低熟气地球化学特征与判识指标
收稿日期: 2009-11-20
修回日期: 2009-12-16
网络出版日期: 2010-02-10
基金资助
国家自然科学基金项目（编号：40703001）;油气重大专项（编号：2008ZX05008-001)联合资助.
Geochemical Characteristics and Identification Indexes of Low-mature Gases
Received date: 2009-11-20
Revised date: 2009-12-16
Online published: 2010-02-10
从目前的研究来看，低熟气的源岩母质类型主要以有机质丰度较高的Ⅲ型煤系为主。低熟气热演化程度（RO）值在0.4％～0.8％之间，根据煤型气CH4碳同位素组成与热演化程度RO之间的“二阶模式”关系，煤型气CH4碳同位素组成应该分布在-54‰～-39‰之间，目前发现的低熟气CH4碳同位素组成主要集中在-49‰～-39‰之间。一般认为煤型气的C2H6碳同位素组成重于-28‰，但是，当考虑低熟气时，将这一指标定为-29‰更为合适。根据煤型气CH4碳、氢同位素关系，低熟煤型气的CH4氢同位素组成分布在-300‰~-216‰之间. 天然气轻烃参数中，低熟煤型气的庚烷值分布在16％～22%之间，异庚烷值分布在2.2～5.0之间。生物气不仅在CH4、C2H6碳同位素组成上与低熟气存在明显的差别，同时在轻烃含量的参数上也存在明显的差别。
王晓锋, 徐永昌, 沈平, 郑建京, 史宝光 . 低熟气地球化学特征与判识指标[J]. 天然气地球科学, 2010 , 21(1) : 1 -6 . DOI: 10.11764/j.issn.1672-1926.2010.01.1
From the current studies, the coal measures with high organic matter are main types of source rocks of low-mature gases. The thermal evolution indices(RO) of low-mature gases should be within the range of about 0.4％~0.8％, and corresponding carbon isotope values of methane is within the range of about -49‰～-39‰ according the two-stage model of carbon isotope fractionation for coal\|type gases. It's generally believed that δ13Cethane value of coal-type gas is more than -28 ‰, however, when considering the low-mature gases, the value of -29‰ is more appropriate. According to relationship of carbon and hydrogen isotopic compositions of coal-type gases, the hydrogen isotopic composition of low-mature gases should be within the range of about -300‰~-216‰. Heptane value of low-mature gases are located in between 16%~22% and isoheptane value are in between 2.2～5.0. There exists an obvious difference between biogenic gas and low-mature gases not only in the carbon isotopic compositions of methane and ethane, but also in light hydrocarbon concentration.
Key words： Low-mature gases; Geochemistry; Stable isotope; Light hydrocarbon.
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