Study On Thermal Effect Of Hydrate Formation And Decomposition Process In Water-rich Quartz Sand System

Natural gas hydrate is a kind of crystalline substance similar to ice.It has a high energy density and is widely distributed in the bottom of the ocean and in the plateau tundra.It is considered to be an important clean energy source in the 21st century and is valued by all countries in the world.The research goal of natural gas hydrate mining technology is to improve efficiency,reduce risks and reduce costs.The premise of exploration and mining is to master the reservoir formation mechanism of natural gas hydrates.In this thesis,the differential scanning calorimeter was used to investigate the thermal changes of the hydrate formation and decomposition process,and a small threedimensional equipment was built to carry out the hydrate decomposition simulation experiment under the conditions of heat injection and depressurization,and the temperature,pressure and gas volume production in the process were explored.The main contents of this thesis are as follows:(1)The heat change during the phase change of hydrate was obtained by using differential scanning calorimeter(DSC)with temperature programmed method.The effects of quartz sand particle size,initial moisture content,temperature and salt content on the exothermic change during the formation and decomposition of methane hydrate were investigated.The experimental results show that the heat release increases with the increase of sediment number in the process of hydrate phase change.The heat release first increases and then decreases with the increase of water content,and the heat release accumulation is the largest under the condition of 50% water content.The heat transfer law of saltcontaining system is similar to that of pure water system,and the reaction rate and conversion rate are lower than those in the pure water system.(2)The small three-dimensional reactor was used to simulate the marine water-rich environment,and the changes of temperature,pressure and gas production during the formation and decomposition of hydrate under heat injection and depressurization were investigated.The experimental results show that after the gas is introduced into the kettle,the hydrate is formed in a large amount,the temperature in the kettle rises rapidly,and the pressure decreases.During the decomposition process,the hydrates in the system decompose almost at the same time,the temperature rapidly decreases,and the gas production rate decreases with the decomposition.The rate of decomposition of hydrate increases after hot water injection.As the temperature of the injected hot water increases,the decomposition rate of the hydrate increases continuously.In general,the heat injection process is inefficient and the heat transfer loss in the reactor is large.