(252c) Providing Guidelines for Thermal Removal of Paraffin Deposits from Production Lines

Wax deposition in subsea crude oil pipelines is a major operational issue in oil production and transportation. Several methods are used in the prevention and remediation of wax deposition, including pigging, chemical inhibition, thermal insulation, and active heating. Active heating involves using a heating medium or electrical current to heat the wall of the pipe carrying the production fluid and is increasingly used as a cost-effective strategy for controlling wax deposition in offshore flowlines. While these techniques have been widely used, 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 finding actual temperature targets for wax removal. If these can be defined and current operational targets are lowered, this will reduce energy requirements and therefore reduce costs. 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.

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. A method for determining the minimum temperature of removal is proposed based on this mechanism and validated using yield stress correlations based on an in-depth rheological study of waxy oils. 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.