Simultaneous Control of Formation and Growth of Asphaltene Solids and Wax Crystals Using Single-Walled Carbon Nanotubes: an Experimental Study under Real Oilfield Conditions

Asphaltene and wax depositions in oil production systems have been recognized as the most serious flow assurance concern of petroleum engineering. Despite the several chemicals offered for treatment of issues induced by these organic deposits, proposing a single efficient chemical to control simultaneously both asphaltene and wax precipitation has not been attended yet. Here, single-walled carbon nanotubes (SWCNTs) were synthesized to assess their effects on controlling the formation and size growth of asphaltene particles and wax crystals in live oil under realistic production conditions. SDS experiments showed that during depressurization at 125 °C, the asphaltene onset pressure decreased from 5946 psi in untreated live oil to 4375 in treated live oil with 100 ppm SWCNTs. High-pressure microscopy revealed that SWCNTs efficiently controlled the growth of asphaltene aggregates and reduced the size of asphaltenes in live oil during depressurization at 125 °C. This is ascribed to the strong π–π interactions between the aromatic rings of SWCNTs and electron clouds of asphaltenes. Results of cross-polarized microscopy showed that SWCNTs at an optimum concentration of 75 ppm postponed the wax formation temperature and gelation point from 32.6 and 21.5 °C to 23.2 and 14.7 °C, respectively. In addition, the morphology of the wax crystals with an average size of 756 nm in untreated oil changed from dense spherical-like into thin needle-like with an average size of 86 nm in treated oil with SWCNTs at 75 ppm. The changes in the wax crystal size and structure via X-ray powder diffraction analysis after crude oil treatment with SWCNTs confirm interactions between the carbon nanotubes and active sites of the wax crystals. The findings of this research prove that synthesized carbon nanotubes can be used as efficient inhibitor and dispersant agents for stabilizing the waxes and asphaltenes in live oil with controlling the rate of aggregation under high-pressure–high-temperature conditions.