Asphaltene dispersants weaken the synergistic modification effect of ethylene-vinyl acetate and asphaltene for model waxy oil

Abstract

It has been proved that colloidal asphaltene and polymer pour point depressants (PPD) synergistically and dramatically modify the rheology of model waxy oil. In the crude oil recovery process, amphiphilic asphaltene dispersant (AD) is often added to inhibit asphaltene deposition, the added AD should affect the synergistic effect of asphaltene and PPD and need to be further investigated. In this work, several asphaltene dispersants were added to the model waxy oil and their influence law on the modification effect of ethylene–vinyl acetate (EVA) was systematically evaluated. The results indicated that AD does not affect the modification effect of EVA alone, but significantly deteriorates the synergistic modification function between EVA and asphaltene. Further, the electron cloud density of AD molecules was calculated using molecular dynamics, revealing the mechanism by which AD influences the modification effect of polymer PPD: the effect of EVA in improving the low-temperature rheology of model wax oil is primarily determined by the adsorption of EVA with asphaltene, while the existence of competitive adsorption between AD and EVA will inhibit the modification effect of EVA. The advantage of AD molecules in the competitive adsorption process increases with their electronegativity, making their dispersion effect on asphaltene and suppression of EVA modification ability more pronounced. The discovery of this phenomenon sheds light on the dispersion stability of asphaltene dramatically affects the performance of PPD, which helps develop new efficient crude oil modifiers.