Influence of Thermal Treating Temperature on the Performance of EVA Wax Inhibitor for Changqing Shale Oil

Ethylene–vinyl acetate copolymer (EVA) is a kind of efficient wax inhibitor for waxy crude oil. To ensure good performance of EVA, thermal treating at temperatures ≥60 °C is needed for the doped waxy crude oil. Shale oil, which often contains a substantial amount of wax, is an important unconventional petroleum resource and has been exploited all over the world. To better guide the pipeline transportation of shale oil, in this paper, the effect of thermal treating temperature (40–60 °C) on the performance of EVA (with the fixed dosage of 50 ppm) wax inhibitor for specific Changqing shale oil was investigated through the rheological measurement, wax depositing test, microscopic observation of wax crystals, and particle size test of asphaltenes. The results showed that the performance of EVA is poor at thermal treating temperatures <50 °C. At the thermal treating temperatures ≥50 °C, adding 50 ppm EVA could outstandingly improve the flowability and inhibit the wax deposition of the shale oil. Increasing the thermal treating temperature to 50–60 °C greatly facilitates the adsorption of EVA molecules on the asphaltenes and then outstandingly reduces the particle size of asphaltenes (form the average size of 399.75 nm without EVA to 78.54 nm with EVA at a thermal treating temperature of 50 °C). Therefore, the thermal treatment at 50–60 °C favors the formation of more EVA/asphaltene composite particles. The formed EVA/asphaltene composite particles trigger the formation of larger and spherical-like wax crystals, thus further enhancing the performance of the EVA inhibitor.