(72c) Characterization of Gas Hydrate Slurry Viscosity Using a High Pressure Rheometer

Characterization
of Gas Hydrate Slurry Viscosity Using a High Pressure Rheometer

Ahmad
AA Majid^1,2, David T Wu^1,3 ,Carolyn
A Koh^1*

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.