In this study, a deposition model called the Michigan Wax Predictor (MWP) was used to establish criteria as to whether the rate of wax deposition increases or decreases as the oil/coolant temperature is changed in a series of flow-loop experiments. The model was able to predict the effects of the temperature conditions on wax deposition without applying any adjustable parameters. Despite the fact that many previous studies have used the "thermal driving force" to characterize the effect of temperature on wax deposition, it was not the most comprehensive predictive parameter, as it neglects the importance of the solubility curve on wax deposition. This study has revealed that the most important factors affecting deposition are the mass driving force and the shape of the solubility curve. The major impact of the shape of the solubility curve is to affect the change in characteristic mass flux for wax deposition the when the oil and the coolant temperatures are changed. In particular, the differences in the shapes of the solubility curve can be used to explain the discrepancies on the effect of the oil temperature on wax deposition observed in different deposition studies.

We report for the first time the results from a systematic investigation of how asphaltenes of different polarity affect crystallization and gelation of waxy oils. The more polar asphaltenes were found to be more aromatic in nature and more highly self-aggregated in the solvent. The presence of less polar asphaltenes in the waxy oil reduced the wax appearance temperature and wax precipitation to a greater degree compared to more polar asphaltenes, which was mainly attributed to the difference in the aggregation state of asphaltenes of different polarity. Reducing the polarity of asphaltenes present in the oil also resulted in a lower gelation temperature, lower storage modulus, and lower yield stress, which was probably because the less polar asphaltenes were more similar to wax on the molecular level and, thus, more readily interacting with wax. Notably, a 99% reduction in the yield stress was observed upon the addition of the least polar asphaltenes examined in the present work, in contrast to the 62% yield stress reduction upon the addition of the most polar asphaltenes. This observation may be of industrial significance because it suggests that the crude oil containing less polar asphaltenes may form a softer gel or deposit that is more easily broken or removed. Microscopic analysis showed that the wax crystals precipitated in the presence of less polar asphaltenes have a smaller aspect ratio.

We report results from a systematic investigation of the effect of the temperature on the wettability of oil/brine/rock systems. An oil sample, produced from a sandstone reservoir, was tested on sandstone-like substrates (i.e., mica and quartz) in NaCl and MgCl2 solutions with concentrations ranging from 0 to 3 M. Raising the temperature from 25 to 50 °C has no discernible effect on the contact angle, regardless of substrate type, brine type, or salt concentration. Another oil sample, obtained from a carbonate reservoir, was examined on carbonate-like substrates (i.e., calcite) in NaCl and MgCl2 solutions over a concentration range of 0–1 M. The contact angles decrease as the temperature increases from 25 to 65 °C, and this temperature effect also strongly depends upon the brine type and salt concentration. A systematic examination of the ζ potential of rock/brine and oil/brine interfaces under different conditions and subsequent discussions indicate that contact angle and ζ potential may not be directly linked. These findings regarding the wettability of oil/brine/rock systems may improve the understanding of low-salinity wateflooding mechanisms by elucidating the combined effects of the temperature and other critical variables, including brine type, brine concentration, crude oil composition, and substrate type.

The experimental trend of a reduced deposit with an increasing flow rate has been observed in a series of wax studies. Despite the fact that many previous studies intuitively attribute the reason to the "shear removal", the role of heat and mass transfer was frequently overlooked as the true explanation. In the current study, the Michigan Wax Predictor (MWP) was applied to elucidate this trend by analyzing the growth rate of the wax deposit in a series of flowloop experiments from first principles. The model was able to predict the experimentally observed decrease in deposit thickness with an increasing oil flow rate without any adjustable parameters. It was found that three effects exist to affect wax deposition when the oil flow rate is changed, and each one can either increase or decrease the growth rate of the deposit. These effects focus on the heat-and masstransfer phenomena at the oil−deposit interface. In addition, this study also revealed that the dynamics of the competition between all of these three effects can vary as time progresses and that the overall behavior of the wax deposit growth is eventually determined by the most dominant effect of the three. These results have provided important insight for the effects of the oil flow rate on wax deposition.

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