Fracturing

Tuesday, November 15, 2016: 4:30 PM
Union Square 25 (Hilton San Francisco Union Square)
Robert M. Enick1, Jason J. Lee1, Stephen Cummings1, Eric J. Beckman1, Robert J. Perry2, Shehab Alzobaidi3 and Keith P. Johnston3, (1)Chemical and Petroleum Engineering, University of Pittsburgh, Pittsburgh, PA, (2)Global Research, General Electric, Niskayuna, NY, (3)McKetta Department of Chemical Engineering, The University of Texas at Austin, Austin, TX

Liquid CO2 is an attractive fluid for many hydraulic fracturing applications because it contains no water (i.e., it is “dry” does not damage water-sensitive sandstone or shale formations) and it is easily removed from the wellbore after the fracturing process is complete. Despite these attributes, very few “dry” fracks with liquid CO2 are conducted. The foremost technical reason that pure CO2 remains an ineffective dry fracking fluid is its very low viscosity at typical fracturing pressures. Based on models of rock mechanics, a fracture formed with pure CO2 is significantly smaller than fractures formed with “slickwater”. Further, the low viscosity of CO2 hinders its ability to effectively transport high concentrations of large proppant particles into the fractures. There are several companies that combine liquid CO2 with an aqueous surfactant solution to generate CO2-in-water emulsions that have a high apparent viscosity. However, the presence of water in these CO2-in-water foams renders them “wet”. We propose a “dry foam” composed of bubbles of liquid CO2 within films of an oil phase. Several research teams have previously explored CO2-in-oil emulsions that were stabilized with conventional surfactants composed of hydrophilic and hydrophobic segments, often with the addition of water or ethylene glycol to the mixture. However the dissolution of these surfactants in the oil often results in gelation of the oil that makes it difficult to pump, and upon mixing of the oil + surfactant mixture with CO2 the resultant emulsions are often unstable. Therefore we have designed and synthesized novel non-fluorous surfactants for stabilizing CO2-in-oil emulsions. In accordance with Bancroft’s rule, these surfactants are more oil-soluble than CO2-soluble. Further, each surfactant has two hydrophobic segments; one that is CO2-philic and oil-phobic, while the other segment is oil-philic and CO2-phobic. Finally, the surfactants have also been designed to not gel the oil. High pressure CO2-in-mineral oil emulsion stability measurements and high pressure CO2-mineral oil IFT results will be presented that demonstrate the remarkable efficacy of these novel surfactants relative to conventional surfactants.

Preliminary results for novel surfactants designed to stabilize dry natural gas-in-oil foams will also be presented. Such foams may be attractive for dry fracturing because the foam would have a much higher apparent viscosity than pure methane, natural gas could be obtained from nearby producing wells, and the flowback hydrocarbons (natural gas and oil) would mix with the produced gas and oil.

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See more of this Session: Emulsions and Foams II
See more of this Group/Topical: Engineering Sciences and Fundamentals