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页岩气地球化学异常与气源识别
引用本文:吴伟,房忱琛,董大忠,刘丹.页岩气地球化学异常与气源识别[J].石油学报,2015,36(11):1332-1340,1366.
作者姓名:吴伟  房忱琛  董大忠  刘丹
作者单位:1. 中国石油西南油气田公司勘探开发研究院 四川成都 610043; 2. 中国石油勘探开发研究院 北京 100083
基金项目:中国石油天然气股份有限公司科技专项(2014B-0608)资助。
摘    要:通过国内外页岩气生产井井口气的地球化学资料与常用的天然气鉴别指标的对比,认为部分页岩气的特征和传统的气源鉴别指标相比存在异常。其主要包括:页岩气乙烷碳同位素反转或倒转普遍存在于各套高过成熟的页岩系统,包括煤系地层;乙烷碳同位素鉴别气源的能力源于同位素反转,但高演化阶段煤成乙烷碳同位素可以很轻,甚至达到油型气标准;开放体系下的常规储层不一定能继承页岩系统的乙烷碳同位素及其倒转现象,常规的油型气乙烷碳同位素也可以很重;在极高的演化阶段,油型气存在乙烷碳同位素的第2次反转,甲烷氢同位素异常轻,甲烷碳同位素异常重,干燥系数极大,轻烃部分表现出煤成气的特征,常用的Bernard图版、Scholl图版和C7轻烃三角图都可能误判断为煤成气。常规天然气来自于烃源岩且能继承页岩气的诸多地球化学特征,该地球化学异常可能导致气源类型的错误判断,因此在常规天然气的鉴别过程中需引起重视。

关 键 词:页岩气  同位素倒转  气源鉴别  轻烃  油型气  煤成气  
收稿时间:2015-05-23
修稿时间:2015-09-30

Shale gas geochemical anomalies and gas source identification
Wu Wei,Fang Chenchen,Dong Dazhong,Liu Dan.Shale gas geochemical anomalies and gas source identification[J].Acta Petrolei Sinica,2015,36(11):1332-1340,1366.
Authors:Wu Wei  Fang Chenchen  Dong Dazhong  Liu Dan
Affiliation:1. Exploration and Development Research Institute, PetroChina Southwest Oil & Gasfield Company, Sichuan Chengdu 610041, China; 2. PetroChina Research Institute of Petroleum Exploration & Development, Beijing 100083, China
Abstract:Through a comparison between geochemical data of wellhead gas in domestic and overseas shale gas wells and commonly-used identification indices of natural gas, it is considered that anomalies exist in certain characteristics of shale gas as compared with the identification indexes of conventional gas source, mainly shown as below. The rollover or reversal of ethane carbon isotope in shale gas generally exists in highly or over matured shale systems, including coal measure strata. The ethane carbon isotope presents an ability of gas source identification derived from isotopic rollover, but in the high evolution stage, the coal-derived ethane isotope may become very light and reach the oil type gas standard. In an open system, the conventional reservoirs may not inherit the ethane carbon isotope and its reversal in shale system, while the ethane carbon isotope of conventional oil type gas can also be very heavy. In the ultra-high evolution stage, a second rollover of ethane carbon isotope can be detected in oil type gas, and the methane hydrogen isotope is abnormally light, while methane carbon isotope is abnormally heavy with extremely high aridity coefficient. The light hydrocarbon shows coal-derived gas characteristics, which might be misjudged as coal-derived gas according to commonly-used Bernard diagram, Scholl diagram and C7 light hydrocarbon triangular diagram. Conventional natural gas is derived from source rocks, and has inherited the multiple geochemical characteristics of shale gas. This geochemical "anomaly" could lead to misjudgment of gas source types, which should be paid more attentions in the identification process of conventional natural gas.
Keywords:shale gas  isotope reversal  gas source identification  light hydrocarbon  oil type gas  coal-derived gas  
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