Abstract:

Adding wetting agent to water is an effective method to improve the wetting effect of coal bed water injection. Taking coal samples with different degrees of metamorphism as the research object, a combination of macroscopic experiments, mesoscopic experiments and microscopic molecular dynamics simulations was used to explore the effects of compound surfactants on the wettability of different coal types. Firstly, surface tension and contact angle experiments were used to evaluate the effects of different compounding ratios of surfactants on the wettability of the three coal samples from a macroscopic point of view and to determine the optimal compounding method. The results showed that the best wetting effect was achieved when sodium laureth sulfate (SLES) and aliphatic alcohol ethoxylate (AEO-9) was compounded at a mass ratio of 3∶2. Secondly, mesoscopic experiments such as scanning electron microscopy and Fourier transform infrared spectroscopy were used to further investigate the wettability and adsorption capacity of the composite surfactants on different coal samples. The results indicated that after treatment with the composite solution, agglomerated bulk coal particles would be formed on the coal surface and the cracks between the coal particles were conducive to the penetration of the aqueous solution to wet the coal seam. At the same time, the total content of hydrophobic groups in coal molecules was significantly reduced, the content of hydrophilic functional groups was significantly increased and the aggregation ability between coal particles was enhanced, which was conducive to dust deposition. Finally, the wetting synergistic mechanism of composite surfactants on different systems was analyzed from the perspective of microscopic molecular simulation. The results showed that the composite surfactant molecules can be well adsorbed on the surface of coal molecules, promote the movement of a large number of water molecules to the coal surface, improve the interaction energy at the interface between coal and water, enhance the thickness of the water molecule layer on the coal surface and increase the diffusion coefficient of water molecules. The research results were of great significance to improve the wettability of coal.

Key words: different coal types, complex surfactants, functional groups, wettability, molecular dynamics simulation

摘要：

在水中添加润湿剂是提高煤层注水润湿效果的有效方法。以不同变质程度煤样为研究对象，采用宏观实验、介观实验以及微观分子动力学模拟相结合的方法，探讨复合表面活性剂对不同煤种润湿性的影响。首先，利用表面张力和接触角实验从宏观角度评估不同复配比例表面活性剂对三种煤样润湿性的作用，确定最佳复配方法。结果表明，月桂醇聚醚硫酸酯钠（SLES）与脂肪醇聚氧乙烯醚（AEO-9）以质量比为3∶2复配时润湿效果最佳。其次，利用扫描电子显微镜、傅里叶变换红外光谱等介观实验进一步研究复合表面活性剂对不同煤样的润湿性和吸附能力。结果表明，复合溶液处理后，煤表面会形成团聚的大块煤颗粒，煤颗粒间的裂缝有利于水溶液渗透润湿煤层。同时，煤分子中疏水基团总含量显著降低，亲水性官能团的含量明显增加，煤颗粒之间聚集能力增强，有利于粉尘沉降。最后，从微观分子模拟的角度分析了复合表面活性剂对不同体系的润湿协同机理。结果表明，复合表面活性剂分子能很好地吸附在煤分子表面，促进大量水分子向煤表面移动，提高煤与水界面的作用能，增强煤表面水分子层的厚度，增加水分子的扩散系数。研究结果对改善煤的润湿性具有重要意义。

关键词: 不同煤种, 复合表面活性剂, 官能团, 润湿性, 分子动力学模拟