Mitigating Wax Deposition From Crude Oils: Correlations Between Physical-Chemical Properties of Crude Oils and the Performance of Wax Inhibitors

Abstract

In this paper, we explore the correlations between the effectiveness of several wax inhibitors and physico-chemical properties of crude oils. First, the effects of the type of fluid was studied by dissolving refined paraffin waxes in non-waxy crude oils-here termed ЉdoctoredЉ crude oils-of different properties and comparing the wax appearance temperature and pour point of the doctored crude oils to those determined for a model waxy fluid used in previous studies [1]. After treating the doctored crude oils with wax inhibitors, the ability of the chemicals to depress pour point was examined. Even though the paraffin waxes in these fluids were exactly the same, marked differences in the effectiveness of the chemicals were observed. The doctored condensate was very responsive to the inhibitors in a similar manner to that observed for the model waxy fluid, while doctored crude oils from the Middle East showed a significantly reduced response to most inhibitors. The results are discussed in terms of the differences in solubility of the paraffin waxes, and the chemical composition of the crude oils.Secondly, the influence of a wide range of crude oil properties on the effectiveness of wax inhibitors was investigated by treating seven (7) crude oils of different geographical origin with five (5) wax inhibitors and evaluating their performance to reduce wax deposits in a cold finger experiments. Distinct crude oil behaviors were observed in terms of their responsiveness to the wax inhibitors. Some crude oils were equally responsive to wax inhibitors, while others showed moderate response, and one was not responsive at all. The results are clear examples of the crude oil ЉspecificityЉ, and demonstrate the risks of using model waxy fluids, or even different crude oils, to extrapolate the performance of wax inhibitors. Additives that worked well in model fluids might not work at all in real crude oils.Lastly, physical properties of crude oils and molecular characteristics derived from high-temperature gas chromatography (HTGC) were used to seek a correlation to wax inhibition performance using chemometrics tools, specifically, principal component analysis (PCA). Preliminary results from the PCA approach indicate that several crude oil properties affect inhibition efficiency. The analysis suggests that the efficiency of the inhibitors studied here increases for crude oils with lower wax appearance temperature, lower pour point and lower carbon number distribution. It could also be inferred that inhibition efficiency was improved in crude oils containing higher amounts of asphaltenes but low wax content.

Evaluation of Wax Inhibitor Performance through Various Techniques

“…The DSC results show that this wax consists of alkanes in the region around n -C40. This is consistent with other’s work that showed that wax inhibitors are less effective for waxes that have a carbon number greater than about C25. ,,,,, This suggests that WIA may not contain long enough aliphatic chains to adequately interact with the larger n -paraffins to cocrystallize with them. , …”

“…Since the HTGC work shows that the centrifuged waxes are enriched in >C28 n -paraffins, and considering that the WD Waxy B material is also enriched in the centrifuged waxes, then the WD Waxy B must also be likewise enriched in larger n -paraffinsor associated n -paraffin structuresof about C28 or larger. These results show that the WD is a convenient way to differentiate between crude oils that have more >C25 n -paraffins which are known to be difficult to treat with wax inhibitors . The data also show that the asphaltenes from the Minnelusa crude oil do not precipitate with, or are concentrated in, the centrifuged waxes.…”

“…By using a chemomechanical approach, it was determined that wax inhibitor efficiency was generally lower for heavier crudes and likewise for crudes with higher boiling points, WAT, pour point, aromatics content, and higher amounts of >C25 n -paraffins. Conversely, inhibitor performance improved for crude oils with higher amounts of asphaltenes, resins, total acid number, and lower amounts of >C25 n -paraffins . Several others have also observed that wax inhibitor efficiency significantly decreases as the amount of the >C25 n -paraffins increases − or in some cases as the n -paraffins become >C34. , The most effective inhibitors should seek to target these heavier n -paraffins which are most problematic because they become concentrated in waxy deposits. , It has also been reported that a higher concentration of iso- and cyclo-paraffins can have a synergistic effect to increase paraffin dispersant effectiveness …”

“…Significant steps have been made in this direction through studies focused on understanding the interplays between different types of waxes and the various crude oil components and how these interactions influence the morphology and structure of wax crystal formation. Recently a physicochemical approach was applied to determine which crude oil properties are most significant for predicting the performance of several different wax inhibitors . This was done by doping different nonwaxy crude oils with refined paraffin waxes and treating them with various additives.…”

“…Recently a physicochemical approach was applied to determine which crude oil properties are most significant for predicting the performance of several different wax inhibitors. 17 This was done by doping different nonwaxy crude oils with refined paraffin waxes and treating them with various additives. By using a chemomechanical approach, it was determined that wax inhibitor efficiency was generally lower for heavier crudes and likewise for crudes with higher boiling points, WAT, pour point, aromatics content, and higher amounts of >C25 n-paraffins.…”