Zhou Wenning, Zhang Zhe, Wang Haobo, Yang Xu
School of Energy and Environmental Engineering, University of Science and Technology Beijing, Beijing 100083, China.
Beijing Key Laboratory of Energy Saving and Emission Reduction for Metallurgical Industry, University of Science and Technology Beijing, Beijing 100083, China.
Nanomaterials (Basel). 2019 Nov 20;9(12):1646. doi: 10.3390/nano9121646.
The adsorption behavior and the mechanism of a CO/CH mixture in shale organic matter play significant roles to predict the carbon dioxide sequestration with enhanced gas recovery (CS-EGR) in shale reservoirs. In the present work, the adsorption performance and the mechanism of a CO/CH binary mixture in realistic shale kerogen were explored by employing grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations. Specifically, the effects of shale organic type and maturity, temperature, pressure, and moisture content on pure CH and the competitive adsorption performance of a CO/CH mixture were investigated. It was found that pressure and temperature have a significant influence on both the adsorption capacity and the selectivity of CO/CH. The simulated results also show that the adsorption capacities of CO/CH increase with the maturity level of kerogen. Type II-D kerogen exhibits an obvious superiority in the adsorption capacity of CH and CO compared with other type II kerogen. In addition, the adsorption capacities of CO and CH are significantly suppressed in moist kerogen due to the strong adsorption strength of HO molecules on the kerogen surface. Furthermore, to characterize realistic kerogen pore structure, a slit-like kerogen nanopore was constructed. It was observed that the kerogen nanopore plays an important role in determining the potential of CO subsurface sequestration in shale reservoirs. With the increase in nanopore size, a transition of the dominated gas adsorption mechanism from micropore filling to monolayer adsorption on the surface due to confinement effects was found. The results obtained in this study could be helpful to estimate original gas-in-place and evaluate carbon dioxide sequestration capacity in a shale matrix.
页岩有机质中CO/CH混合物的吸附行为及机理对于预测页岩气藏中强化采气的二氧化碳封存（CS-EGR）具有重要作用。在本工作中，采用巨正则蒙特卡罗（GCMC）和分子动力学（MD）模拟方法，研究了实际页岩干酪根中CO/CH二元混合物的吸附性能及机理。具体而言，研究了页岩有机类型和成熟度、温度、压力以及含水量对纯CH4和CO/CH混合物竞争吸附性能的影响。研究发现，压力和温度对CO/CH的吸附容量和选择性均有显著影响。模拟结果还表明，CO/CH的吸附容量随干酪根成熟度的增加而增大。与其他II型干酪根相比，II-D型干酪根在CH4和CO的吸附容量上表现出明显优势。此外，由于H2O分子在干酪根表面的强吸附作用，潮湿干酪根中CO和CH4的吸附容量显著降低。此外，为了表征实际干酪根的孔隙结构，构建了一种狭缝状干酪根纳米孔。研究发现，干酪根纳米孔在确定页岩气藏中CO地下封存潜力方面起着重要作用。随着纳米孔尺寸的增加，由于限域效应，气体吸附主导机制从微孔填充转变为表面单层吸附。本研究所得结果有助于估算页岩基质中的原始天然气储量并评估二氧化碳封存能力。
