Modified graft copolymers based on ethylene vinyl acetate as depressants for waxy crude oil and their effect on the rheological properties of oil

Abstract

In this work, modified ethylene-vinyl acetate (EVA)-based copolymers were synthesized by graft copolymerization of hydrophobic monomers onto commercial EVA using a low energy electron beam (EB). The mechanism of graft copolymerization was studied by the spin trap method using a model reaction of the interaction of a tert-butoxy radical with an EVA copolymer. The results show that the main contribution to the initiation of graft copolymerization is made by the reactions of hydrogen abstraction from the methine CH groups of the vinyl acetate units. Oil from the Kumkol region treated with PPD showed better rheological properties, lower pour point temperatures, as well as lower wax content when tested on a cold finger, and better performance on the transportation route of the Kumkol - Karakoin - Shymkent. Moreover, EVA-based graft copolymers (gEVAp) performed better PPD than those obtained for commercial pour-point depressant (PPD). The rheological parameters of oil have been dramatically improved, which can be characterized as better oil pumpability in the cold season, which reduces the load on mainline pumps and saves energy for the transporting company. The pour point of the tested oil dropped from 12 to −3 °C, which led to the formation of wax crystals of the regular, compact platelet shape. Field tests using pigs showed significantly less wax deposited along the pipeline.