煤层气碳同位素阶段演化的模拟实验研究及其应用

煤层气聚集存在着“累积聚气”和“阶段聚气”两种形式。通过热模拟实验，研究了“阶段聚气”的煤层气甲烷碳同位素的的影响因素和不同成熟度区间煤层气甲烷碳同位素组成特征。结果表明，“阶段聚气”的煤层气碳同位素组成与该演化阶段的起始Ro值和末尾Ro值密切相关，起始和末尾Ro值越高，煤层气碳同位素组成越重；相同成熟度区间，高升温速率下形成的煤层气碳同位素组成比较轻；煤岩母质性质影响煤层气碳同位素组成；在相同成熟度区间，泥炭形成的甲烷碳同位素组成最轻。确定了成煤有机质从Ro为1.2％、1.6％、2.0％、2.4％、2.8％分别演化至Ro为3.0％和4.0％(3.7％)之间生成的煤层气甲烷碳同位素组成，这为研究不同成熟度区间生成的煤层气成因提供了科学数据。并且，将这些研究结果应用到沁水盆地南部煤层气研究，认为该地区煤层气是在中侏罗世末以后（Ro＞1.6％）聚集而成，具有“阶段聚气”的特征。

Thermal Simulation Experiment and Application of Staged Evolution of Coalbed Methane Carbon Isotope

Coal bed methane (CBM) accumulation models include continuous gas accumulation and staged gas accumulation. In this paper, the influence factors of carbon isotope of CBM formed by staged gas accumulation and carbon isotopic composition of CBM formed in different maturity intervals were researched by thermal simulation experiment. The results showed that the carbon isotopic composition of CBM formed by staged gas accumulation is related to initial Ro and final Ro values in the evolutionary stage. With the increase of initial Ro and final Ro values, carbon isotope of CBM became heavier. In some maturity intervals, the carbon isotopic composition of CBM formed at higher heating rate was lighter than that at lower heating rate. At the same time, nature of coal also affects carbon isotope of CBM. The carbon isotope of methane generated by peat was the lightest of all three samples. The carbon isotopic composition of CBM formed by coal parent material with Ro  values of 1.2%, 1.6%, 2.0%, 2.4% and 2.8% rising to 3.0 and 4.0%, respectively, was determinated. This provides scientific evidence for studying the genesis of CBM generated in different maturity intervals. These results were used to study CBM from the southern Qinshui basin, and it is found that CBM from the southern Qinshui basin was accumulated after terminal Middle Jurassic (Ro >1.6%) and characterized by the staged gas accumulation.