煤层CO2地质封存的微观机理研究

煤层CO₂地质封存可实现CO₂减排和增产煤层气双重目标，是一种极具发展前景的碳封存技术。相对于其他封存地质体而言，煤的微孔极其发育，煤层CO₂封存机制与煤中气、水微观作用关系密切，其内在影响机理尚不清楚。以2个烟煤样品的系统煤岩学分析测试为基础，构建了煤的大分子结构及板状孔隙空间模型，进一步采用分子动力学方法模拟了不同温、压条件下、不同煤基质类型表面的CO₂和水的润湿行为，揭示煤层CO₂注入后引起的水润湿性变化规律，初步阐明煤层CO₂封存的可注性、封存潜力、封存有效性等影响因素及微观作用机理。结果表明：(1)影响煤润湿性的主要因素是煤中极性含氧官能团，其含量越高煤的润湿性越强；(2)煤中注入CO₂后，CO₂通过溶解作用穿透水分子层与水分子发生竞争吸附，从而减小水在煤表面润湿性；(3)随注入压力增大和温度降低，煤表面CO₂吸附量增多，对氢键破坏作用增强，润湿性减弱越明显；(4)亲水性煤层CO<...

Micro-mechanism of geological sequestration of CO2 in coal seam

The geological sequestration of CO₂ in coal seam is a most promising carbon storage technology, which can help achieve the dual goals of CO₂ emission reduction and coalbed methane stimulation. Compared with other sealing geological bodies, coal has extremely well-developed micropores. The mechanism of geological sequestration of CO₂ in coal seam is closely related to the interaction of coal-gas-water. However, its internal influence mechanism is still unclear. Herein, the models of macromolecular structure and plat pore of the coals were constructed based on the systematic coal petrological analysis and testing of two bituminous coal samples. Meanwhile, the wetting behaviors of CO₂ and water on different coal-matrix surfaces at different temperatures and pressures were simulated using the molecular dynamics method. Thereby, the change rule of water wettability caused by the injection of CO₂ in coal seam was disclosed, and the influencing factors and microscopic mechanisms of injectability, storage potential and storage effectiveness of CO₂ in coal seam were preliminarily clarified. The results show that: (1) The main factor affecting coal wettability is the polar oxygen-containing functional groups in coal. Specifically, the higher the content of the oxygen-containing functional groups, the stronger the wettability of coal is. (2) The CO₂ injected into coal penetrates the water molecular layer through dissolution, and thus a competitive adsorption occurs with the water molecules, weakening the wettability of water on the coal surface. (3) With the increase of pressure and the decrease of temperature, the more CO₂ is adsorbed on the coal surface, and the more obvious the destruction of hydrogen bond and the decrease of wettability. (4) The hydrophilic coal seam has relatively poor injectability and storage potential of CO₂, but relatively good storage safety. (5) The CO₂ storage potential of coal seams are mainly influenced by the capacities of adsorption trapping and capillary trapping, while the effectiveness and security of storage are affected by the capacities of capillary trapping and structural trapping. (6) The sequestration of CO₂ in coal seam is mainly related to the adsorption trapping, taking capillary trapping under water-bearing conditions into account. The storage potential of high rank coal is higher than the low rank coal, but the “water block” effect needs to be overcome during CO₂ storage and injection. Moreover, the further study was conducted for the interaction of coal-gas-water and the geological sequestration mechanism of CO₂ in the deep coal seam under the in-situ conditions, which is of great significance for the development of CO₂-ECBM technology.