Pre-heating temperature induced flowability and wax deposition characteristics of crude oil adding wax inhibitors

Abstract

This paper investigated the effects of pre-heating treatment temperatures (Tpre) on the flowability and wax deposition characteristics of a typical waxy crude oil after adding wax inhibitors. It is found that there is little difference in wax precipitation exothermic characteristics of crude oils at different Tpre, as well as the wax crystal solubility coefficient in the temperature range of 25–30 °C. For the undoped crude oil, the flowability after wax precipitation gets much improved and the wax deposition is alleviated as Tpre increasing. At Tpre = 50 °C, the viscosity and wax deposition rate of crude oil adding wax inhibitors are higher than those of the undoped crude oil. When the Tpre increases to 60, 70, and 80 °C, the flowability of the doped crude oil are largely improved and the wax deposition is suppressed with the Tpre increase, but the wax content of wax deposit increases gradually. It is speculated that, on the one hand, the Tpre increase helps the dispersion of asphaltenes into smaller sizes, which facilitates the co-crystallization with paraffin waxes and generates more aggregated wax crystal flocs. This weakens the low-temperature gel structure and increases the solid concentration required for the crosslink to form the wax deposit. On the other hand, the decrease in viscosity increases the diffusion rate of wax molecules and accelerates the aging of wax deposits. The experimental results have important guiding significance for the pipeline transportation of doped crude oils.