In this work, we show that single viscoelastic surfactants with or without switchable aqueous viscoelastic behavior can generate ultra-dry N2 or CO2 in water foam that can carry and transport proppants. We first show that viscoelastic solutions can be formed with nonionic, cationic, and zwitterionic surfactants given that the packing parameter of the surfactant head group area and tail group area are within the packing range of wormlike micelles. We then study the effect of concentration, and shear rate on the viscosity of the surfactant solution. The presence of wormlike micelles and the degree of entanglement for the surfactants were characterized and verified using complex rheology. The surfactants were tested for smart (switchable) viscoelastic behavior against external triggers, and the viscoelastic response of the surfactant solution is presented. The surfactants were then tested in a continuous flow apparatus for foam generation where the effects of gas type, temperature, tail length, beadpack permeability, smart aqueous behavior, and surfactant type were contrasted against the foam apparent viscosity, foam long term stability and foam bubble size. The ultra-dry foam apparent viscosity for the surfactants was as high as 300 cP with stability for over one day and bubble size as low as ~ 5 μm. These ultra-dry foams (with 96﹪ gas fraction) were able to carry and transport proppants in a model fracture (Hele-Shaw cell), which make them a promising fracturing fluid candidate.
The pressure gradient required to initiate and propagate a hydraulic fracture motivates the use of slickwater (water mixed with a small amount of friction reducer to increase the fluid flow) as fracturing fluid. For most proppants (made of silica or ceramics), suspension capacity in slickwater is quite low.1–3 Therefore, the injected proppants settle down quickly and leave a large portion of fracture unpropped, which reduces the fracturing process performance significantly. However, the use of polymer to increase the viscosity of water, to help suspending the proppants, increases the cost of hydraulic fracturing. Furthermore, the added polymers have drawn intense public scrutiny over the potential environmental impact of hydraulic fracturing operations. Moreover, polymer molecules can plug the small pores in fracture walls and damage the productivity of the fracture.4–6 In another solution, advanced proppant like ultra-lightweight proppant (ULWP)7 has been proposed as an alternative to conventional proppants since these proppants have lower settling velocity and require low viscosity fluids to transport. Even though ULWP penetrates to deeper into the matrix, their low structural strength limits their applicability to formation with low closure pressure.8 Moreover, small proppant fragments resulting from crushing of these materials offers lower fracture conductivity compared to conventional proppant.9, 10
