The natural occurrence of methane hydrates in marine sediments has been intensively studied over the past decades, and geochemical charac-teristic of hydrate is one of the most attractive research fields. In this pape...The natural occurrence of methane hydrates in marine sediments has been intensively studied over the past decades, and geochemical charac-teristic of hydrate is one of the most attractive research fields. In this paper, we discussed the geochemical anomaly during hydrate formation in porous media. By doing so, we also investigated the temperature influence on hydrate formation under isobaric condition. It turns out that sub-cooling is an important factor to dominate hydrate formation. Larger subcooling provides more powerful driving force for hydrate formation. During the geochemical anomaly research, six kinds of ions and the total dissolved salt （TDS） were measured before and after the experiment in different porous media. The result is that all kinds of ionic concentration increased after hydrate formation which can be defined as salting out effect mainly affected by gas consumption. But the variation ratio of different ions is not equal. Ca^2＋ seems to be the most significantly influenced one, and its variation ratio is up to 80%. Finally, we theoretically made a model to calculate the TDS variation, the result is in good accordance with measured one, especially when gas consumption is large.展开更多
Sediment-hosted hydrate reservoir often contains saturated pore fluid, which changes the heat transfer and mass transfer characteristics of the hydrate reservoir. The exploitation of hydrate under saturated pore fluid...Sediment-hosted hydrate reservoir often contains saturated pore fluid, which changes the heat transfer and mass transfer characteristics of the hydrate reservoir. The exploitation of hydrate under saturated pore fluid using depressurization is simulated experimentally to investigate the influence of particle size of porous media, dissociation temperature, pressure drop and injected fluid type on gas production behavior. Homogeneous methane hydrate was firstly formed in frozen quartz sand. With the formed hydrate sample, hydrate dissociation experiments by depressurization were conducted. The test results showed that the gas production rate of hydrate under saturated pore fluid was substantially influenced by the particle size, the pressure drop and the injected fluid type, while it was influenced little by the dissociation temperature. The hydrate dissociates faster under larger pressure drop and in the presence of smaller porous media within the experimental region. The dissociation rate increases with an increasing fluid salinity in the initial stage, while it decreases in the later stage. The increase of gas diffusion resistance resulted from ionic hydration atmosphere in saturated chloride solution impeded the dissociation of hydrate. It can be solved by increasing the pressure drop and decreasing the fluid salinity in the process of gas recovery from hydrate reservoir.展开更多
基金Supported by Natural Gas Hydrate in China Sea Exploration and Evaluation Project (G2H200200202)National Basic ResearchProgram of China (973 Program, Grant No. 2009CB219503)
文摘The natural occurrence of methane hydrates in marine sediments has been intensively studied over the past decades, and geochemical charac-teristic of hydrate is one of the most attractive research fields. In this paper, we discussed the geochemical anomaly during hydrate formation in porous media. By doing so, we also investigated the temperature influence on hydrate formation under isobaric condition. It turns out that sub-cooling is an important factor to dominate hydrate formation. Larger subcooling provides more powerful driving force for hydrate formation. During the geochemical anomaly research, six kinds of ions and the total dissolved salt （TDS） were measured before and after the experiment in different porous media. The result is that all kinds of ionic concentration increased after hydrate formation which can be defined as salting out effect mainly affected by gas consumption. But the variation ratio of different ions is not equal. Ca^2＋ seems to be the most significantly influenced one, and its variation ratio is up to 80%. Finally, we theoretically made a model to calculate the TDS variation, the result is in good accordance with measured one, especially when gas consumption is large.
基金supported by the National Natural Science Foundation of China(Grant No.51304079,Grant No.51474112,Grant No.41502343 and Grant No.51506073)
文摘Sediment-hosted hydrate reservoir often contains saturated pore fluid, which changes the heat transfer and mass transfer characteristics of the hydrate reservoir. The exploitation of hydrate under saturated pore fluid using depressurization is simulated experimentally to investigate the influence of particle size of porous media, dissociation temperature, pressure drop and injected fluid type on gas production behavior. Homogeneous methane hydrate was firstly formed in frozen quartz sand. With the formed hydrate sample, hydrate dissociation experiments by depressurization were conducted. The test results showed that the gas production rate of hydrate under saturated pore fluid was substantially influenced by the particle size, the pressure drop and the injected fluid type, while it was influenced little by the dissociation temperature. The hydrate dissociates faster under larger pressure drop and in the presence of smaller porous media within the experimental region. The dissociation rate increases with an increasing fluid salinity in the initial stage, while it decreases in the later stage. The increase of gas diffusion resistance resulted from ionic hydration atmosphere in saturated chloride solution impeded the dissociation of hydrate. It can be solved by increasing the pressure drop and decreasing the fluid salinity in the process of gas recovery from hydrate reservoir.
