深层页岩干酪根热成熟度对CH₄/CO₂气体吸附机理影响机制研究

Adsorption Mechanisms and Mathematical Models of CH₄/CO₂ in Kerogen with Thermal Maturity

摘要: 在全球能源转型背景下，页岩气高效开发与CO₂地质封存的协同优化需求迫切。干酪根作为页岩气吸附的核心载体，目前仍然缺乏不同干酪根热成熟度对CH₄/CO₂吸附行为影响的研究。通过分子动力学构建3类非均质干酪根纳米孔隙模型，结合蒙特卡洛方法模拟储层温压条件下气体的吸附行为，并对比吸附数学模型的拟合效果。结果显示：① CH₄/CO₂气体在干酪根上的吸附量呈现III-A型 > II-C型 > I-A型的规律，归因于Ⅲ型干酪根因孔隙结构复杂、范德华力强且极性基团丰富；② 温度升高会导致吸附量下降，符合放热吸附机制，而压力升高使吸附行为经历低压时指数增长、中压时缓慢增长和高压时趋于饱和；③ 模型对比表明，L-F模型因引入多层吸附及分子间作用修正项，拟合效果最佳。该研究揭示了干酪根热成熟度对气体吸附的调控机理，可为页岩气开采和CO₂封存技术的优化提供了理论支持。

Abstract: In the context of global energy transformation, there is an urgent need for collaborative optimization between efficient shale gas development and geological CO₂ sequestration. Kerogen, acting as the primary medium for shale gas adsorption, has seen limited research regarding how varying degrees of kerogen thermal maturity influence the adsorption behavior of CH₄/CO₂. By employing molecular dynamics simulations, three distinct heterogeneous kerogen nanopore models were developed. Using the Monte Carlo method, the gas adsorption behavior under reservoir temperature and pressure conditions was analyzed. Additionally, the fitting performance of various adsorption mathematical models was compared. The findings are summarized as follows: ① The adsorption capacity of CH₄/CO₂ on kerogen follows the order of Type III-A > Type II -C > Type I -A. This trend can be attributed to the intricate pore structure, strong van der Waals forces, and abundant polar groups characteristic of Type III kerogen; ② An increase in temperature results in reduced adsorption capacity, consistent with the exothermic nature of the adsorption process. Meanwhile, increasing pressure leads to exponential growth at low pressures, gradual growth at intermediate pressures, and saturation at high pressures; ③ Model comparisons reveal that the L-F model demonstrates superior fitting performance due to its incorporation of multi-layer adsorption and intermolecular interaction correction terms. This study elucidates the regulatory mechanism of kerogen thermal maturity on gas adsorption and offers theoretical guidance for enhancing shale gas extraction and CO₂ sequestration technologies.