Surfactant-Only Stabilized Dispersions of Multiwalled Carbon Nanotubes in High-Electrolyte-Concentration Brines

Abstract

Multiwalled carbon nanotubes (MWNTs) exhibit promising properties for potential applications in oil production. Because of their substantial surface area, they could be used as carriers for catalysts or chemicals into subsurface oil and gas zones to change the properties of reservoir fluids or rock. A prerequisite for utilizing the MWNT in reservoir applications is to generate stable aqueous-phase dispersions that are well-dispersed and able to propagate successfully through the reservoir medium. In this study, different types of surfactants were investigated for their ability to disperse MWNTs in high-ionic-strength solutions typical of oil reservoirs up to 10% American Petroleum Institute (API) brine (8 wt % NaCl and 2 wt % CaCl 2 ). Stable nanotube dispersions in deionized water were achieved with the anionic surfactants evaluated. Compression of the electrical double layer, however, at high ionic strength, e.g., >3 wt % electrolytes, led to rapid aggregation of the anionic surfactant-aided nanotube dispersion. This study showed that by dispersing nanotubes in nonionic surfactant such as alkylphenol polyethoxylates with a large number of ethylene oxide (EO) groups, stable MWNT dispersions were obtained in 10 wt % brine. In the sandpack column test, a binary surfactant formulation, which consisted of a nonionic surfactant and an anionic surfactant in the proper ratios, exhibited an excellent capability to propagate MWNT, with 96% of the injected nanotubes recovered in the effluent. The adsorption density of surfactants onto MWNT was determined to be 9 molecules/nm 2 from the shift of the CMC value in the surface tension measurement. This study reveals that steric repulsion between the nanotubes could eliminate the aggregation of dispersed MWNT under the high-electrolyte-concentration condition, whereas nanotube−nanotube and nanotube−sand surface electrical repulsion could assist in the transport of the MWNT dispersion through porous media.

Dispersion of Multi-Walled Carbon Nanotubes by Polymers with Carbazole Pendants

“…To widely exploit the CNTs, individualizing CNTs is required to obtain a homogeneous and stable dispersion. , Compared with covalent functionalization of nanotube surfaces, dispersant-assisted dispersion via noncovalent interaction with nanotubes is more appealing. Dispersant-assisted dispersion not only improves the dispersibility and stabilization of CNTs but also preserves the intrinsic properties of CNTs. , For this strategy, the small molecule-based surfactants, − polymers, − and biomacromolecules are frequently chosen as dispersants to debundle or disperse CNTs. Generally, the dispersants stabilize the CNT dispersions mainly through electrostatic repulsion, steric repulsion, or depletion forces. , …”

Propagation of Surfactant‐Dispersed Multiwalled Carbon Nanotubes in Porous Media

“…In our previous studies, it was seen that nonionic surfactants NP40EO and LA40EO exhibited excellent suspendability for MWNT in aqueous solution at high salinity conditions (Chen et al, ). The bulky hydrophilic head groups, i.e., ethylene oxides, present a strong steric repulsion, thus effectively stopping the flocculation of dispersed nanotubes in the solution.…”

“…An ultraviolet–visible (UV–Vis) spectrophotometer (Thermoscientific, Genesys10s, Waltham, MA, USA) was used to measure the concentration of MWNT in stable dispersion at a wavelength of 800 nm. The details can be found elsewhere (Chen et al, ). The MWNT concentration was 80 ± 2 mg L −1 in all prepared dispersion samples.…”

“…In most cases, CNT attachment to the porous media was irreversible (Lu et al, ), and therefore, excessive CNT deposition should be avoided/minimized in the formation; otherwise, accumulation of CNT may result in severe permeability (formation) damage. Our previous study demonstrated the superiority of some nonionic surfactants with very long ethylene oxide groups, such as linear alcohol ethoxylates and alkylphenol ethoxylates, in the dispersion of MWNT under elevated temperature and salinity conditions (Chen et al, ; Chen et al, ). In this work, laboratory experiments were performed to investigate the transport of surfactant‐aided MWNT dispersions in different porous media by varying in situ conditions.…”

Polymer-Stabilized Multi-Walled Carbon Nanotube Dispersions in High-Salinity Brines

“…Nanoparticles have fascinating properties as a result of their interfacial activity at the water/oil interface and, therefore, have received significant attention as a result of potential applications in reservoir development. − Nanoparticles can be modified to adsorb selectively, resulting in changes of rock wettability, which can impact relative permeability of the reservoir. − Carbon nanotubes (CNTs) have the ability to stabilize water/oil Pickering emulsions and change oil-phase properties by performing selective catalysis. ,, Earlier work investigated the use of nanoparticles as tracers or reporters for reservoir heterogeneity. , Rheological studies of different nanoparticles have demonstrated potential uses in hydraulic fracturing technology. − Earlier work also demonstrated the ability to stabilize single-walled CNT dispersion using gum arabic (GA) alone in deionized water, where electrostatic repulsion dominates between the dispersed CNT strands . A wide range of surfactants are also capable of dispersing CNTs in deionized aqueous solutions. − Numerous papers have investigated the dispersion chrcteristics of CNTs in terms of CNT concentration, solution pH, and surface modification of CNTs . Although it is well-understood that inorganic salts cause flocculation of dispersed CNTs, the effect of high ionic strength [high salinity or high total dissolved solids (TDS)] has not been covered extensively.…”