腐泥型有机质纳米孔隙结构演化特征及吸附甲烷能力研究

Large numbers of experimental studies have been carried out on the pore structure and the adsorption characteristics of humic coal which is mainly composed of humic organic matters. These studies gained the systematic understanding of the pore structure and the adsorption characteristics of humic coal and promoted the development of CBM industry powerfully. Marine or continental black shale, whose organic matter type is sapropel or partial mixed sapropel, is the main selectable district of shale gas. However, because of the lower abundance of organic matters, it is very difficult to study the pore structure and the adsorption characteristics of sapropelic organic matters in shale. Therefore, there are no systematic or comprehensive research results on shale till now. The sapropelic coal formed in oceans, lakes or deeper water marshes, has the similar forming environment and material components with the shale gas reservoirs. However, the content of organic matters in the sapropelic coal is much higher, which provides favorable conditions for systematically evaluating the pore structure and the adsorption characteristics of sapropelic organic matters. This project was planned to analyze the nano-pore structure characteristics and the evolution of sapropelic organic matters, through systematically carrying out the tests on the pore structure of sapropelic coal and its isothermal adsorption experiments. Meanwhile, to reveal its adsorptive capacity to methane and also to discuss the influence factors to adsorptive capacity, for example, temperature, pressure, the components, contents and maturity degree of organic matters, etc. The research achievement will have important reference value on the scientific evaluation of shale gas resource potential and its exploiting mechanism.

对于以腐殖型有机质为主要成分的腐殖煤的孔隙结构及吸附特性已开展过大量实验研究，获得了较系统的认识，有力地推动了煤层气产业的发展。海相或陆相黑色页岩是页岩气选区的重要领域，其有机质类型以腐泥型或偏腐泥型的混合型为主。但由于页岩中有机质丰度较低，造成了有关页岩中腐泥型有机质孔隙结构及吸附特性研究难度较大，研究成果还远没有达到系统和完善。形成于海洋、湖泊或较深水沼泽中的腐泥煤，与页岩气储层具有相似的形成环境和物质组成，但其中有机质含量要高得多，为系统评价腐泥型有机质的孔隙结构及吸附性能提供了有利条件。本项目拟通过系统开展腐泥煤的孔隙结构测试及等温吸附实验，分析腐泥型有机质纳米级孔隙结构特征及演化规律，揭示腐泥型有机质对甲烷的吸附能力，并探讨温度、压力、有机质组分、含量及成熟度等因素对腐泥型有机质吸附甲烷能力的影响。项目成果将对科学评价页岩气资源潜力和开发机理具有重要参考价值。

采用多种有效手段系统开展了腐泥煤与海相黑色页岩的孔隙结构观测及等温吸附实验，分析了腐泥型有机质纳米级孔隙结构特征及演化规律，揭示了腐泥型有机质对甲烷的吸附能力，并探讨了黑色页岩中有机质类型、含量、成熟度以及黏土矿物种类与含量等因素对其吸附甲烷能力的影响。研究结果表明，腐泥煤的孔隙类型多样，其孔隙体积综合分形维数与孔隙总体积呈正相关关系，孔隙比表面积分形维数与孔隙度有微弱的正相关关系，与灰分呈负相关关系，变质作用对腐泥煤的孔隙结构起到了均一化的作用。湘西北下古生界黑色页岩的储集空间类型主要分为矿物基质孔、有机质孔、微裂缝3大类，原始的沉积环境与成岩过程控制着泥页岩中孔隙和微裂缝系统发育特征，不同的成岩阶段控制着页岩中孔隙结构的演化过程，进而影响着页岩气的赋存状态。基于低温氮吸附实验的比表面积分形维数与BET表面积成正相关关系，与BJH总孔容和平均孔径成负相关关系；体积分维数与BET比表面积和BJH总孔容成负相关关系，与平均孔径成正相关关系。有机质成熟度与比表面分维数Db和体积分维数Dt均呈负相关关系。低煤阶腐泥煤的兰氏体积大于高煤阶腐泥煤。干酪根的甲烷吸附能力依次为III型干酪根> II型干酪根>I型干酪根。Ⅰ型干酪根样品单位质量的最大甲烷吸附量远高于纯黏土矿物和黑色页岩样品，约为伊利石等粘土矿物的3～5倍。随着有机质成熟度增高其吸附能力逐渐增加，但当Ro>3.0%之后其吸附能力出现下降趋势。随着温度的升高，干酪根对甲烷的最大吸附量成线性递减，水分对干酪根吸附甲烷能力影响不大。粘土矿物中蒙脱石的甲烷吸附量最高，其次是高岭石、伊利石和伊蒙混层，绿泥石的吸附容量最小。粘土矿物对页岩吸附容量的贡献不可忽视。项目成果对于揭示腐泥型有机质孔隙结构演化特征及其储气机理奠定了重要基础，同时对于科学评价页岩气资源潜力和开发机理也具有重要参考价值。