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

Abstract

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 "doctored" 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 "specificity", 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.