Bjørn Kvamme
University of Bergen, Norway
Title: Impact of H2S content on thermodynamic stability of hydrate formed from CO2/N2 mixtures
Biography
Biography: Bjørn Kvamme
Abstract
The total global energy of CH4 trapped in crystalline form as hydrates is huge and may exceed twice the amount of energy of known sources of conventional fossil fuels. Most of the natural gas hydrates found in nature are from biological degradation of organic material in the upper few hundred meters and correspondingly high purity of CH4. These hydrates forms structure I hydrate, which contains a ratio of 1:3 of small to large cavities. The small cavity is very well stabilized by CH4 while CO2 fits the largest cavity better, and the water is having stronger short range interactions with CO2 than CH4. CO2 gas or liquid that is brought in contact with CH4 hydrate will therefore replace the CH4 in most of the large cavities. This is possible through two mechanisms, a solid state direct conversion and a second mechanism in which CO2 form a new hydrate with free pore water. The released heat from this hydrate formation assists in dissociating the in situ CH4 hydrate. Substantial amounts of N2 (often as high as 80% by volume) is proposed as one solution for reduced hydrate plugging and increased gas permeability. In this study we examine the minimum limits of CO2 content for ability to form new hydrate from liquid water and injected gas, and also how this changes with small impurities of H2S. It is found that even as small amounts of H2S as 1% can substantially increase the ability of injection gas to form new hydrate, as compared to same mixture without H2S.