张家口宣东矿辉绿岩床对煤层气赋存的影响

The influence of diabase on the occurrence of coalbed methane in Zhangjiakou Xuandong mine

张家口宣东矿是一个高瓦斯矿井。为了查明矿井煤层气赋存规律及其变化原因,通过大量勘查钻孔及井巷揭露资料,深入研究了辉绿岩体侵入时代、产状特征及空间分布,分析了煤层煤质及煤层气变化规律,探讨了辉绿岩对煤层气的影响。结果表明:宣东矿辉绿岩以岩床形式侵入到侏罗纪下花园煤系中,导致本区异常古地热力场的形成,促使煤层发生区域热变质作用;煤的热演化变质作用是其发生二次生烃演化的直接原因,而这种生烃作用是影响本区煤层含气性的关键因素,它促进了煤层气的形成,且本区煤类及煤层气的分布特征与辉绿岩床的赋存特征很吻合;辉绿岩床形成良好的盖层,封闭了煤层气的逃逸通道,对煤层气的后期保护和富集提供了条件。

Zhangjiakou Xuandong mine is a high gassy mine. For finding out the occurrence regularity of coal mine methane and its cause of formation, this paper consults a large number of data exposed by investigation boreholes and roadways, studies intensively the intrusion age, occurrence characteristics and spatial distribution of diabase, analyzes the varying pattern of coal seam, coal quality and coal bed gas, discusses the influence of diabase on coal bed gas. Interrelated analyses conclude that Xuandong Diabase intrudes into Jurassic Xiahuayuan coal measure strata in the form of bed rock, resulting in abnormal geothermal fields and regional thermal metamorphism of coal bed in the study area. The thermal metamorphism of coal is the direct cause for the secondary hydrocarbon generation. This kind of hydrocarbon generation is the most important factor for current gas content, playing decisive role on the generation of coalbed gas. The distribution characteristics of coal and coal bed gas in this area are highly consistent with the occurrence characteristics of diabase bed. Diabase bed is a good caprock which blocks the escape route of the gas. The bed rock provides conditions for the protection and enrichment of the gas.