1. School of Geoscience and Surveying Engineering,China University of Mining and Technology ( Beijing),Beijing　 100083,China;2. School of Resources and Environment Engineering,Henan Institute of Engineering,Zhengzhou　 451191,China;3. Lanzhou Petroleum Resources Research Center,Institute of Geolo-gy and Geophysics,Chinese Academy of Sciences,Lanzhou　 730000,China

为了研究沁水盆地北部寺家庄太原组煤层甲烷（CH4）及二氧化碳（CO2）的成因,对11口煤层气井排采气进行了化学组分和同位素测试,探讨了煤层CH4及CO2的成因及联系。结果表明:沁水盆地北部煤层CH4平均体积分数为98.6%,CO2为0.25%,N2为1.07%;煤层CH4碳同位素值介于-33.2‰-40.8‰,平均值为-37.1‰,以煤热裂解成因为主,含有微生物CO2还原成因CH4,属于混合成因煤层气。沁北煤层CH4碳同位素分馏起主导作用的是解吸-扩散-运移作用,储层浅部压力小,含轻碳同位素的CH4优先解吸,经扩散运移至上部地层进而逸散到大气中。煤层CO2的δ13C值为-15.9‰+0.05‰,平均值为-8.6‰,为煤热演化初期或最近一次煤层抬升再沉降后煤中有机质热裂解产生,碳同位素较重的地方受地下水或微生物CO2还原作用影响。煤层CO2碳同位素随煤层埋藏变浅而变重,浅部煤层微生物CO2还原作用强,使CO2碳同位素变重。

A total of eleven coal seam gas (CSG) samples (production gases) were collected from the Taiyuan Forma- tion of Sijiazhuang District,Northern Qinshui Basin,China,and then their chemical and isotopic compositions were an- alyzed to study the origins of coalbed methane (CH4 ) and carbon dioxide (CO2 ). Results indicate that the CSG of Si- jiazhuang District is dominated by CH4(average:98. 6% ,air-free basis) with minor amounts of CO2(average:0. 25% ) and N2(average:1. 07% ). The δ13 C values of CH4 range from -33. 2‰ to -40. 8‰,with an average of -37． 1‰(n = 11),and CH4 was mainly generated from thermal cracking during coalification,with small proportion from microbial CO2 reduction. The desorption-diffusion-migration effect plays a dominant role in carbon isotope fractionation of CH4 . The CH4 with lighter carbon isotope in shallow reservoirs mainly desorbs from deep ones,then diffuses and moves to the upper part ( shallower reservoirs) and finally escapes into the atmosphere. The δ13 C values of CO2 are between -15． 9‰ and +0． 05‰,with an average of -8. 6‰,and the CO2 may be generated from thermal degration or thermal cracking or both at the early stage of coalification or after the latest coal seam uplift. The CO2 with heavier carbon iso- tope may be associated with groundwater or microbial CO2 reduction. The carbon isotopes of coalbed CO2 become heav- ier as the coal seam becomes shallower,because of the stronger CO2 reduction effect in shallower coal seam.

山西省煤层气联合基金资助项目(2013012005)；国家自然科学基金资助项目(41072119)；

Xu Zhanjie,Liu Qinfu,Zheng Qiming,et al. Origins and carbon isotopic composition of coalbed methane and carbon dioxide from Taiyuan Formation,Northern Qinshui Basin,China[J]. Journal of China Coal Society,2016,41(6):1467-1475.