Molecular simulation of the displacement of shale gas in quartz slit by flue gas
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摘要: 为了探究石英狭缝孔中烟道气封存联合页岩气采收技术的效率,采用巨正则蒙特卡洛(GCMC)和分子动力学(MD)模拟探讨了地质埋深、地层水含量和烟道气注入比例对烟道气(CO2/N2)驱替石英狭缝孔中页岩气(CH4)效率的影响。通过系统分析各组分的密度分布、负载量、吸附热和相互作用能,确定了各组分的吸附机理和CH4的采收率。混合组分中CH4和N2的负载量(ΓCH4和ΓN2)与地层水含量呈负相关。随着地质埋深的增大,ΓCH4和ΓN2迅速增大,在埋深达到2 400 m后趋于平缓。CO2的负载量(ΓCO2)在埋深2 400 m出现最大值;在埋深小于2 400 m时,ΓCO2与地层水含量呈正相关;埋深大于2 400 m后,ΓCO2与地层水含量呈负相关。CH4的采收率在埋深400~600 m处出现最大值,并随烟道气中CO2摩尔分数的增大而增大,表明烟道气中的CO2对CH4有较强的驱替能力。Abstract: To study the efficiency of flue gas sequestration with enhanced shale gas recovery in quartz slit, Grand Canonical Monte Carlo (GCMC) and Molecular Dynamics (MD) simulations were adopted to investigate the influence of burial depth, formation water content and the injection ratio of flue gas on the recovery efficiency of shale gas (CH4) in quartz slit by flue gas (CO2/N2). The density distribution, loading, adsorption heat and interaction energy of each component were systematically analyzed to reveal their adsorption mechanisms and the recovery efficiency of CH4. It indicates that the loadings of mixed CH4 and N2 (ΓCH4 and ΓN2) exhibit negative correlation with formation water content. With the increasing burial depth, both ΓCH4 and ΓN2 increase at first and then tend to be constant when the burial depth is over 2 400 m. The maximum loading of CO2 (ΓCO2) occurs at the burial depth of 2 400 m. There is a positive correlation of ΓCO2 with formation water content when the burial depth is below 2 400 m, and a negative correlation when the burial depth is over 2 400 m. The recovery efficiency of CH4 (η) reaches the maximum point at the burial depth of 400-600 m, which increases with the increasing mole fraction of CO2 in flue gas, showing that CO2 in flue gas can promote the displacement of CH4 significantly.
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Key words:
- shale gas /
- flue gas /
- competitive adsorption /
- recovery efficiency /
- quartz /
- molecular simulation
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表 1 渤海湾盆地东北海区不同地质埋深(Bd)对应的温度(T)和压力(P)[21]
Table 1. Temperatures and pressures at different burial depths in the northeast sea area of Bohai Bay Basin
Bd/m T/K P/MPa Bd/m T/K P/MPa Bd/m T/K P/MPa 200 297.75 2.00 2 200 349.75 22.00 4 200 393.99 42.00 400 306.55 4.00 2 400 352.95 24.00 4 400 398.15 44.00 600 314.55 6.00 2 600 357.83 26.00 4 600 402.23 46.00 800 321.75 8.00 2 800 362.63 28.00 4 800 406.23 48.00 1 000 328.15 10.00 3 000 367.35 30.00 5 000 410.15 50.00 1 200 333.75 12.00 3 200 371.99 32.00 5 200 415.03 52.00 1 400 338.55 14.00 3 400 376.55 34.00 5 400 419.37 54.00 1 600 342.55 16.00 3 600 381.03 36.00 5 600 424.23 56.00 1 800 345.75 18.00 3 800 385.43 38.00 5 800 428.51 58.00 2 000 348.15 20.00 4 000 389.75 40.00 6 000 433.35 60.00 -
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