Characterization of Gas Hydrate Slurry Viscosity Using a High Pressure Rheometer
Ahmad AA Majid1,2, David T Wu1,3 ,Carolyn A Koh1*
1. Center for Hydrate Research, Colorado School of Mines, Golden CO 80401, USA
2. Faculty of Chemical & Natural Resources Engineering, Universiti Malaysia Pahang, Malaysia
3. Department of Chemistry, Colorado School of Mines, Golden CO 80401, USA
ABSTRACT
Gas hydrates are solid structures that contain small gas molecules (e.g. methane, ethane, propane, xenon) trapped inside molecular water cages. Hydrates typically form at high pressure and low temperature. As such, hydrates can form and plug oil and gas flowlines, and are therefore a major concern to the oil and gas industry. In this work, we performed in-situ gas hydrate slurry viscosity measurements using a high pressure rheometer. Measurements were performed using both a model emulsion and a crude oil emulsion as a function of water content, gas composition, subcooling (i.e., temperature and pressure) and shear rate. Measurements were conducted systematically in order to evaluate the effect of each variable on the viscosity of the system. Based on this work, we developed a model for relative viscosity as a function of the oil properties and hydrate volume fraction. Furthermore, initial investigations show that the viscosity profiles are significantly affected by the crystal structure (sI or sII) of the hydrate. It was also observed that the conversion of water to hydrate has a significant role on the agglomeration of hydrate particles in the system; whereby it is hypothesized that the presence of a free water layer may lead to significant agglomeration of hydrate particles. Comparisons between model and crude oil emulsion systems suggest that the natural surfactants in crude oil may help in preventing the agglomeration of hydrate particles.
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