Vol.5 No.2 2012

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研究論文:Development of methane hydrate production method(長尾)−94−Synthesiology Vol.5 No.2(2012)the temperature of the high-pressure vessel from −5 to 20 °C. Holes in the sides and bottom of the vessel for the insertion of gas and water are connected to a CH4 gas supplier and pumps that supply pure water into the sandy sample layers, respectively. The production well is connected to a gas and water separator. Real-time observations of the rate of the production of gas and water as well as the amount of fine sand particles can be performed under various temperature and pressure conditions.Pure water is injected into the high-pressure vessel via the holes in the sides of the vessel and the centre pipe. Once the designated amount of pure water has been filled in the vessel, sand particles are added to the pure water, and vibration is applied to ensure homogeneous accumulation of sand particles. After the vessel is filled with wet sand particles, the inner plate is positioned above the sand sample layer, and the top chamber is closed. Pure water is injected into the interior of the top chamber to apply overburden pressure to the sandy sample layer by pressurizing the inner plate. To adjust the water content, water in the sandy sample layer can pass through the holes in the bottom of the vessel.For the formation of methane hydrate in the sandy sample layer and control of the confinement pressure, the flow rate of CH4 is adjusted. CH4 is continuously supplied via holes in the sides of the vessel. The temperature of the cabinet is decreased below the equilibrium temperature of methane hydrate formation. By calculating the injected volume of methane gas and the initial water content, the end of the methane hydrate formation can be estimated. After methane hydrate formation, pure water is injected into the pore spaces of the sandy sample layer because natural gas hydrate reservoirs are usually saturated with water.The top of the centre pipe is connected to a backpressure regulator. To examine the depressurization method, the pressure value of the regulator is adjusted to a designated pressure. After adjustment, gas and water flow out through the centre pipe, which may contain fine sand components. The centre pipe is connected to the gas-water separator, and each line tube is connected to a fluid flow metre that measures water and gas volumes during the experiment. To evaluate the sand production phenomenon, a water flow line is connected to the accumulation chamber to collect the fine sand particles.Figure 6 shows the predictions of water and gas production by the MH21-HYDRES production simulator using the results of depressurization experiments conducted in the large-scale laboratory reactor. The results show the water and gas production behaviours when pressure is decreased from 10 to 3 MPa. The parameters for the numerical simulation were temperature of 10 °C, pressure of 10 MPa, permeability of sandy sample layer of 1000 mD[17], initial effective 1.4 mTubePorous spacer3.2 msandwaterwellPumpLow temperature roomgas, water inletHoleswall(Laser position meter)Gas and waterControl PCSampling padWater/sandSeparatorGasDe-pressuring tank(a) High-pressure vessel of the large-scale laboratory reactor(b) Schematic flow diagram of the large-scale laboratory reactorFig. 5 Schematic illustrations of the large-scale laboratory reactorTo aid the development of technologies for advanced production methods and to analyze the impact of sand production, skin formation and flow obstructions, the highly sensitive temperature and pressure sensors with a wide range and fluid flow metres are arrayed to side holes of the vessel. To evaluate the sand production phenomena, a sand screen is fitted to a well tube. Water and fine sand are collected in a sampling pod arrayed to the water/gas separator. The overall gas volume is measured at de-pressuring tank arrayed to the water/gas separator. All measured data were collected in a PC automatically.

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