Molecular dynamics simulations of CH4 diffusion in kaolinite: influence of water content

Abstract

Understanding the interaction of CH 4 with kaolinite is significant for researchers in the fields of coalbed CH 4 and shale gas. The diffusion behaviors of CH 4 in kaolinite with water contents ranging from 0 to 5 wt% have been analyzed by molecular dynamics simulations. The results of the simulations indicate that CH 4 molecules can jump between adjacent holes in the kaolinite matrix. CH 4 diffusion coefficient was very low (3.28 9 10 -9 m 2 /s) and increased linearly with the increasing of water content. As the water content decreased, the value of radial distribution function first peak between CH 4 and oxygen was larger, meaning that with lower water content, the interaction energy between CH 4 and oxygen in kaolinite is stronger. The interaction between CH 4 and water is linearly positively correlated with water content, in contrast, the interaction energy between kaolinite and water as well as between kaolinite and CH 4 decreased linearly with increasing water content. On the other hand, the diffusion of CH 4 molecules adsorbed on the surfaces also can be accelerated by the fast diffusion of water molecules in the middle micropore of the kaolinite.

Influence of H2O on Adsorbed CH4 on Coal Displaced by CO2 Injection: Implication for CO2 Sequestration in Coal Seam with Enhanced CH4 Recovery (CO2-ECBM)

“…The η of moisture-equilibrated coals at each CO 2 injection pressure is greater than that of dry coals, indicating that H 2 O could increase the CH 4 desorption ratio. However, the increasing CH 4 desorption ratio does not indicate the enhanced CH 4 desorption amount ( n des,CH 4 ) due to the fact that H 2 O can decrease n abs,CH 4 ,initial Figure displays the n des,CH 4 at displacement equilibrium.…”

“…However, the increasing CH 4 desorption ratio does not indicate the enhanced CH 4 desorption amount (n des,CH 4 ) due to the fact that H 2 O can decrease n abs,CH 4 ,initial . 100 Figure 17 displays the n des,CH 4 at displacement equilibrium. The n des,CH 4 of moisture-equilibrated coals follows the order of SH > DQ > SCG, which agrees with the sequence of η.…”

Electrochemical Modification on CH4 and H2O Wettability of Qinshui Anthracite Coal: A Combined Experimental and Molecular Dynamics Simulation Study

“…The CH 4 self-diffusion coefficient was gained by calculating the mean square displacement over time, as shown in Figure . The transport diffusion coefficient was also obtained by the Maxwell–Stefan diffusion model .…”

“…With the continuous increase in adsorption pressure, the mechanical compression induced by pressure continues to increase, while the increase in adsorbed CH 4 is limited. 31 As a result, the volume of anthracite decreases. After electrochemical modification, the adsorption capacity of anthracite to methane decreased, resulting in the volume change of anthracite sample after modification being smaller than that before modification in the initial stage.…”

Influence of Long Boreholes Layout and Drilling Length on Gas Drainage Based on Multifield Coupling Model of Gas‐Bearing Coal

“…If the length of the borehole is too large, due to the attenuation of the negative pressure in the borehole, the gas content at the bottom of the long borehole will be high, making it difficult to reach the drainage index. If the length of the borehole is too short, it will result in low efficiency of gas drainage measures [23][24][25]. At present, the methods to determine the effective gas drainage radius include on-site measurement and theoretical calculation methods [26,27].…”