Effect of Thermal Treatment Temperature on the Flowability and Wax Deposition Characteristics of Changqing Waxy Crude Oil

摘要

The influence of thermal treatment temperature on the flowability and wax deposition characteristics of Changqing waxy crude oil was researched in detail through pour point/rheological tests, a cylindrical Couette wax deposition experimental device, DSC analyses, asphaltenes stability tests, and microscopic observations. It is found that the flowability of the crude oil can be greatly improved through increasing the thermal treatment temperature. Meanwhile, the wax deposition rate of the crude oil can be outstandingly inhibited with the increase of thermal treatment temperature from 50 to 70 degrees C. Moreover, the flow regime can also influence the wax deposition characteristics. Under cold flow regime (22 degrees C/12 degrees C), the structure of formed wax deposits is homogeneous while the aging of the wax deposits is not obvious. Under hot flow regime (30 degrees C/20 degrees C), the aging of the wax deposits is obvious, but a heterogeneous two-layer structure exists in the formed wax deposits at the thermal treatment temperatures 50 and 60 degrees C, with a hard/thin bottom layer and a relatively soft/thick surface layer. With the increase of thermal treatment temperature to 70 degrees C, the two-layer wax deposit structure cannot be identified due to the extremely thin wax deposit thickness. Increasing the thermal treatment temperature can disperse and activate the asphaltenes in the crude oil; the activated asphaltenes have stronger interactions with waxes and then decrease the WAT of the oil and change the precipitated wax crystals' morphology further, hence dramatically improving the crude oil flowability and inhibiting wax deposition. Under hot flow regime, the two-layer wax deposit structure is mainly triggered through the diffusion of wax molecules and asphaltenes from the bulk oil into the wax deposits. Under cold flow regime, the asphaltenes have already coprecipitated with wax molecules into big wax flocs, which is difficult to diffuse from the bulk oil into the already existed wax deposits. Meanwhile, the aggravated flowability of bulk oil under cold flow regime further hinders the diffusion of wax molecules into the interior of the wax deposit. Therefore, the two-layer wax deposit structure cannot be found under cold flow regime.