页岩变形干酪根中甲烷吸附-解吸特征分子模拟

Molecular simulation of methane adsorption/desorption characteristics of deformed kerogen in shales

黄亮 徐侦耀 陈秋桔 田宝华 杨琴 冯鑫霓 曲自硕 杨哲 安思润

Liang HUANG Zhenyao XU Qiujie CHEN Baohua TIAN Qin YANG Xinni FENG Zishuo QU Zhe YANG Sirun AN

目前干酪根中甲烷吸附-解吸行为研究主要基于固定孔隙结构开展，干酪根孔隙变形对甲烷吸附-解吸的影响规律和作用机制尚不十分清楚。采用分子模拟方法研究了页岩干酪根中甲烷吸附-解吸行为及耦合的孔隙变形特征。构建和表征了干酪根纳米孔隙模型，研究了压力对干酪根变形的影响规律；用蒙特卡洛和分子动力学耦合方法，分析了甲烷吸附与干酪根变形的耦合特征；基于高压下吸附平衡的干酪根模型，进行了甲烷解吸模拟，研究了甲烷解吸滞后特征及解吸滞后成因。研究结果表明：①ⅡD型干酪根中极微孔为运移主通道，孤立的超微孔受孔隙变形影响具有运移潜力。②干酪根孔隙结构在压力上升和下降循环中基本上有可逆变化规律。③干酪根吸附变形过程分为体积膨胀和孔隙重组2个阶段。④结构变形可提高甲烷吸附能力，甲烷选择性吸附于干酪根中非均质的强亲和性位点，导致干酪根孔隙空间发生明显改变。⑤干酪根变形结构中观察到较小的解吸滞后环，孔隙变形是解吸滞后的重要诱因，吸附-解吸热力学差异与毛管凝聚效应不是甲烷解吸滞后现象产生的原因。

Current studies on the methane adsorption/desorption behavior in kerogen are primarily conducted based on fixed pore structures. Consequently， the influence patterns and mechanisms of the pore deformation of kerogen on methane adsorption/desorption remain poorly understood. Using molecular simulation， we explore both the methane adsorption/desorption behavior in shale kerogen and the coupled pore deformation characteristics. By constructing and characterizing a nanopore model of kerogen， we investigate the influence of pressure on kerogen deformation. Using a coupling method combining Grand Canonical Monte Carlo （GCMC） and molecular dynamics （also referred to as the GCMC-MD method）， we analyze the coupling characteristics of methane adsorption and kerogen deformation. Additionally， through methane desorption simulation using a kerogen model under high-pressure adsorption equilibrium， we investigate the characteristics and causes of methane desorption hysteresis. The results indicate that ultramicropores in Type ⅡD kerogen serve as the primary migration pathways， while isolated ultramicropores also have the potential to act as migration pathways due to the influence of pore deformation. The pore structures of kerogen generally are reversible during the pressure increase and decrease cycles. The methane adsorption-induced kerogen deformation can be divided into two stages： volume expansion and pore reorganization. The structural deformation of kerogen enhances the methane adsorption capacity， while the selective adsorption of methane onto high-affinity heterogeneous sites in kerogen leads to pronounced changes in pore space. Small desorption hysteresis loops are observed within the deformed structures of kerogen. The methane desorption hysteresis is primarily caused by pore deformation rather than the thermodynamic differences between adsorption and desorption and the capillary condensation effect.

10.11743/ogg20250320