Visualization of thermal removal mechanism of paraffin deposits: Providing guidelines for minimum temperature requirements

Abstract

Active heating is increasingly explored as a cost-effective strategy for managing wax deposition in production flowlines. While active heating is widely used across the industry to maintain or raise the temperature of the production fluid above the wax appearance temperature (WAT), there exists no clear understanding of the mechanism and guidelines for wax removal using active heating technology. Currently, operators tend to aim for temperatures far above the WAT to ensure removal. There is an interest in the finding of the actual temperature targets. If these can be defined, lowering current operational targets, reducing energy requirements, and therefore reducing costs becomes possible. To this end, a novel dynamic microscopic visualization technique is employed to understand the removal mechanism as the deposit is exposed to varying removal temperatures. As the removal temperature is raised to WAT + 54 % the deposit underwent 100 % removal, while increasing it to WAT + 12 % resulted in 97 % removal throughout the experiment. Raising the removal temperature to WAT − 7 % resulted in no removal.A mechanism for thermal removal is proposed based on visual evidence for a counter-diffusion process preceding detachment. During removal, the deposit becomes less dense with wax crystals over time, lowering its yield stress until a point where shear forces from the flow can strip and carry away large chunks of wax deposit. Higher removal temperatures require less time for detachment to occur. Increasing the coolant temperature to WAT + 54 % required only 8 min for detachment to occur, while increasing it to WAT + 12 % extended this time to 46 min. Deposit yield stress and fluid shear stresses are used to determine the minimum removal temperature for active heating. The pipe wall needs to be raised at least to this temperature for removal to occur. The higher the wall temperature is raised above this value, the faster the removal will occur. Understanding this mechanism can inform the development of accurate removal models and improve production economics.