Formation condition data for methane hydrate in ammonia + water and ammonia + water + tetrahydrofunan (THF) systems are very important for the process development and the determination of operation condition for recycling the vent gas of ammonia synthesis using hydrates. This paper focused on the formation conditions of methane hydrate in the presence of NH3 + H2O and NH3 + H2O + THF system. Equilibrium data of methane hydrate in the temperature, pressure and concentration ranges from 277 to 291 K, 0 to 8 MPa, 1 to 5 % ammonia, were obtained. The experimental results indicate that ammonia has an inhibitive effect on hydrate formation. The higher the concentration of ammonia is, the higher the formation pressure for methane hydrate will be.

Recently, carbon dioxide injection into deep sea sediments has become one of the carbon dioxide mitigation methods since carbon dioxide hydrates are stable at the prevailing pressure and temperature conditions. The Black Sea, which is one of the major identified natural methane hydrate regions of the world, can be a good candidate for carbon dioxide storage in hydrate form. Injected carbon dioxide under the methane hydrate stability region will be in contact with methane hydrate which should be analyzed thoroughly in order to increase our understanding on the gaseous carbon dioxide and methane hydrate interaction. For the storage of huge amounts of CO2, geological structure must contain an impermeable barrier. In general such a barrier may consist of clay or salt. In this study, sealing efficiency of methane hydrate and long term fate of the CO2 disposal under the methane hydrate zone is investigated. In order to determine the interaction of CO2 and CH4 hydrate and the sealing efficiency of CH4 hydrate, experimental setup is prepared and various tests are performed including the CH4 hydrate formation in both bulk conditions and within sand particles, measurement of the permeability of unconsolidated sand particles that includes 30% and 50% methane hydrate saturations and injection of CO2 into the CH4 hydrate. Results of the experiments indicate that, presence of hydrate sharply decreases the permeability of the unconsolidated sand system and systems with hydrate saturations greater than 50% may act as an impermeable layer. Also, CO2-CH4 swap within the hydrate cages is observed at different experimental conditions. As a result of this study, it can be concluded that methane hydrate stability region in deep sea sediments would be a good alternative for the safe storage of CO2. Therefore, methane hydrate stability region in the Black Sea sediments can be considered for the disposal of CO2.

Downhole acoustic data were acquired in very low-velocity, hydrate-bearing formations at five sites drilled on the Cascadia Margin during the Integrated Ocean Drilling Program (IODP) Expedition 311. P-wave velocity in marine sediments typically increases with depth as porosity decreases because of compaction. In general, Vp increases from ~1.6 at the seafloor to ~2.0 km/s ~300 m below seafloor at these sites. Gas hydrate-bearing intervals appear as high-velocity anomalies over this trend because solid hydrates stiffen the sediment. Logging-while-drilling (LWD) sonic technology, however, is challenged to recover accurate P-wave velocity in shallow sediments where velocities are low and approach the fluid velocity. Low formation Vp make the analysis of LWD sonic data difficult because of the strong effects of leaky-P wave modes, which typically have high amplitudes and are dispersive. We examine the frequency dispersion of borehole leaky-P modes and establish a minimum depth (approx 50-100 m) below the seafloor at each site where Vp can be accurately estimated using LWD data. Below this depth, Vp estimates from LWD sonic data compare well with wireline sonic logs and VSP interval velocities in nearby holes, but differ in detail due to local heterogeneity. We derive hydrate saturation using published models and the best estimate of Vp at these sites and compare results with independent resistivity-derived saturations.