北京大学关平研究团队报道了了无机矿物纳米孔中氦传输的分子动力学模拟。2024年11月25日，《中国科学：地球科学》发表了这一成果。

氦在纳米尺度无机矿物孔隙和孔喉中的运移是其整体运移的关键。为了阐明氦在纳米孔内的输运动力学，研究小组采用平衡和非平衡分子动力学模拟，研究了氦在石英狭缝状纳米孔中的静态自扩散和压力驱动流动。研究人员还将水和各种气体（包括氢、甲烷、乙烷、氮和二氧化碳）引入纳米孔，以评估它们对氦传输的影响。

他们的发现表明石英孔表面的氦吸附极小。孔径小于5nm和压强在10以下MPa、环境因素对氦的扩散有显著影响。大孔径、高温和低压增强了氦的解吸，促进了更快的扩散。研究人员观察到氦气流速与孔隙大小、压力梯度和表面光滑度等因素呈正相关。

值得注意的是，石英纳米孔中存在孔隙水和载气，其扩散速度比氦慢，倾向于减少氦的表面吸附，减缓其扩散。在所研究的载气中，氮气的吸附容量、扩散率和稳定性与氦气相似，而二氧化碳的吸附容量最高，扩散率最慢，与氦气有明显差异。

根据模拟结果，研究人员得出，水和载气在氦迁移过程中主要作为输运介质，与氦一起移动。氮与氦具有相似的性质，有效地协助了这一共迁移过程。相反，二氧化碳由于其高吸附能力和缓慢扩散，在共迁移过程中容易丢失。因此，具有高氮含量和低二氧化碳含量的气藏更有可能具有较高的氦浓度。盖层中较小的孔隙尺寸和较高的气体压力会阻碍氦的扩散，有利于其在储层中的保存。此外，水的存在和载体气体显著阻碍这些毛孔，阻碍氦的逃逸。

附：英文原文

Title: Molecular dynamics simulations of helium transport through inorganic mineral nanopores

Author: Dandan SONG, Ping GUAN, Chi ZHANG, Jiahao REN

Issue&Volume: 2024/11/25

Abstract: Helium transport through nanoscale inorganic mineral pores and pore throats is essential for its overall migration. To elucidate helium’s transport dynamics within nanopores, we employed equilibrium and non-equilibrium molecular dynamics simulations to investigate helium’s static self-diffusion and pressure-driven flow in quartz slit-shaped nanopores. We also introduced water and various gases, including hydrogen, methane, ethane, nitrogen, and carbon dioxide, into the nanopores to assess their influence on helium transport. Our findings indicate minimal helium adsorption on quartz pore surfaces. Under conditions where the pore size is less than 5nm and the pressure under 10MPa, environmental factors markedly influence helium diffusion. Large pore sizes, high temperatures, and low gas pressures enhance helium desorption and facilitate faster diffusion. We observed a positive correlation between helium flow velocity and factors such as pore size, pressure gradient, and surface smoothness of the pores. Notably, the presence of pore water and carrier gases in quartz nanopores, which diffuse more slowly than helium, tends to reduce helium surface adsorption and slow its diffusion. Among the carrier gases studied, nitrogen showed similar adsorption capacity, diffusivity, and stability to helium, while carbon dioxide displayed the highest adsorption capacity and the slowest diffusion rate, markedly differing from helium. Based on the simulation results, we concluded that water and carrier gases primarily function as transport mediums in helium migration, moving together with helium. Nitrogen, which shares similar properties with helium, effectively assists in this co-migration process. Conversely, carbon dioxide, due to its high adsorption capacity and slow diffusion, tends to be lost during co-migration. As a result, gas reservoirs with high nitrogen levels and low carbon dioxide levels are more likely to have higher helium concentrations. Additionally, the smaller pore sizes and higher gas pressures in caprocks can impede helium’s diffusion, favoring its preservation in reservoirs. Moreover, the presence of water and carrier gases significantly obstructs these pores, further hindering helium’s escape.

DOI: 10.1007/s11430-024-1441-y

Source: https://www.sciengine.com/SCES/doi/10.1007/s11430-024-1441-y