Gas hydrate formation from two types of dissolved gas (methane and mixed gas) was studied under varying thermodynamic conditions in a novel apparatus containing two different natural media from the South China Sea. Th...Gas hydrate formation from two types of dissolved gas (methane and mixed gas) was studied under varying thermodynamic conditions in a novel apparatus containing two different natural media from the South China Sea. The testing media consisted of silica sand particles with diameters of 150-250 μm and 250-380 μm. Hydrate was formed (as in nature) in salt water that occupies the interstitial space of the partially water-saturated silica sand bed. The experiments demonstrate that the rate of hydrate formation is a function of particle diameter, gas source, water salinity, and thermodynamic conditions. The initiation time of hydrate formation was very short and pressure decreased rapidly in the initial stage. The process of mixed gas hydrate formation can be divided into three stages for each type of sediment. Sand particle diameter and water salinity also can influence the formation process of hydrate. The conversion rate of water to hydrate was different under varying thermodynamic conditions, although the formation processes were similar. The conversion rate of methane hydrate in the 250-380 μm sediment was greater than that in the 150-250μm sediment. However, the sediment grain size has no significant influence on the conversion rate of mixed gas hydrate.展开更多
The P-T stability conditions of gas hydrate in different systems （i.e., solution, silica sand, and marine sediment） were studied using multi-step decomposition method with our experimental equipment. The effects of ...The P-T stability conditions of gas hydrate in different systems （i.e., solution, silica sand, and marine sediment） were studied using multi-step decomposition method with our experimental equipment. The effects of different ions with various concentra- tions and sediment grains on the P-T stability conditions of gas hydrate were investigated. The results show that different ions have different influences on the phase equilibrium of gas hydrate. However, the influence of ions is in a similar trend： the larg- er the concentration, the bigger the P-T curve shifts to the left. For the silica sand, the influence of pore capillarity of coarse particles （〉 460 ~tm） can be negligible. The P-T curve measured in coarse silica is in agreement with that in pure water. How- ever, the influence of pore capillarity of fine particles （〈 35 μm） is significant. The maximum reduction value of temperature is 1.5 K for methane hydrate under stable state. The sediment from the South China Sea significantly affects the P-T stability conditions of methane hydrate, with an average reduction value of 1.9 K within the experimental conditions. This is mainly the result of both the pore water salinity and the pore capillarity of sediment. Because the pore water salinity is keeping diluted by the fresh water released from hydrate dissociation, the measured P-T stability points fall on different P-T curves with the de- creasing salinity.展开更多
基金provided by the NSFC-Guangdong Joint Science Foundation of China (Grant No. U0933004)the National Basic Research Program of China (Grant No. 2009CB219504)+3 种基金the National Natural Science Foundation of China (Grant No. 51206169)the National Oceanic Geological Special Projects (Grant No. GHZ2012006003)the Knowledge Innovation Program of the Chinese Academy of Sciences (Grant No.KGZD-EW-3)the National High Technology Research and Development Program of China (Grant No. 2012AA061403-03)
文摘Gas hydrate formation from two types of dissolved gas (methane and mixed gas) was studied under varying thermodynamic conditions in a novel apparatus containing two different natural media from the South China Sea. The testing media consisted of silica sand particles with diameters of 150-250 μm and 250-380 μm. Hydrate was formed (as in nature) in salt water that occupies the interstitial space of the partially water-saturated silica sand bed. The experiments demonstrate that the rate of hydrate formation is a function of particle diameter, gas source, water salinity, and thermodynamic conditions. The initiation time of hydrate formation was very short and pressure decreased rapidly in the initial stage. The process of mixed gas hydrate formation can be divided into three stages for each type of sediment. Sand particle diameter and water salinity also can influence the formation process of hydrate. The conversion rate of water to hydrate was different under varying thermodynamic conditions, although the formation processes were similar. The conversion rate of methane hydrate in the 250-380 μm sediment was greater than that in the 150-250μm sediment. However, the sediment grain size has no significant influence on the conversion rate of mixed gas hydrate.
基金financially supported by the National Basic Research Program of China (Grant No. 2009CB219503)the National Natural Science Foundation of China (Grant No. 41072037)
文摘The P-T stability conditions of gas hydrate in different systems （i.e., solution, silica sand, and marine sediment） were studied using multi-step decomposition method with our experimental equipment. The effects of different ions with various concentra- tions and sediment grains on the P-T stability conditions of gas hydrate were investigated. The results show that different ions have different influences on the phase equilibrium of gas hydrate. However, the influence of ions is in a similar trend： the larg- er the concentration, the bigger the P-T curve shifts to the left. For the silica sand, the influence of pore capillarity of coarse particles （〉 460 ~tm） can be negligible. The P-T curve measured in coarse silica is in agreement with that in pure water. How- ever, the influence of pore capillarity of fine particles （〈 35 μm） is significant. The maximum reduction value of temperature is 1.5 K for methane hydrate under stable state. The sediment from the South China Sea significantly affects the P-T stability conditions of methane hydrate, with an average reduction value of 1.9 K within the experimental conditions. This is mainly the result of both the pore water salinity and the pore capillarity of sediment. Because the pore water salinity is keeping diluted by the fresh water released from hydrate dissociation, the measured P-T stability points fall on different P-T curves with the de- creasing salinity.
