There are massive quantities of gas hydrates in permafrost regions 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 appropriate economical conditions. Furthermore, these gas hydrates are a hazard to drilling operations, as they could become unstable under typical wellbore conditions and release large quantities of gas. Decomposition of natural gas hydrates in porous media could also be responsible for subsea landslides and global weather changes. Recent studies show that they might provide an opportunity for CO2 sequestering.
Hydrate phase boundary in porous media is known to be a function of many factors, such as pore size, fluid saturation, in situ stresses, and sediment mineralogy. Deviations, as large as 100 meters, have been observed between measured and predicted hydrate stability zones in marine sediments. Laboratory efforts in measuring gas hydrate stability zone in porous media have concentrated on the effect of pore size and fluid saturation. However, there are considerable deviations and inconsistencies in the reported data.
This paper presents an experimental set-up, test procedures, and some of the results obtained on porous glass beads with 306 Å and 158 Å pore sizes with methane and CO2. The test procedure is based on step-heating as compared to continuous heating, used by many laboratories. The results proved that step-heating technique, as used in this laboratory, could provide reliable and consistent data on measuring hydrate phase boundary in porous media, without compromising on the 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 and that of bulk conditions. These results are important in estimating the hydrate stability zones in porous media, as indicated by BSR in seismic surveys.
