Tohidi, Bahman¹, Ben Clennell², Ross Anderson¹, Jinhai Yang¹ 
(1) Heriot-Watt University, Edinburgh, United Kingdom 
(2) CSIRO Petroleum Division, Perth, Australia

ABSTRACT: Gas Hydrates Studies Using High Pressure Glass Micromodels

Glass micromodels provide a unique opportunity for the observation of phase behaviour in reservoir fluid systems. This technique has been used to study hydrates in porous media. Such observations can contribute significantly to our understanding of the mechanism of gas hydrate formation and their distribution within sediments. 
Here we present details of a glass micromodel set-up for the visual observation of gas hydrate formation and dissociation in porous media. Several series of tests have been conducted with C1, CO2, a mixtures of C1/CO2, and a natural gas to investigate the effect of fluid composition, presence or absence of free gas and the presence of nucleation sites on gas hydrate formation in porous media, as well as the effect of salt on the mechanism of gas hydrate formation. 
The results show that gas hydrates could be formed at the gas water interface or from the dissolved gas within the water phase, whereas the amount of hydrates formed in the water phase is a function of gas solubility. It is demonstrated that the formation of gas hydrates reduces gas saturation in the adjacent water phase, resulting in a concentration gradient and gas diffusion from the surrounding water. Gas diffusion plays an important role in gas hydrate growth, in particular at low degrees of subcooling, where some gas bubbles are dissolved in the water phase and transported to the hydrate forming regions. This may explain the presence or absence of free gas (i.e., BSR) below the hydrate stability zone. The presence of salts, and their transportation from the hydrate forming region, can have a significant effect on gas hydrate growth.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.