Institute of Petroleum Engineering

Centre for Gas Hydrate Research Publications

Abstract 049
Measuring Hydrate Phase Boundary in Porous Media
Tohidi, B., Østergaard, K.K., Llamedo, M., and Burgass, R.W.
6th International Conference Gas in Marine Sediments, St Petersburg, Russia, 5-9 September (2000).
There are enormous amounts of gas hydrates in permafrost region and deep sea sediments. The current estimates show that the amount of energy in these gas hydrates is twice total fossil fuel reserves, indicating a huge source of energy, which can be exploited in the right economical conditions. Furthermore, these gas hydrates are a safety hazard to drilling operation, as they could become unstable under typical wellbore conditions and produce large quantities of gas. The decomposition of natural gas hydrates in porous media could also be responsible for subsea land slides and global weather changes. Recent studies show that they might provide an opportunity for CO2 sequestering. There is very little information on the physics of hydrate formation and decomposition in porous media. Therefore kinetic and thermodynamic models are mainly based on measuring external parameters and hypothetical assumptions or the available data on ice. Considering the ever-increasing importance of gas hydrates in sediments, it crucial to gain a better understanding of their formation and decomposition in porous media. Perhaps the first step is to develop test methods in generating reliable experimental data on the hydrate phase boundary of various gases in porous media as well as simulating natural environment in the laboratory. A two-year research programme has started at Heriot-Watt University, investigating the phase behaviour of gas hydrates in porous media. This paper presents an experimental set-up, test procedures, and some of the results obtained on porous glass beads with 251 Å and 128 Å pore sizes with methane and CO2. The set of data on CO2 is unique and has not been reported in the literature before. The results proved that step-heating technique used in this laboratory could provide reliable and consistent data on measuring hydrate phase boundary in bulk and porous media, while reducing time and cost of experiments. 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.