Simultaneous Control of Formation and Growth of Asphaltene
Solids and Wax Crystals Using Single-Walled Carbon Nanotubes: an Experimental
Study under Real Oilfield Conditions
posted on 2021-08-26, 20:30authored bySaber Mohammadi, Fatemeh Mahmoudi Alemi
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.