Experimental Research And Process Simulation Of Natural Gas Hydrate Replacement Production By Injecting CO₂+N₂ Mixture Gas

Natural gas could be produced by CO₂ replacement method from natural gas hydrate reservoirs and CO₂ is sequestered simultaneously.The formation of CO₂ hydrate plays an important role in stabilizing reservoir,which could avoid slope failure and seabed ecosystem destruction during replacement process.However,the replacement method is restricted by the source of CO₂.Although flue gas from power plant is employed to reduce purification cost of CO₂,the concentration of CO₂ is less than 20% which confined the production of natural gas.To overcome this problem,a natural gas hydrate production method is proposed by injecting rich CO₂ gas?CO₂ + N₂ mixture gas?obtained by flue gas hydrate separation in this workIn this paper,ice powder and methane in the quartz sand system was used to simulate hydrate reservoir.The experiment was conducted to simulate the replacement process of the methane production from methane hydrate by injecting CO₂ at the temperature of 1⁸? and the pressure of 2.1³.4 MPa and by injecting 53%CO₂ + 47%N₂ mixture gas at the temperature of 1¹4? and the pressure of 6.5¹4 MPa.The replacement processes were compared respectively by injecting CO₂,53%CO₂ + 47%N₂ mixture gas and flue gas with CO₂ partial pressure of 3.4 MPa and replacement temperature of 1?.The mechanism of decomposition-diffusion was proposed that CH₄ was produced by injecting CO₂ + N₂ mixture gas from hydrate reservoir.At the end of this paper,energy efficiency of two schemes,flue gas-replacement production-membrane separation and flue gas-hydrate separation-replacement production-membrane separation,were used to simulate and be compared by Aspen software.The experimental results of replacement process showed that the recovery ratio and the concentration of methane in the gas phase increased with replacement temperature rising,no matter what CO₂ or 53%CO₂ + 47%N₂ was injected.The best performance of CO₂ replacement was 46.6% of CH₄ recovery ration and 0.13 of CH₄ concentration after about 142 h at 8?.For 53%CO₂ + 47%N₂ mixture gas replacement process,the best performance was conducted at 14? in the range of experimental temperature.97.0% of CH₄ recovery ratio and0.15 of CH₄ concentration were obtained after about 66 h.The concentration of methane in the gas phase reduced significantly with pressure increasing by injecting CO₂ or 53%CO₂ +47%N₂ mixture gas within the examined pressure range.During the process of CO₂ replacement,the CH₄ recovery ration was rising with pressure increase.While the CH₄ recovery ration was decreasing with pressure increase during the process of 53%CO₂ +47%N₂ mixture gas replacement.When the injection pressure of CO₂ increased from 2.1 MPa to 3.4 MPa,the CH₄ recovery ration rose from 12.6% to 19.0% and the CH₄ concentration in the gas phase decreased from 0.14 to 0.06.When the injection pressure of 53%CO₂ + 47%N₂mixture gas increased from 6.5 MPa to 13.8 MPa,the CH₄ recovery ration drop from 17.0%to 6.3% and the CH₄ concentration in the gas phase decreased from 0.07 to 0.01.The ranking performance of replacement with CO₂ partial pressure of 3.4 MPa at 1? was: injecting CO₂ >injecting 53%CO₂ + 47%N₂ > injecting 19%CO₂ + 81%N₂.Aspen simulation results showed that the energy efficiency of scheme two was higher than the energy efficiency of scheme one when the injection pressure was 3¹0 MPa.The energy efficiency of scheme two and scheme one was almost equal when the injection pressure was 10¹6 MPa.