构造煤的超临界吸附/解吸特性及其机理

Supercritical adsorption/desorption is the key issue during the coalbed methane exploitation in the deep tectonically deformed coal developed areas. This project focuses on the key scientific issue of the coupling relationship between supercritical adsorption/desorption and the structure of tectonically deformed coal. A series of tectonically deformed coals with distinct deformation mechanisms and deformation degrees, and the corresponding undeformed coal will be chosen as the research objects. Firstly, supercritical isothermal adsorption/desorption tests of CO2, CH4 and their mixed gas will be carried out. Through analyses of supercritical adsorption/desorption behaviors and thermokinetic characteristics, basic change laws of adsorption/desorption properties of tectonically deformed coal will be discussed, and the supercritical adsorption model of the tectonically developed coal will be established or modified. Secondly, we will present coupling analyses of the relationships between the pore structure, chemical composition/structure and its supercritical adsorption/desorption behaviors and thermokinetic characteristics of the tectonically deformed coal, respectively. Evolutions of the relationships with the coal deformation degree will be analyzed. The control mechanism of structural deformation on the supercritical adsorption/desorption of the coal will be explored. Moreover, based on changes of physical and chemical structures and the supercritical adsorption/desorption of the undeformed coal before and after deformation tests at high temperature and pressure. Research results will provide the important theory basis for the potential evaluation of CO2 sequestration and improvement of CH4 recovery in the deep tectonically deformed coal developed areas.

超临界吸附/解吸是深部构造煤发育区煤层气资源开采中的核心问题。本项目围绕“构造煤超临界吸附/解吸与其结构的耦合关系”这一关键科学问题，以不同变形机制和变形程度的系列构造煤和相应的原生结构煤为研究对象，开展CO2、CH4及其混合气体的超临界等温吸附/解吸实验，通过分析构造煤超临界吸附/解吸行为和热动力学特征，探讨构造煤吸附/解吸特性的基本变化规律，建立或修正构造煤超临界吸附模型；耦合分析构造煤孔隙结构、化学组成/结构与其超临界吸附/解吸行为和热动力学特征之间的关系，并分析其随煤变形程度的演化规律，阐明构造变形对煤超临界吸附/解吸特性的控制机理；结合原生结构煤高温高压变形实验前后煤物理-化学结构变化和超临界吸附/解吸响应分析，建立构造煤超临界吸附/解吸特性与其变形机制之间的关系。研究结果可为深部构造煤发育区CO2封存潜力评估和促进煤层CH4采收率的提高提供重要的理论依据。

超临界吸附/解吸是深部煤层气资源开采的核心问题,也是深部煤层CO2封存潜力评估的关键。本项目通过构造煤样品宏、微观结构观测，研究了不同类型构造煤的宏-微观变形特征，划分出构造煤类型和变形机制。通过构造煤的CO2/CH4等温吸附解吸实验，基本阐明了构造煤的超临界吸附/解吸行为，认为构造煤超临界CO2吸附/解吸曲线以突变压力为界呈两段式变化，在吸附/解吸过程中均存在负吸附现象；超临界CH4过剩吸附/解吸曲线随压力的增加先升后降，存在吸附最大值，而其绝对吸附/解吸曲线先快速上升后逐渐变缓；随着变形程度的增加，构造煤超临界最大吸附量具增大趋势，而其吸附/解吸可逆性变化较复杂。构建了构造煤超临界吸附热动力学模型，认为格子模型能较好地预测超临界CH4的吸附行为，而超临界CO2吸附由于负吸附现象的存在，多项式方程呈现较好拟合优度。通过压汞实验、低温液氮/CO2吸附实验，揭示了构造煤孔隙结构演化对其超临界吸附/解吸特性的控制效应，认为极微孔是控制构造煤超临界CO2吸附的主要因素，而超临界CH4吸附受微孔影响明显，吸附/解吸可逆性主要受极微孔控制。通过XRD和FTIR实验，揭示了构造煤化学结构演化对其超临界吸附/解吸特性的控制效应，认为官能团为控制构造煤超临界吸附量的关键化学因素，构造煤化学结构演化对超临界CO2、CH4吸附/解吸可逆性控制作用相异。通过分析孔隙结构演化规律、煤基本结构单元演化模式、化学组成/结构的构造应力演化机制，分析了构造煤超临界吸附/解吸特性与其变形机制之间的关系。研究结果可为煤吸附气体本质或机理的揭示，及深部构造煤发育区CO2封存潜力评估和促进煤层CH4资源开采提供重要的理论依据。