Paraffin Deposition in Production Lines: Effect of Operating Parameters on Deposition Characteristics
Aziz Alhejaili, Elijah Bell, Nagu Daraboina
Abstract
Wax deposition in subsea crude oil pipelines remains one of the major operational issues in oil production. Environmental and operational conditions have a massive impact on how much wax forms and the deposit characteristics. Model oil with a wide range of carbon number distributions was prepared to imitate crude behavior. A newly designed flow loop was used to investigate the impact of the deposition time, flow rate, and pipe wall temperature on wax deposition characteristics. It was found that increasing the deposition time led to increases in deposit thickness, wax content, wax appearance temperature (WAT), wax disappearance temperature (WDT), and viscosity. As expected, as flow rates increased, deposit thickness decreased due to shear. Comparing 24 h deposition times showed that there was not a direct correlation between the two, as increasing Reynolds number from 4500 to 8500 resulted in a 0.57 mm reduction in thickness while an increase from 8500 to 12,500 resulted in only a 0.13 mm reduction. While the thickness decreased, significant increases were observed in the wax content, WAT, and WDT of the deposit. Computational fluid dynamics (CFD) simulations are used to describe the impact that flow rate has on heat transfer between the oil and the cold environment. Lower flow rates allow for more heat transfer to occur, aiding in the deposition process and leading to more thickness. The detailed investigation of wax deposition characteristics presented here will aid operators in designing better mitigation strategies under the given conditions.