Institute of Petroleum Engineering

Centre for Gas Hydrate Research Publications

Abstract 048
Gas Hydrates in the Porous Media
Llamedo, M., Tohidi, B., Østergaard, K.K., and Burgass, R.W.
EAGE 8th Annual Research Review, Edinburgh, UK, 16 February (2000).
Gas Hydrates are crystalline components of water that belong to a group of solids called clathrates. They are formed from mixtures of water and low molar mass gases at high pressures and low temperatures. Gas hydrates are known to occur in one of the three crystalline structures (i.e., structure I, II, and H). In the petroleum industry, it is desirable to avoid the formation of gas hydrates, as they tend to agglomerate and block pipelines and process equipment. However, naturally occurring gas hydrates that form in the permafrost region or in Deep Ocean represent a vast untouched natural gas reserve. The current estimates show that the amount of energy trapped in the gas hydrates is twice total fossil fuels. The huge size of gas hydrate deposits may have an important environmental implication due to the fact that methane is a greenhouse gas and can have a positive feedback mechanism for global warming. Also there are schemes, suggesting the disposal of CO2 in the form of gas hydrates in porous media. There are strong evidences that destabilised gas hydrates beneath the sea floor leads to geological hazards such as submarine mass movements, which among other consequences could give rise to a hazard in subsea communication cables, pipeline and wells. Most geologists believe that gas hydrates played an important role in the history of earth and glacial ages, having a buffering effect in the sudden changes of temperature and preserving life on this planet. In onshore drilling, except in polar and permafrost region, there is little possibility of drilling through hydrate region. However, in the offshore drilling, in particular higher water depths, there is possibility of encountering hydrate-bearing sediments. These hydrates in subsea sediments and the free gas below hydrate stability zone are a safety hazard to drilling operations. There is very little information on the physics of hydrate formation and decomposition in porous media. Therefore all kinetic and thermodynamic models are based on measuring external parameters and hypothetical assumptions or the available data on ice. Considering the ever increasing importance of gas hydrates and their role in drilling, geology and their significance as a potential source of energy, it crucial to gain a better understanding of their formation and decomposition in porous media. A two-year research programme has started at Heriot-Watt University, investigating the phase behaviour of gas hydrates in porous media. This paper presents the experimental set-up and some of the results obtained on controlled-pore-glass with 251Å and 128Å pore sizes. The results of the tests with different water saturations are also presented. The data showed that there could be a significant difference between the hydrate free zone of gas hydrates in porous media to that of bulk conditions. These results are important in estimating the hydrate stability zones in porous media, as indicated by BSR in seismic surveys. Further work is planned to investigate the effect of other important variables and the kinetics of gas hydrate formation and decomposition in porous media.