Influence Of Fine Sediment Particle Size And Pore Water Salinity On The Stable P-T Condition Of Methane Hydrate

Natural gas hydrate (NGH), which extensively exists in the sediment, will be inevitably influenced by sediment characteristics. More and more researches have been done about how sediment characteristics influence the formation of NGH, but it's still too far to totally understand the formation mechanism of NGH in sediments due to its complexity. To identify the distribution and make clear of its reserves, stable pressure and temperature (P-T) conditions of NGH must be plotted. In the past decades, some experiments about how sediment particle size?different type of purous media and pore water salinity affect the stability condition of NGH have been done. However, the data of phase equilibrium of NGH in porous media are still not enough, especially in fine grained sediment, which electrolyte solution is filled in sediment pores as pore water. To make up it's deficiency, we used quartz sand of four particle sizes(2.5?m?10?m?45.7?m and 158.5?m)in a constant volume reactor, and pure methane gas(in order to reduce the complexity of the experiment). The method of stepwise temperature rising was used to get stable P-T conditions of methane hydrate in pore water with different salinity(w (NaCl)=0%?1.0%.3.5%?.0%?10.0% and 15.0%). So that we can get the effect of particle size and pore water salinity on the stable P-T conditions of methane hydrate. Furthermore, we select quartz sand of 45.7 ?m, mixed with w (clay)=2%?5% and 20% (clay were sodium montmorillonite, kaolin and bentonite), with pure water saturated, to get the effect of different porous media on phase equilibrium condition of methane hydrate.From the data, we got the following conclusions:1.Compared with free medium the P-T conditions of methane hydrate in fine quartz sand become harder, and the equilibrium curve of methane hydrate moves to the left with the decrease of particle size. But in coarse quartz sand, the P-T conditions of methane hydrate barely changed;2. With the existence of porous media, the equilibrium conditions of methane hydrate still follows the conclusion that with increase of pore water salinity, the equilibrium curve moves toward the direction of high pressure and low temperature; Pore water salinity effect and porous media effect on methane hydrate superposed, so different particle size curve between the gap is obvious in high pore water salinity;3.The stable P-T conditions of methane hydrate were obtained for the first time, and the change of montmorillonite content has little effect on the phase equilibrium conditions of methane hydrate.