Pipeline blockage by clathrate hydrate formation is a major problem encountered in the oil and gas industry. Hydrate induced plug formation causes product flow interruption, severe equipment damage, environmental pollution and personnel fatalities. In order to efficiently and economically prevent hydrate formation, understanding of the underlying physical principles leading to hydrate blockage is required. This work addresses correlation of rheological properties of cyclopentane hydrate-forming emulsions with thermodynamics, nucleation by ice and morphology. Cyclopentane, used as hydrate-former in the model emulsion under atmospheric conditions, forms the same natural gas hydrate structure found in the oil and gas industry. The effect of aqueous phase salinity on density-matched 40% (v/v) hydrate-forming emulsion are reported. Using micro-differential scanning calorimetry and rheometry, a correlation of the rheological properties to thermodynamic driving forces is obtained. Rheological properties, including the viscosity evolution time, final viscosity and its shear rate dependence are determined; the material viscosity increases markedly as hydrate forms. The viscosity evolution time is smaller at lower temperature, i.e., at higher subcooling relative to the hydrate equilibrium dissociation temperature. Maximum viscosity is attained when the thermodynamic water to hydrate conversion is 60-80%; this is attributed to capillary bridges. The effects of heterogeneous nucleation of cyclopentane hydrate by ice on the morphological properties of hydrate formed on a single aqueous drop immersed in cyclopentane and the rheological properties of density-matched 40% (v/v) aqueous fraction hydrate-forming emulsions are also reported. Experimental observations indicate that the ice-oil-aqueous phase contact line is the hydrate heterogeneous nucleation site. The viscosity of a metastable hydrate-forming emulsion evolves rapidly when the emulsion is seeded with ice, although more slowly than when seeded with the hydrate itself. A comparison of cyclopentane hydrate- and ice-forming emulsions is reported. Large differences in viscosity were observed between the hydrate- and ice-forming emulsions; ice-forming emulsion viscosity was lower than hydrate-forming emulsion at similar subcoolings and water conversions. Morphological results show that the hydrate seed surface punctures the drop in the hydrate-forming emulsion, consequently as the drop wets the seed, hydrate is formed; whereas in the ice-forming emulsion, the whole water drop freezes as a bulk and its spherical shape is retained. These observations indicate that the ice-forming emulsions do not capture the rheological properties and mechanism of morphology evolution of hydrate-forming emulsions.
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|Advisor:||Morris, Jeffrey F.|
|Commitee:||Blanford, William J., Couzis, Alexander, Maldarelli, Charles, Subramani, Hariprasad J.|
|School:||The City College of New York|
|School Location:||United States -- New York|
|Source:||DAI-B 76/06(E), Dissertation Abstracts International|
|Keywords:||Clathrate hydrate, Emulsion, Flow assurance, Heterogeneous nucleation, Salt, Thermodynamics|
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