中国煤层气成藏的两大关键地质因素

TWO KEY GEOLOGICAL FACTORS CONTROLLING THE COALBED METHANE RESERVOIRS IN CHINA

煤层气是一种非常规天然气,与常规天然气的主要差异在于地下的赋存形式和成藏机理不同。煤层气藏的形成除了与气源和储集等自身条件有关外,更重要的是与后期保存条件密切相关,而构造演化和水动力条件是煤层气保存的两大关键地质因素。指出:现今埋深相同的煤层,因为其经历的回返抬升时间的早晚、长短及抬升的程度不同,现今煤层气的富集程度也不同,抬升后期一直处于隆起剥蚀的地区,煤层气将不断散失,而发生沉降的地区则有利于煤层气的保存,但易造成煤层气饱和度的降低;煤系中流动的地下水对煤层气的含量和地球化学特征影响很大,在平面上和剖面上,水动力条件强的地区,煤层气的含量小、甲烷碳同位素轻。

The forming of coaled methane reservoirs correlate with the self-conditions of coal beds, and more important with the later preservation conditions among which the tectonic evolution and hydrodynamic condition are the key geological factors. The accumtilation and enrichment is quite different in coal beds even with the same buried depth if they had experienced different tectonic evolution process including the beginning and lasting time, and the intensity of reversing and uplifting. The CBM constantly the preservation of CBM, but also can lead to the reduction of CBM saturation. The flowing ground water affects coalbed gas content and geochemical characteristics obviously. In both horizontal and vertical plane, the coal has a lower gas content and a lithter carbon isotope of coalbed methane in the area of stronger hydrodynamics.