Highly Stable Polymer-Enhanced Pickering Foams for Hydraulic Fracturing Applications

Foams have been used as fracking fluids for decades, but their thermodynamic instability has always restricted subsurface applications, particularly in harsh reservoir conditions. Therefore, this study comprehensively investigated the role of commonly used stabilizers in foaming behaviors, including the surfactant (APG), nanoparticle (CNCs), and polymer (XG), and their stabilizing behavior at the interface was also explored using molecular dynamics (MD) simulations. Our findings indicated that the 0.5% XG-enhanced Pickering foam (0.5% APG + 1.0% CNCs) would be an exceptional fluid for fracking applications. The formation of APG–CNC–XG gel-like networks among bubbles significantly improved the stability of this liquid foam, and the liquid half-life could be extended by nearly 24 h, while the foam can last for several days at 80 °C. Using MD simulations, we showed that the coexistence and intramolecular interactions among APG, CNCs, and XG molecules generate a stronger hydrogen bonding network in the thin film, significantly reducing water mobility, corresponding to the experimental observations. To explore the potential of foams as fracking fluids, the sand-carrying capacity of two types of foams was also evaluated; the polymer-enhanced Pickering foam was able to suspend the sands for more than a day without participation. In the lab fracturing test, despite requiring a higher breakdown pressure, the polymer-enhanced Pickering foam reduces water consumption by almost 20%. Moreover, the highly viscous foam also induced the wing-shaped fracture with a wider width along the hole. The deep insights gained from this study will advance the application of foams as the fracking fluid in unconventional oil/gas reservoirs.