Viscosifying modified proppant system for carbon dioxide based fracturing fluids

A method of preparing a viscous hydraulic fracturing fluid, the method comprising:

• combining a CO2-based fluid consisting of at least 30 weight percent carbon dioxide as either supercritical carbon dioxide or subcritical carbon dioxide and optionally at least one of nitrogen, dimethyl ether, or hydrocarbons with a viscosifying proppant to form the viscous hydraulic fluid, in which:
• the viscosifying proppant comprises proppant particles coated with a CO2-philic coating;
• the CO2-based fluid has a first viscosity at a pressure of less than or equal to 1000 pounds per square inch (psi) and a temperature of less than or equal to 32° C.;
• the CO2-philic coating comprises a CO2-philic material chosen from polysaccharide acetates, partially fluorinated oxygen-containing polymers, oxygenated polymers, crosslinked oxygen-containing polystyrenes, or combinations of any of these, where the partially fluorinated oxygen-containing polymers are selected from the group consisting of polymers of 2-(N-ethylperfluorooctane-sulfonamido) ethyl acrylate, polymers of 2-(N-ethylperfluorooctane-sulfonamido) ethyl methacrylate, polymers of 2-(N-methylperfluorooctane-sulfonamido) ethyl acrylate, polymers of 2-(N-methylperfluorooctane-sulfonamido) ethyl methacrylate, polymers of 1,1′-dihydroperfluorooctyl acrylate, polymers of 1,1′-dihydroperfluorooctyl methacrylate, polymers of 1,1′,2,2′-tetrahydroperfluoroalkylacrylates, polymers of 1,1′,2,2′-tetrahydroperfluoroalkyl-methacrylates, polymers of hexafluoropropylene oxide, polymers of perfluorocyclohexane oxide, polymers of perfluoro(propyl vinyl ether), and polymers of perfluoro(methyl vinyl ether),
• by which:
• a solvable portion of the CO2-philic coating dissociates from the proppant particles, associates with the carbon dioxide in the CO2-based fluid, and viscosifies the CO2-based fluid;
• the viscous hydraulic fluid has a second viscosity as measured at least 30 minutes after the combining with the viscosifying proppant and at a pressure of less than or equal to 1000 psi and a temperature of less than or equal to 32° C.;
• and
• the second viscosity is at least 25% greater than the first viscosity and is sufficient to suspend the particles within the CO2-based fluid;
• the CO2-philic coating does not dissociate from the proppant particles when the viscosifying proppant is added to a water-based fluid comprising at least 30% water.