页岩纳米孔隙中气体吸附微观机理研究

At present, research on the microcosmic mechanisms of shale nanometer pore concerning to the adsorption of gas is not much. The past studies mainly focused on that aspect related to single component, such as a certain mineral and organic matter in the shale. There is no effective measures formed to do the research on the microcosmic mechanisms of shale gas adsorption, which severely prevented the relative studies of shale gas, such as occurrence mechanism. Therefore, this project, based on the micro organic analysis of reservoirs and macro adsorption experiments, make use of the modified Tietz model to describe the interactive potential energy between moleculars in the shale gas, and between shale gas and pore wall. At the same time, this research makes use of molecular simulation to study the microcosmic mechanisms of the single component gas (CO2/CH4）、H2O) under the conditions of single component minerals (quartz, montmorillonite, kaolinite and illite etc.), organic matters (kerogen or activated carbon), and the mixtures of Multi-component minerals and organic matters and analyze microscopic mechanism of competitive adsorption of gas mixture（CO2 / CH4） with and without bound water conditions. It aims to quantize the relations between the adsorption quantity of shale gas and the parameters such as the interactive energies of molecular, heat of adsorption, density of adsorption phase and position of adsorption. Thus it intends to reveal the microcosmic mechanisms of shale gas and main influential factors, and hopefully, propose a reasonable theory foundation for the exploration of occurrence mechanism and development of shale gas.

目前国内外针对页岩纳米孔隙对气体吸附微观机理方面的研究较少，研究主要集中在对页岩某一种矿物及有机质等单组份吸附剂纳米孔隙中气体分子吸附微观机理方面，还未形成针对页岩气吸附微观机理研究的有效方法，严重制约了页岩气赋存机理等相关研究。因此，本项目在储层微观结构分析和宏观吸附实验的基础上，采用修正Tietz势能模型描述页岩气分子之间以及页岩气与孔壁之间的相互作用势能，利用分子模拟方法研究单组份气体（CO2/CH4）、H2O在单组份矿物（石英、蒙脱石、高岭石和伊利石等）、有机质（干酪根或活性炭）以及多组分混合矿物与有机质中的微观吸附机理，分析CO2/CH4混合气体在有无束缚水条件下的竞争吸附微观机理，量化不同温压、孔径条件下页岩气吸附量与分子间作用能、吸附热、吸附相密度、吸附位等参数之间关系，从而揭示页岩气吸附微观机理及主要影响因素，为探索页岩气的赋存机理和开采页岩气奠定基础。

目前国内外针对页岩纳米孔隙对气体吸附微观机理方面的研究较少，研究主要集中在对页岩某一种矿物及有机质等单组份吸附剂纳米孔隙中气体分子吸附微观机理方面，还未形成针对页岩气吸附微观机理研究的有效方法，严重制约了页岩气赋存机理等相关研究。因此，本项目采用场发射扫描电镜等分析储层微观结构，建立无机矿物（石英）、粘土矿物（蒙脱石、高岭石、伊利石）及有机质等纳米孔隙骨架模型，为准确的分子模拟计算提供基础。首次测试了已知三种矿物含量的混合矿物的吸附量，并以此为基础建立了新的适用于三组分混合黏土矿物的等温吸附预测模型及图版，只要已知页岩矿物组成便可根据该图版查取对应条件下的甲烷吸附量。基于建立的单组分矿物分子孔隙模型，利用蒙特卡洛模拟方法（MC）研究在地层温度压力下单组分气体（CO2/CH4）、H2O在单组分矿物（石英、蒙脱石、高岭石和伊利石等）和有机质（干酪根）的等温吸附量，分析吸附剂与吸附质之间相互作用势能和静电能、吸附热及吸附相密度等特性参数变化，量化不同温压、孔径条件下页岩气吸附量与分子间作用能、吸附热、吸附相密度、吸附位等参数之间关系，从而揭示页岩气吸附微观机理及主要影响因素。通过页岩等温吸附、直接降压解析、注CO2置换解析实验评价，提出了利用CO2分子置换页岩气吸附气提高采收率的新思路，不仅能提高页岩气的采收率,而且可以缩短开采周期，为探索页岩气的赋存机理和开采页岩气奠定基础。