石油与天然气地质 ›› 2009, Vol. 30 ›› Issue (5): 519-529.doi: 10.11743/ogg20090501

• 专家论坛 •    下一篇

四川盆地须家河组煤系烷烃气碳同位素特征及气源对比意义

戴金星1, 倪云燕1, 邹才能1, 陶士振1, 胡国艺1, 胡安平2, 杨春1, 陶小晚1   

  1. 1. 中国石油 勘探开发研究院,北京 100083;
    2. 浙江大学 地球科学系,浙江 杭州 310027
  • 收稿日期:2009-05-26 出版日期:2009-10-25 发布日期:2012-01-16

Carbon isotope features of alkane gases in the coal measures of the Xujiahe Formation in the Sichuan Basin and their significance to gas-source correlation

Dai Jinxing1, Ni Yunyan1, Zou Caineng1, Tao Shizhen1, Hu Guoyi1, Hu Anping2, Yang Chun1, Tao Xiaowan1   

  1. 1. PetroChina Exploration and Development Research Institute, Beijing 100083, China;
    2. Department of Earth Sciences, Zhejiang University, Hangzhou, Zhejiang 310027, China
  • Received:2009-05-26 Online:2009-10-25 Published:2012-01-16

摘要:

四川盆地上三叠统须家河组煤系是套陆相含煤地层。须家河组一、三、五段以暗色泥岩和煤为主,是气源岩。泥岩干酪根以Ⅱ型和Ⅲ型为主,有机碳含量平均为1.96%,在川中处于成熟阶段,在川西处于高成熟阶段。由于源岩以腐殖型为主,故以形成气为主,气中仅有少量轻质油或凝析油。须家河组二、四、六段以砂岩为主,故有3套生储盖组合,形成许多自生自储煤成气田。在四川盆地须家河组发现的天然气储量仅次于下三叠统飞仙关组,并有该盆地第二大气田(广安气田)。须家河组煤成气碳同位素特征:一是绝大部分具有正碳同位素系列,即δ13C113C213C313C4;二是δ13C2值是全盆地9个产气层系中最重的,为-20.7‰~-28.3‰;三是川中地区有一批轻的δ13C1值,最轻为-43.0‰。在川东和川南须家河组变薄的地区还发现少量油型气藏,这些气藏碳同位素特征是δ13C2值轻,一般轻于-30‰,最轻为-36.3‰,易与煤成气区分。

关键词: 碳同位素, 气源对比, 烷烃气, 须家河组, 四川盆地

Abstract:

The coal measures in the Upper Triassic Xujiahe Formation in Sichuan Basin are coal-bearing continental strata.Its first,third,and fifth members are dominated by dark mudstone and coal and are gas source rocks.The kerogen of the mudstone are mainly of type Ⅱand Ⅲ with an average TOC of 1.96%.They are mature in the central Sichuan Basin and are highly mature in the western Sichuan Basin.Since the organic matter of source rocks are dominated by huminite,the source rocks are gas prone and the gas generated only contains minor light oil or condensate.The second,fourth and sixth members consist mainly of sandstone.There are three sets of source-reservoir-caprock combinations,resulting in many indigenous coal-derived gas fields.The gas reserves discovered in the Xujiahe Formation is only next to that in the Lower Triassic Feixianguan Formation.The Guangan gas field,the second largest gas field in the basin,produce gas from the Xujiahe Formation.The carbon isotope of the coal-derived gas have the following features:1) most of them are positive carbon isotopes(i.e.,δ13C113C213C313C4),2) its δ13C2 value is between-20.7‰--28.3‰,the heaviest among that of the 9 gas pays in the whole basin,3) there are lighter δ13C1 in central Sichuan Basin with the lowest value of-43.0‰.A few gas reservoirs sourced from oil-prone kerogens had been discovered in eastern and southern Sichuan Basin,where the Xujiahe Formation thins out.These reservoirs have light carbon isotopes(typically lighter than-30‰,and in extreme cases as light as-36.3‰) and can be easily distinguished from coal-derived gases.

Key words: carbon isotope, gas-source correlation, alkane gas, Xujiahe Formation, Sichuan Basin

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