煤系页岩矿物组成特征与含气量关系探析

Analysis on the Relationship between Mineral Composition Characteristics and Gas Content of Coal-measure Shale

为了解页岩内部矿物组成特征与含气量之间的关系,对取自山西沁水盆地南缘煤系页岩钻井样品进行了岩相光学鉴定和真空电磁脱气试验,获取到页岩各矿物组分比例特征和含气量、气体化学组成等较多地质、地球化学信息。在对其进行对比分析后显示:该区域页岩矿物组成种类较为完整丰富,脆性矿物以石英、碳酸盐类、长石等为主,含量较高,占到矿物组成总体积的80%以上,且晶体形态较完整,说明本区域原始沉积环境有利于脆性矿物的生成和保存;黏土矿物含量较低,主要以低变质程度下的伊利石为主,并未对岩石内部通道造成实质阻塞,且发育有塑性微裂缝;大量脆性矿物的存在为页岩内部孔隙空间的发育和页岩气运移流动提供了便利;代表性矿物在垂向上呈一定序列分布,结合岩样含气量及气体化学组分观察,显示释出的烃类及CO_(2)含量与两大类型矿物组合呈现此消彼长的关系;且发现页岩中长石含量各向异性变化可在一定程度上逆转矿物组成与含气量的线性表现。

In order to understand the relationship between mineral composition characteristics and gas content in shale,the lithofacy optical identification and vacuum electromagnetic degassing test of the coal-measure shale drilling samples taken from the southern margin of Qinshui Basin in Shanxi Province were carried out,and various mineral groups of shale were taken.There are many geological and geochemical information such as proportion characteristics,gas content and gas chemical composition were obtained.The comparative analysis shows that the shale mineral composition in this area is relatively complete and rich,and the brittle minerals are mainly quartz,carbonates,feldspar,etc,with high content,accounting for more than 80%of the total volume of mineral composition.The crystal morphology is relatively complete.It indicates that the original sedimentary environment in this area is conducive to the generation and preservation of brittle minerals.The content of clay minerals is low,mainly based on illite at low metamorphism degree,and there are plastic micro-fractures,which do not affect the rock.Internal channels cause substantial blockage.The presence of a large number of brittle minerals facilitates the development of pore space in shale and the migration and flow of shale gas.Representative minerals are vertically distributed in a certain sequence,combined with the gas content of rock samples and gas chemical groups.Different observations show that the released hydrocarbon and CO_(2) content and the combination of the two types of mineral assemblages show a trade-off relationship.Moreover,it is found that the anisotropic change of feldspar content in shale can reverse the linear performance of mineral composition and gas content to a certain extent.