民和盆地天然气地球化学特征

对民和盆地天然气地球化学特征进行研究，发现其天然气主要为煤层甲烷气和二氧化碳气，分析气源岩地球化学与天然气碳、氢、氧同位素，认为气源岩主要为中侏罗统窑街组的暗色泥岩、油页岩、藻煤、腐殖煤和炭质泥岩，其中暗色泥岩、油页岩、藻煤为Ⅰ-Ⅱ型干酪根，有机质丰度高；盆地煤层甲烷气为有机成因气，具有油型与煤型混合气特征，以油型气为主；煤层高浓度二氧化碳气不是有机成因气，也不是岩石化学热解无机成因气，而可能是与F19断裂带有关的深部无机成因气。甲烷气形成时间早，埋藏浅，大多逸散丢失而未形成气藏。CO₂气形成时间晚，来自深部，可以在合适的断层圈闭中聚集成藏。

GEOCHEMISTRY CHARACTERISTICS OF NATURAL GAS IN MINGHE BASIN

In order to forecast the oil gas exploration potential of Minghe Basin, the geochemistry characteristics of natural gas in the basin are studied and it is found out that the natural gas mainly consists of coalbed methane and CO2. By analyzing the geochemistry of the gas source rock and carbon isotope, hydrogen isotope, and oxygen isotope, it is considered that the gas source rock mainly consists of dark mudstone, shale, algal coal, humic coal and carbonaceous mudstone, among them, dark mudstone, shale and algal belong to types Ⅰ-Ⅱ kerogen with high organic matter abundance; the coalbed methane gas of the basin is organic origin gas with mixed gas characteristics of oil type gas and coal type gas, mainly being oil type gas; the CO2 with high concentration is neither organic origin gas nor the inorganic origin gas of rock chemo pyrolysis, but probably relating to the inorganic origin gas of deep fault F 19. Owing to over early forming and shallow burying, most of the methane scattered thus not forming gas reservoir. But the CO2 could be gathered to form reservoir in the suitable fault traps being due to forming late and from the deep.