甲烷在干酪根中的吸附及扩散特性

Characteristic of Adsorption and Diffusion for Methane in Kerogen

本文采用巨正则蒙特卡罗和分子动力学方法研究了甲烷在两种干酪根(kerogenⅡ-A和kerogenⅡ-D)中的吸附和扩散特性,分析了温度、压力、埋藏深度及混有二氧化碳时对甲烷吸附扩散的影响。结果表明:甲烷吸附量随着地层温度的增加而减小,随着地层压力的增加而增大,且压力对吸附量的影响比温度大,随着埋存深度的增加先增大后减小,在3~4 km时达到最大值;同时甲烷的扩散系数也随着埋存深度的增加先增大后减小;当甲烷中混有二氧化碳时,甲烷的吸附量明显小于单组分甲烷的吸附量,表明二氧化碳将抑制甲烷的吸附,也将促进甲烷的扩散,这说明注二氧化碳技术对于页岩气的开发有利。研究结果将在分子层面为页岩气的宏观勘探开采提供理论指导。

In this paper, the adsorption and diffusion characteristics of methane were studied by the Monte Carlo method and the molecular dynamics method in two types of kerogen, including kerogenⅡ-A and kerogen Ⅱ-D. The effects of temperature, pressure, depth of burial and carbon dioxide on methane adsorption and diffusion were investigated. The results show that the adsorption amount of methane decreases with the increase of temperature. Conversely, it increases with the increase of pressure. The influence of pressure on adsorption amount is greater than that of temperature.With the increase of burial depths, the adsorption amount of methane increase firstly. At the 3~4 km geological depths, the figure reaches the highest point. Then, the figure experienced a downward trend. At the same time, the diffusion coefficient also shows the same trend as the increase of burial depth. When the carbon dioxide is mixed with methane, the adsorption amount of methane is obviously smaller than that of single component methane, indicating that carbon dioxide will suppress methane adsorption and will also promote the diffusion of methane. This shows that injection carbon dioxide can displace methane to achieve efficient development of shale gas. The results will provide theoretical guidance for macro-exploration and exploitation of shale gas at the molecular level.