摘要
鄂尔多斯盆地侏罗系发育多层厚煤层,煤质优良,储量巨大,且构造简单,埋深较浅,具有很大的开采价值。该岩系独特的煤岩特征与其成煤沼泽环境有密切联系,即内陆湖泊发育有关的河流体系上部的一系列高位沼泽;泥炭埋藏后继续经历不同程度的氧化阶段,使得煤岩组分中惰性组分含量普遍偏高,而镜质组分普遍经受一定程度的丝炭化作用而成为半镜质体。研究表明盆地中侏罗系煤系中煤的宏观煤岩主要以半暗煤和暗淡煤为主,半亮煤和光亮煤占次要地位;在盆地边缘,特别是靠近盆地北部物源地区,半暗煤、暗淡煤含量比例较高,往南向盆地中心部位半亮煤和光亮煤逐渐增多,表明沉积环境和成煤沼泽环境对煤岩组分具有主要控制作用;含煤岩系中,特别是煤层下部砂岩越厚,颗粒越粗,显微煤岩组分中丝质体含量越高,而且其结构完整、清晰,半镜质体含量也越高,植物细胞结构越完整和规则。埋藏后顶底板岩性还会继续影响煤岩组分的演化过程。煤层顶底板砂体由于物性条件好,孔隙水仍可长时间处于氧化与循环流通状态,使得各煤岩组分能长时间处于氧化状态,有利于丝炭化作用进行;相反,在盆地中心,湖泊相发育,泥炭被埋藏之后迅速被泥岩覆盖,煤层很快处于还原缺氧环境,凝胶化作用得以充分进行,镜质组的含量就会增高。研究还发现,壳质组常常在煤层中的某一部位富集,虽然整个煤层中其平均含量不高,但是却对煤层的总体生烃能力会有很大贡献。以往的研究成果中,壳质组含量常常被低估,尤其是呈流动状态的沥青质体,因为它最容易流动到刚性比较强的丝质体内部或各种裂隙中而常常被忽略,在以后的研究中值得加以重视。
Multiple thick coal beds occur in Jurassic,Ordos basin.They have good coal qualities,huge reserves,simple structures,and relatively shallow burial depth.As a result,they possess large exploitation values.The characteristics of coal petrology are specific in Jurassic coal sequences in Ordos basin.Their genetic swamp environment was mainly a series of high-stand swamps on the upper fluvial system that was related with the development of typical inland lakes.The sand bodies were developed.The peat,after the burial,continued to undergo oxidation conditions with different degrees.As a result,the content of inert components is widely higher than normal values.The vitreous coal component had extensively undergone specific-degree fusainization and became semi vitrinite.The study shows that in Ordos basin,the coal petrology in Jurassic is mainly semidull coal and dull coal,and semilustrous coal and lustrous coal as follows.It is also found that the contents of semidull coal and dull coal have higher percentages in the basin margin,especially in the area near the provenance of northern basin;the semilustrous coal and lustrous coal become more and more southwards towards the central basin.This result explains that the depositional environment and coal-generating swamp environment have the major controlling effects on the coal components.Another result is that in these coal sequences,the fusinite content is higher in coal macerals with thicker sandstone and coarser grain sizes,moreover,its texture is complete and clear,especially in lower coal beds.The semi vitrinite has the same regularity.The cell texture of plants becomes more complete and regular.After the burial,the lithology of roof and floor rocks can continue to affect the evolution of coal petrology.The sand bodies in the roof and the floor of coal beds have good physical conditions so that the pore water can still be in the state of oxidizing,circulating and connecting in a long term.It makes the coal components stay in the oxidation phase for a long time,which is favorable for the process of fusinitization.On the contrary,the development of lacustrine facies and peat rapidly covered by mudstone after the burial swiftly,make the coal beds in reduction and anoxic environment.As a result,the gelatification can be done abundantly and the vitrinite content increases.Exinite often accumulates in a specific position of coal bed,and its average content is not high in the whole coal bed,but it has great contribution to the total hydrocarbon generated capacity of coal beds.In the past research results,the exinite content is often underestimated,especially amorphous bitumen in fluid state,for the reason that it is easiest to flow into the fusinite with strong rigidity or several fissures.The exinite content deserves to be emphasized in the further research.
出处
《现代地质》
CAS
CSCD
北大核心
2010年第6期1186-1197,共12页
Geoscience
基金
国家重点基础研究发展计划项目(2006CB202202)
国家自然科学基金项目(40772095,40972106)
长江学者和创新团队发展计划项目(IRT0864)
