|Institution:||Colorado School of Mines|
|Keywords:||Flowloop; Rheology; Methane Hydrates; Emulsion|
|Full text PDF:||http://hdl.handle.net/11124/20172|
In this doctoral work, the viscosity and transportability of gas hydrate slurries were investigated using a high pressure rheometer and an industrial-scale high pressure flowloop. A model water-in-oil emulsion was developed specifically for this study and consists of mineral oil (350T and 70T), a surfactant mixture (sorbitane monooleate, Span 80 and Aerosol OT, AOT) and de-ionized water. The water volume fraction (water cut) that will form a stable water-in-oil emulsion depends on the type of mineral oil used. Mineral oil 70T can form a stable emulsion for water cuts in the range of 10 – 70 vol.% water, while mineral oil 350T can form a stable emulsion for water cuts in the range of 10 – 40 vol.% water. Characterization tests were conducted on these model emulsions, and the results show that the emulsions are relatively stable (no phase separation, sedimentation and coalescence) for a period of one week. In addition, the average water droplet size was determined to be in the range of 2 – 5 μm. Finally, high pressure autoclave tests were conducted using the model emulsions, and showed that the emulsions have similar properties (i.e. relation of motor current versus hydrate volume fraction) to that of water-in-crude oil emulsions. In order to understand the effect of hydrate particles on the viscosity of the system, viscosity measurements of the emulsions (prior gas hydrate formation) were conducted at various temperatures, pressures and water cuts. A generalized equation that is a function of temperature, water volume fraction and saturation of the oil phase was developed. This generalized equation is able to predict the viscosity of the emulsion fairly accurately (within ± 13%) at low temperature (≤ 10 °C). In-situ gas hydrate formation and hydrate slurries viscosity measurements were also performed in this work. Measurements were made using a high pressure rheometer connected to a high pressure ISCO pump. A four-blades vane impeller was used to mix the slurries. Experiments were conducted using the two model emulsions that were developed in this work. Viscosity measurements were conducted at a constant temperature of 1 °C, constant pressure of 1500 psig and constant mixing speed of 477 RPM. The water cut was set to be between 5 – 30 vol.% water. In addition, for mineral oil 70T emulsions, experiments were also performed near the emulsion inversion point. The results of this work shows that the relative viscosity of gas hydrate slurries can be modeled as a function of the hydrate volume fraction of the systems. In addition, emulsion breaking after hydrate formation was observed for hydrate slurries tests near the emulsion inversion points. Next, gas hydrate transportability was also investigated in an industrial-scale flowloop. Investigations were made at two different flow conditions (fully dispersed and partially dispersed systems). The different flow conditions were achieved by changing the water cut, as well as the flowloop pump speed (fluid mixture velocity). Results of the tests shows that the relative… Advisors/Committee Members: Koh, Carolyn A. (Carolyn Ann) (advisor), Wu, David T. (advisor), Wu, Ning (committee member), Maupin, C. Mark (committee member), Yin, Xiaolong (committee member).