决定煤层气地球化学特征的关键地质时期

KEY GEOLOGICAL TIME OF DECIDING THE GEOCHEMICAL CHARACTERISTICS OF COALBED METHANE

文章在地温梯度、埋藏史研究的基础上,探讨沁水盆地煤层的热演化过程及其对煤层气地球化学特 征的控制作用。通过对沁水盆地南部阳城地区和西部霍州地区的煤层热演化史和煤层气地化特征的对比研究表 明,演化程度最高的地质时期决定了煤层气的组份和组份碳同位素特征,即是决定煤层气地球化学特征的关键地 质时期,如沁水南部晋城地区的3#煤层在早白垩世末的Ro值达到2.4%～4.2%的最大值,从而形成甲烷碳同位素 分布为-29.9‰～-36.7‰的煤层气;三叠系末期,霍州地区2#煤层处于成熟阶段(Ro=0.8%～1.2%),决定了 该地区煤层气甲烷碳同位素分布为-47.6‰～-51.7‰。反之,煤层气的组份和组份碳同位素特征也反映了煤层 所经历的热演化过程。

On the basis of studying geothermal gradient and burial history, the thermal evolution course of the coal beds in Qinshui Basin and its control effect on geochemical characteristics of the coalbed methane in the basin are discussed in the paper. Through the contrast research on the thermal evolution histories of coal beds and the geochemical characteristics of coalbed methane in Yangcheng region of south Qinshui Bosin and in Huozhou region of west Qinshui Basin, it was indicated that the component and its carbon isotope characteristics were decided during the geological time of the highest evolution degree, i.e. the key geological time of deciding the geochemical characteristics of coalbed methane. For example, the R o value of coal bed No.3 in Jincheng region of south Qinshui Basin reached to its maximum of 2.4%—4.2% at the end of Early Cretaceous, thus forming the coalbed methane with methane carbon isotope ratios of -29.9‰—-36.7‰ and, at the end of Triassic, the coal bed No.2 in Huozhou region was in the mature stage with R o values of 0.8%—1.2%, methane carbon is otope ratios being -47.6‰—-51.7‰. Therefore the thermal evolution course experienced by the coal beds can be reflected by coalbed methane component and its carbone isotope characteristics.