Liquid Foam Stabilized by a CO₂-Responsive Surfactant and Similarly Charged Cellulose Nanofibers for Reversibly Plugging in Porous Media

Abstract

CO2 foams are of great importance in oil recovery but challenging in some aspects like long-term stabilization and time-separated conflict. In this work, a stability-enhanced switchable foam was fabricated using bis-(2-hydroxyethoxy) olefine amine (BOA) and trace amounts (0.05 wt %) of cationic-modified cellulose nanofibers (CCNFs). The CCNF was developed using sequentially functionalized CNF with diamine groups, which were essential to promote the aqueous dispersibility and a key for strengthening the stabilization of foam. The combination of similarly charged CCNFs and BOA in the presence of CO2 contributed to both surface activity and viscoelasticity. It was demonstrated that CCNFs were entangled and stacked to form the compact films and possessed the ability to costabilize the lamellae, as observed by microscopic studies. In addition, the intermolecular H-bonds were promoted in the binary system after being protonated by CO2 and thus balancing the electrostatic forces, as explored by spectroscopy characterizations. The soft fibrous structure of the CCNF was also capable of wrapping gas bubbles in the form of a functional membrane with both low gas permeability and high surface potential, which slowed down the coarsening and coalescence. Of particular interest is that the reversible protonation state of CCNF-BOA complexes upon the alternate treatment with CO2/N2 led to reversible fast foaming/defoaming, which would be beneficial to construct the steerable plugging in the sand pack. This work is expected to provide a new direction and application of the CO2 responsive foam stabilized by similarly charged nanocellulose fibers in oilfield development.

Water-Induced Cellulose Nanofibers/Poly(vinyl alcohol) Hydrogels Regulated by Hydrogen Bonding for In Situ Water Shutoff

“…As expressed in the section of the mechanical strength of PVA−CNF hydrogel in acid−base and salt-involved conditions in the Supporting Information (Figure S10), it can be acquired that PVA−CNF hydrogel can maintain its network structure without serious damage in the range of pH = 2−13 and the saline environments, which indicated that PVA−CNF hydrogel has the excellent stability and adaptability to the harsh water environment of the reservoir. It is well known that the application of hydrogel for water shutoff in oilfields is as follows: the polymer-based sol of relatively low viscosity (<10 mPa•s) was injected in the high-permeable zone of the reservoir and it in situ polymerizes to form hydrogel with time or temperature in the micro-channels, 32 thus acting as a physical barrier to hinder water production or to reduce the permeability of high-permeable zone.…”