Highly Stable Polymer-Enhanced Pickering Foams for Hydraulic Fracturing Applications

Foamshave been used as fracking fluids for decades, but theirthermodynamic instability has always restricted subsurface applications,particularly in harsh reservoir conditions. Therefore, this studycomprehensively investigated the role of commonly used stabilizersin foaming behaviors, including the surfactant (APG), nanoparticle(CNCs), and polymer (XG), and their stabilizing behavior at the interfacewas also explored using molecular dynamics (MD) simulations. Our findingsindicated that the 0.5% XG-enhanced Pickering foam (0.5% APG + 1.0%CNCs) would be an exceptional fluid for fracking applications. Theformation of APG-CNC-XG gel-like networks among bubblessignificantly improved the stability of this liquid foam, and theliquid half-life could be extended by nearly 24 h, while the foamcan last for several days at 80 degrees C. Using MD simulations, weshowed that the coexistence and intramolecular interactions amongAPG, CNCs, and XG molecules generate a stronger hydrogen bonding networkin the thin film, significantly reducing water mobility, correspondingto the experimental observations. To explore the potential of foamsas fracking fluids, the sand-carrying capacity of two types of foamswas also evaluated; the polymer-enhanced Pickering foam was able tosuspend the sands for more than a day without participation. In thelab fracturing test, despite requiring a higher breakdown pressure,the polymer-enhanced Pickering foam reduces water consumption by almost20%. Moreover, the highly viscous foam also induced the wing-shapedfracture with a wider width along the hole. The deep insights gainedfrom this study will advance the application of foams as the frackingfluid in unconventional oil/gas reservoirs.