扬子地区古生界泥页岩吸附性及控制机理

Adsorption capacity and controlling mechanisms of Paleozoic shales in Yangtze region

扬子地区古生界地层为富气泥页岩层系,是我国页岩气勘探开发的主战场。吸附态是页岩气最主要的赋存方式之一,该区泥页岩吸附性及控制机理的研究较为重要。采集了扬子地区古生界泥页岩样品,对其进行TOC测试、Rock-Eval、XRD及含水量分析、等温吸附实验、超高压等温吸附实验。结果表明,不同地区、不同时代泥页岩吸附性能产生差异的原因是有机碳含量、矿物成分及组成等主要因素综合作用的结果。实验过程中TOC含量与泥页岩甲烷吸附量并未呈现前人提出的正相关关系,这与泥页岩样品数量有限、且处于高—过成熟阶段的影响因素较多有关。古生界干酪根甲烷吸附曲线显示出时代越老的干酪根甲烷吸附能力越强的特征。去除有机质丰度和成熟度的影响,Ⅲ型干酪根的吸附量要高于Ⅱ型干酪根。在有机质丰度及类型相同的情况下,高成熟干酪根比低成熟干酪根具有更高的甲烷吸附量。可溶有机质具有较强的溶解吸附特征,能够增强原岩对甲烷的吸附能力。黏土矿物含量与经TOC含量归一化后的甲烷吸附量的相关关系并不明显,这主要与样品中普遍含水有关,同时样品的成熟度、孔隙度、渗透率等对其最大甲烷吸附量可能也会有影响。高压范围内的甲烷吸附特征与低压相比具有一定的延续性,影响因素较多,需要更深入的研究工作来揭示各单一因素对页岩高压吸附特性的影响。

As a gas-rich shale layer, the Paleozoic in Yangtze region is a main target for shale gas exploration and development in China. Adsorption state is one of the most important occurrence modes of shale gas;hence it is very necessary to study the adsorption capacity and controlling mechanisms of shales. We collected some shale samples from Paleozoic in Yangtze area, and then carried out TOC analysis, Rock-Eval, XRD and water content analyses, isother-mal adsorption experiments, and ultra-high pressure isothermal adsorption experiments. The adsorption properties of shales vary during different ages and in different areas due to the combined effects of TOC content and mineral compo-sition. The TOC content and methane adsorption of shales do not have a positive relationship as proposed by previous researchers, because that shale samples are limited and are in the high-mature and over-mature stages. The methane adsorption isotherms of kerogens in different ages show that older kerogens have a stronger methane adsorption capacity. Removing the effects of organic matter abundance and maturity, the kerogens of typeⅢadsorb more methane than those of typeⅡ. If organic matter abundance and type are the same, the methane adsorption amount of high matu-rity kerogen is more than that of low maturity kerogen. Soluble organic matter can dissolve and adsorb methane, and hence improve the methane adsorption capacity of shales. The relationship between clay mineral and methane adsorp-tion which is normalized by TOC is not obvious, this is mainly because the samples contain water.Maturity, porosity and permeability may affect the maximum methane adsorption of shales. Compared with low pres-sure, the methane adsorption characteristics under high pressure have a certain continuity. There are several influencing factors, which demand deep research to reveal the influence of each single factor on shale adsorption characteristics.