鉴别生物成因气体主要地化指标的再认识

NEW UNDERSTANDING OF MAIN GEOCHEMICAL INDICATORS TO DISCRIMINATE BIOGENIC GAS

最近，俄罗斯地球化学工作者在汇总近25年来美国、欧洲和独联体等国家同行利用碳、氢同位素鉴别烃流体成因的资料时，对原来认为油气藏中甲烷碳、氢同位素及其不同埋深之间的变化规律有了一个新的认识。即：甲烷碳同位素较轻（δ13C（CH4）=-60‰～-70‰）的甲烷，不仅在地下浅部生成，也可在深部（达-4．5km）由烃流体决生变化而成。同时，这些气体的氢同位素也很轻（δD（CH4）＜-200‰）。他们认为深部成因的烃类气体和烃流体的分布比原来预计的要广泛得多，相应地，以前利用同位素资料确定天然气成因，以及据此结果进行的含油气性预测评价，均应进行适当的修正和补充。

Based on the research data about the genesis of hydrocarbon fluids by cardri and hydrogen isotopes in the United States, Europe and former USSR during the recent 25 years, theRussian geochemists have got sorn new understanding of the relationship among cadri andhydrogn isotopic comoposition of methane and depth of oil/gas reservoir, i.e., the methanewith light carbon isotope composition (δ13C(CH4) vdries betwee-60‰ and - 70‰) not only can be formed in shallow formtions but also in deeper part (depth to 4. 5 km) by the secondary alteration of hydrocarbon fluid. Meanwhile, this methane is typical of light hydrogeniwtope composition (δD＜ - 200%). Therefore, the Russian geochemists realized that the distribution of the deeply derived hydarbon gas and fluids is more wider than the considered originally. drisequently, the current metheds used to detendne the source of natural gas by isotope data and to evaluate the hych potential of a basin ought to be supplemented and revised.