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模拟煤储层中甲烷(CH4)在不同孔径中不同水分下的解吸和扩散过程,讨论孔径、含水率、温度和压力与CH4解吸扩散的关系。结果表明,狭缝的壁面叠加效应会显著影响H2O分子的吸附/解吸,使H2O分子集中分布在狭缝孔的中间位置。当孔间距逐渐增大时,双侧壁面叠加效应逐渐转化为单侧壁面的表面效应对H2O分子的吸附,使H2O分子的分布由中间转为两边。含水率的增加对CH4解吸的影响程度增加,CH4的解吸量呈减小趋势,但受温度影响规律不明显。在1nm狭缝孔中,低压时的水分对CH4解吸的影响程度大于高压下的情况。在2nm狭缝孔中,当含水率由2.35%增加至5%时,低压时的水分对CH4解吸的影响程度则开始小于高压下的情况。在5nm狭缝孔中,随着压力的降低,含水率对CH4解吸量的影响变得不明显,说明在解吸过程中,压力降到某一值后,改变含水率并不会促进CH4的解吸;当含水率超过2.35%时,含水率的增加仍然对CH4的解吸产生影响,说明2.35%并不是石墨狭缝孔的水分临界值,但由于随着含水率的增加,CH4所受的影响程度逐渐变小,因此临界值可能存在。微孔中水的吸附热和微孔对吸附质分子的强吸附势使孔径和含水率显著影响CH4的扩散系数,而温度和压力对CH4的扩散系数则影响较小。
Simulate the desorption and diffusion process of methane (CH4) in different pore sizes in coal reservoirs, and discuss the relationship between pore size, water content, temperature and pressure and the desorption and diffusion of CH4. The results show that the superposition of the walls of the slits can significantly affect the adsorption / desorption of H2O molecules, so that the H2O molecules are concentrated in the middle of the slit pores. When pore spacing increases, the superposition effect of double-wall gradually transforms into the adsorption of H2O on the surface effect of single-wall, which makes the distribution of H2O molecules turn from the middle to the two sides. The effect of increasing moisture content on the desorption of CH4 increased, while the desorption amount of CH4 decreased. However, the influence of temperature was not obvious. In the 1nm slit, the effect of moisture at low pressure on desorption of CH4 is greater than that at high pressure. In the 2nm slit, when moisture content increased from 2.35% to 5%, the effect of moisture at low pressure on CH4 desorption began to be less than that at high pressure. In the 5nm slit, with the decrease of pressure, the influence of water content on CH4 desorption amount becomes insignificant, which shows that in the process of desorption, after the pressure drops to a certain value, changing the water content does not promote the desorption of CH4 ; When the moisture content exceeds 2.35%, the increase of water content still affects the desorption of CH4, indicating that 2.35% is not the critical value of moisture in graphite slit pores. However, as the moisture content increases, the degree of influence of CH4 Gradually smaller, so the threshold may exist. Adsorption heat of micropore water and strong adsorption of micropores on adsorbate molecules make pore size and water content significantly affect the diffusion coefficient of CH4, while temperature and pressure have less effect on the diffusion coefficient of CH4.