(159f) Coalescence and Destruction of Nanoparticle Stabilized Foams after Hydraulic Fracturing Via Pressure Reduction

Foams, dispersions of gases in liquids, are great substitutes for conventional hydraulic fracturing fluids. Conventional methods use water, chemical additives and thickeners such as guar gum to increase viscosity of the fluids. This enables the pad to carry proppants into the fractures. The problem with hydraulic fracking processes appears during flowback of the fracking fluid. Although during injection step having high viscosity is essential to carry sand into the fracking zone, during flowback high viscosity of the pad can displace sand away from the fracture and clog the passages designed for the flow of shale gas and oil. Foams are considered as alternative smart pads. They significantly reduce water consumption during fracking jobs; exhibit high viscosity to move proppants into the fracking zone; and their physical properties are tunable either by changing macroscopic variables such as pressure or tuning microscopic chemistry at gas-liquid interface. Nanoparticle stabilized foams are generated at high pressures while their texture and stability appears to be a strong function of pressure. Moreover, addition of polymers and surfactants synergistically boosts foam generation. Gas bubbles are separated by liquid lamellas while disjoining pressure at liquid lamella is a function of interactions such as attractive van der Waals forces and repulsive electrostatic and oscillatory forces. The nanoparticles with diameters between 5-28 nm are adsorbed at gas-liquid interface to protect gas bubbles from coalescence while adsorption of the nanoparticles is essentially irreversible. During gas expansion the surface density of nanoparticles is reduced until they meet a threshold density at which the neighboring bubbles will coalesce into one and foam catastrophically collapse. Here we have developed a model to determine optimum pressure profiles to keep foams stable during fracture growth and break them during flowback.