Asphaltene deposition in transparent mini- and microchannels

  • Yougong Zhuang

Student thesis: Master's Thesis

Abstract

In the process of oil production, transportation and refinery, asphaltene deposition is a recurring problem, especially for wide utilization of enhanced oil recovery (EOR) technologies. Deposition of precipitated asphaltene particles can cause formation damage in reservoirs, blockage in wellbores or even problem in separators, pumps, pipelines, heat exchangers and various equipment. To solve this problem, remediation and prevention are two ways. Remediation is to remove deposits from the formation and production facilities via solvents such as xylene or toluene. However, these ways of remediation are costly and environmentally harmful. Post-processes of cleansing are also another difficulties. Therefore, many studies focus on the prevention of asphaltene deposition by understanding the mechanism of asphaltene deposition. This study focuses on the experimental investigation of asphaltene deposition in miniand micro- channels. Heptane-induced asphaltene precipitation is utilized to precipitate dissolved asphaltene particles in crude oil to form asphaltene particles in ambient temperature and standard atmospheric pressure. These asphaltene particles deposit gradually on the surface of mini- and micro- channel. The key parameters that influence the mechanism of asphaltene deposition are flow rate, the ratio of heptane to crude oil, oil type, channel configuration (horizontal or vertical), injection direction (top or bottom) and channel size. Measurements of asphaltene deposition were carried out in mini- and micro- channels using several techniques. These techniques include deposit thickness measurement using a 3D digital microscope, image analysis for deposit quantifications using a microscope system and weight measurement via an electronic balance. In this study, a new method of measurement based on normalized light absorption is developed to quantify asphaltene deposits. Thickness of asphaltene deposits can be measured by a 3D digital microscope. The correlation between normalized light absorption and deposition thickness was investigated. It is confirmed that this correlation equation is validated based on the comparison between measured thickness and calculated thickness. It was observed that asphaltene deposition process might follow three stages, (i) small asphaltene particle deposition at the beginning of the experiment, (ii) a rapid and continuous deposition increase after few hours and (iii) a decrease on deposition rate in the system at the end of the experimentation. Key parameters on asphaltene precipitation and deposition were investigated and reported. It is observed that asphaltene precipitation onset is located in the range of 50% to 55% n-heptane concentration for SB crude oil and 35% to 40% for SA crude oil. Deposition using centrifuged oil is higher than that using neat oil. The generation of asphaltene deposition is mainly due to small size asphaltene particles since the existing large asphaltene aggregates in the neat oil do not tend to deposit. Asphaltene aggregation size effect was studied using 5.0 μm and 0.45 μm filtered oil. It is observed that the number of asphaltene particles using 5.0 μm filtered oil is higher than that using 0.45 μm filtered oil. However, the quantity is too small to be measured. The influence of flow rate on deposition was studied. It is observed that more deposits are created by lower flow rate. Injection volume of asphaltene has a significant effect on deposition compared to the experimental flow rate range (0.00075 ml/min to 0.00375 ml/min for mini-channel and 0.003 to 0.008 ml/min for microchannel). A critical shear rate is obtained to distinguish diffusion-controlled regime and shear limited regime in minichannel experiments. Furthermore, a relation between normalized light absorption and shear rate is attained in the shear limited regime. It is observed that asphaltene deposits along the longitudinal direction of channels are non-uniform. Deposition decreases with the increasing of the longitudinal distance from the inlet. This non-uniform deposition distribution is mainly due to local mass transport limitations and asphaltene aggregation size effect. These studies provide useful information on behavior of asphaltene precipitation and deposition in diverse setting conditions and are in particular help in developing and validating numerical model.
Date of Award2015
Original languageAmerican English
SupervisorAfshin Goharzadeh (Supervisor)

Keywords

  • Applied sciences
  • Mechanical engineering
  • 0548:Mechanical engineering

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