煤层气解吸过程中甲烷碳同位素特征

煤层气地球化学的研究对象以甲烷为主。为了研究煤岩解吸的煤层气在解吸过程中发生碳同位素分馏作用,测试利用绳索取心煤岩样品在自主研发的煤层气/页岩气密封容器中连续解吸,每250 mL收集一次煤层气样品并进行碳同位素分析。实验结果表明:煤层气解吸前期,δ^13CPDB值基本上呈缓慢增加的趋势;当解吸气量增加到一定体积后,δ^13CPDB值迅速增高;解吸后期,δ^13CPDB值基本上又呈缓慢增加的趋势。在地面恒温解吸条件下,煤层气解吸的δ^13CPDB值随时间增加有逐渐增高的趋势,呈先慢后快再慢的过程。一般在煤层气解吸样品的同位素测试中,取解吸前期的气体进行测试,比实际同位素值稍微偏低。因此,在开展煤层气甲烷碳同位素在平面分布特征、成因和分馏机理等研究时需要适当考虑取样时间点这个因素。

Carbon isotope characteristics of methane during desorption of coalbed methane

The research is performed with core samples obtained by ropes,which was desorbed continuously within seal container,and carbon isotopic analyses were measured for the CBM samples collected per 250 mL one time. The result of test indicates:In earlier stage,δ^13CPDBCBM increases slowly;δ^13CPDBCBM increases quickly when the amount of desorption gas up to certain volume;In last stage,δ^13CPDBCBM became to increase slowly again. In the condition of constant temperature in the earth surface,δ^13CPDBof CBM desorption gas becomes heavy with increasing time,and it is characterized by a mode of slow,fast then slow. In common,the result for isotope testing of CBM desorption samples,it is slightly lower for the earlier desorption stage than the true isotope.