Influence of pour point depressants (PPDs) on wax deposition: A study on wax deposit characteristics and pipeline pigging

Pour point depressant (PPD) is widely used for wax prevention in crude oil production and transportation. This paper aims to investigate the compositional and rheological properties of wax deposits formed from crude oils with and without PPDs. To this end, an in-house cylindrical Taylor-Couette cold finger device was constructed to conduct wax deposition experiments. Tests on wax deposits show that wax deposit properties are dramatically changed by addition of PPDs. It was observed that PPDs lower wax deposition rate and increase wax appearance temperature (WAT) and wax content of the deposits. Moreover, the enriched heavy components of n-alkanes and the diluted light ones indicate an accelerated aging process caused by PPDs, and the critical carbon number (CCN) and average carbon number of the deposits accordingly increase. The contents of asphaltenes and resins entrained in wax deposits get lowered when PPD was added into the crude oil. In addition, PPDs would weaken the mechanical strength of wax deposits, thus the wax resistive force decreases and therefore the risk of pig stalling accordingly gets lowered. Above all, among the evaluated PPDs, NPPD (which contains nanocomposites) presents the best wax inhibition performance.