The influence of pressure and dissolved gases in petroleum on the efficiency of wax deposition inhibitors

Lenise Vieira, Maria Buchuid and Elizabete Lucas
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Evaluations of wax inhibitors carried out in laboratories are generally performed on stabilized oil samples, that is, without the presence of natural gas and at atmospheric pressure. Therefore, the effects of two important factors that influence wax solubility – the light fractions and temperature – are not considered, and the results may not reflect what really happens in production lines and facilities. This work evaluates the efficiency of two wax inhibitors based on ethylene copolymer and vinyl acetate, at four concentrations, in a sample of paraffinic oil in the presence of light fractions and under pressure. The parameter employed in the evaluation was the wax appearance temperature (WAT), or the cloud point, determined by high-pressure differential scanning calorimetry. The gas used was a mixture of eight components and the tests were run at three pressures. In general, the inhibitors had little influence on the cloud point and a pronounced effect on the pour point and viscosity. In this case it was possible to observe changes in the WAT with both wax inhibitors in the tests conducted at atmospheric pressure up to 150 bar and in the presence of the multi-component gas mixture, suggesting that one of the mechanisms through which wax deposition inhibitors work is polynucleation.

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