Wax deposition in crude oil pipelines is a challenging issue for the oil industry. Several factors may affect wax deposition, such as wax concentration, cooling rate, pressure, and flow. How shear rate may alter wax appearance temperature (WAT) and gel strength has not been widely studied. We investigated six samples of light mineral oil and paraffin wax at different wax concentrations. Temperature ramp experiments identified a jump in viscosity related to wax appearance under steady shear. Yield stress, on the other hand, was measured using oscillatory sweep experiments. WAT increased significantly by increasing wax concentration. Changing concentration from 5 to 50 wt% resulted in a~ 20 oC increase in WAT at shear rate 1000 s-1 and also at static conditions. Viscosity after wax formation increased with concentration to the power of 1.5 at shear 10 s-1. Lowering cooling rate from 10 to 0.2 oC/min under shear rate of 100 s-1 increased WAT up to 4 oC. Shear rate had a more modest effect on WAT of a ~ 2 oC decrease when shear rate increased from 1 to 1000 s-1. However, shear rate has a more significant effect on the yield stress of formed gels. An increase in shear rate from 0 to 1000 s-1 caused the yield stress to decrease from 415 to 8 Pa. Wax structure breaks adhesively when cooling rate increases from 0.2 to 5 oC/min. Wax phase changes were also studied using DSC and static phase behavior to quantify the wax appearance. Overall, adding shear rate to phase behavior studies could help the oil industry better understand wax flow assurance issues.

Shear alters wax appearance in mineral oil + paraffin wax mixtures

ACS Spring Meeting 2021

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