A novel foam system stabilized by hydroxylated multiwalled carbon nanotubes for enhanced oil recovery: Preparation, characterization and evaluation

Carbon nanotube (CNT) is one of promising materials for stabilizing foam. However, the aggregation of CNT seriously affects its foam-stabilizing performance. Herein, this study employed the ultrasonic waves to improve the dispersity of hydroxylated multiwalled carbon nanotube (HMCNT) in SDBS solution. The ultrasonic treatment can disentangle the HMCNT through cavitation and chip effects and the SDBS molecules adsorbed on the HMCNT may increase the electrostatic repulsion between nanotubes , leading to a good dispersion of HMCNT. Besides the conventional evaluations in bulk phase, this study developed a visualized cylinder filled with quartz glass beads to estimate the foam properties in porous media . Experimental results indicate that the novel SDBS/HMCNT foam has a good foaming and foam-stabilizing performance both in bulk solution and porous media. A series of analysis experiments have been conducted to reveal the foam-stabilizing mechnism of HMCNT, including the surface tension and dilational viscoelastic modulus measurements, and the optical microscope and fluorescence microscope observations. This study found that the SDBS-modified HMCNT can adsorb on the gas-liquid interface and gather around the bubbles. As a result, the dilational viscoelasticity and thickness of foam films increase, which help to slow down the gas diffusion rate and restrain the film drainage. Finally, the fractured-core flooding tests showed that the SDBS/HMCNT foam system can effectively plug the millimeter-sized cracks in low-permeability cores and have a good potential in enhanced oil recovery.