中国煤层甲烷稳定碳同位素分布与成因探讨

Characteristics and Origins of Stable Carbon Isotope in Coalbed Methane of China

在系统总结我国煤层甲烷稳定碳同位素的地域、时域和煤级分布特征的基础上，对其成因进行了探讨，研究表明：我国煤层气稳定碳同位素具有分布范围广、同位素组成偏轻的总体特点，在进入无烟煤阶段之后煤层甲烷δ13C1开始接近或落入腐殖型常规天然气甲烷稳定同位素分布范畴，煤层一次脱气的δ13C1轻于二次脱气；我国大部分地区中－高煤级煤储层中现存煤层气碳同位素分布主要受控于热动力学机制之下的同位素分异，解吸－扩散－运移分馏效应在此背景之上的叠加，可能是导致煤层甲烷碳同位素偏轻的主要原因。

The distribution of the stable carbon isotope of coalbed methane (CBM) in China was systematically generalized in the aspects of area, geological era, and coal rank. The origin of CBM was discussed. In general, the carbon isotope is more extensively distributed and lighter in composition than that of the normal natural gas, and approaches to or falls in the range of the normal humic-type gas during the anthracite period.The δ13C1 in the CBM from the first stage of desorption is lighter than that from the secondary stage. The carbon isotope composition of the CBM in the middle-high rank coal reservoirs from most parts of China is controlled mainly by the isotope fractionation under the thermodynamical mechanism, and the addition of the CBM desorption- diffusion-migration effect to the mechanism might be the important reason why the carbon isotope is relatively light.