天然气地球科学 ›› 2020, Vol. 31 ›› Issue (7): 931–938.doi: 10.11764/j.issn.1672-1926.2020.05.006

• 天然气地球化学 • 上一篇    下一篇

压力对III型有机质生成烃类气体及甲烷碳同位素的影响

何春民1,2(),甘军3,梁刚3,李兴3,王星1,2,田辉1()   

  1. 1.中国科学院广州地球化学研究所地球化学国家重点实验室, 广东 广州 510640
    2.中国科学院大学, 北京 100049
    3.中海石油(中国)有限公司湛江分公司, 广东 湛江 524057
  • 收稿日期:2020-01-30 修回日期:2020-04-30 出版日期:2020-07-10 发布日期:2020-07-02
  • 通讯作者: 田辉 E-mail:hechmin@mail2.sysu.edu.cn;tianhui@gig.ac.cn
  • 作者简介:何春民(1992-),男,湖北荆州人,博士研究生,主要从事油气地球化学与石油地质学研究.E-mail: hechmin@mail2.sysu.edu.cn.
  • 基金资助:
    国家科技重大专项(2016ZX05026-002-005);广东省自然科学基金“南方下古生界富有机质页岩孔隙结构演化研究”(2016A030310119)

The influence of pressure on hydrocarbon gas generation and carbon isotope of methane from type III kerogen

Chun-min HE1,2(),Jun GAN3,Gang LIANG3,Xing LI3,Xing WANG1,2,Hui TIAN1()   

  1. 1.State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
    2.University of Chinese Academy of Sciences, Beijing 100049, China
    3.Zhanjiang Branch, CNOOC China Ltd. , Zhanjiang 524057, China
  • Received:2020-01-30 Revised:2020-04-30 Online:2020-07-10 Published:2020-07-02
  • Contact: Hui TIAN E-mail:hechmin@mail2.sysu.edu.cn;tianhui@gig.ac.cn
  • Supported by:
    China National Science and Technology Major Project(2016ZX05026-002-005);Guangdong Natural Science Foundation(2016A030310119)

摘要:

以琼东南盆地崖城组海陆过渡相烃源岩为例,开展了50 MPa、100 MPa和150 MPa下的生烃模拟实验,初步探讨了压力对烃类气体生成与碳同位素分馏的影响。实验结果表明:压力的增加在热解温度较低时(等效镜质体反射率低于2.69%)可抑制烃类气体生成,并且压力对湿气组分的抑制作用比甲烷更明显;在较高热解温度下(等效镜质体反射率高于2.77%)压力的作用不明显或略微促进甲烷生成。烃类气体生成动力学参数拟合结果表明,压力增大在提高反应活化能的同时也增大了频率因子,这是因为在封闭黄金管热模拟实验体系中压力的增大使得气体膨胀克服压力做功增加的同时也使得反应物浓度增大。在5 oC/Ma的升温速率下,从50 MPa增大到150 MPa,每增加50 MPa进入生气窗温度大约升高10 oC,当温度高于260 oC后压力作用不再明显。实验结果还表明,相同热解温度下压力增大使甲烷更富集12C1,从50 MPa增大到150 MPa,甲烷碳同位素组成最大变轻幅度可达3.2‰。同时,不同压力下甲烷的转化率与碳同位素关系并非完全一致,说明压力促使甲烷碳同位素组成变轻并非完全通过抑制甲烷的生成实现,还可能与压力增大使得甲烷生成机制发生了轻微变化,进而造成13C112C1生成活化能之差发生改变有关。

关键词: 琼东南盆地, 烃类气, 甲烷碳同位素, 生烃动力学, 超压

Abstract:

Samples from transitional source rocks of Qiongdongnan Basin were pyrolyzed under 50 MPa, 100 MPa and 150 MPa, in order to tentatively discuss the effects of pressure on hydrocarbon gas generation and carbon isotope fractionation of methane. The results presented that increasing pressure would retard the hydrocarbon gas yield when pyrolytic temperature was low (EqVRO% less than 2.69%), and when it came to wet gases, the retardation was more significant than methane. However, there would be little influence of pressure at high pyrolytic temperature (EqVRO% more than 2.77%), or even slightly promoting methane generation. Calculated kinetic parameters showed that activation energy and frequency factor increased with growing pressure, as a result of that growing pressure makes the gas in the closed gold tube expand to do more work as well as the reactant concentration enrichment. At the rate of 5 ℃/Ma, pressure increases from 50 MPa to 150 MPa, which will result in the temperature increase of about 10 ℃ for every 50 MPa in the gas window. When temperature is higher than 260 ℃, the effect of pressure is no longer obvious. The experiment results also presented that growing pressure makes methane rich in 12C1. And it could result in 3.2‰ negative shift of carbon isotope values from 50 MPa up to 150 MPa. Meanwhile, the relationships between carbon isotope values and methane conversion were not the same under different pressures, indicating that negative shift of methane carbon isotope value was not only related to the retardation of methane generation, but also related to the slight changes happened to methane generation mechanism, which resulted in the changes in the distribution of the difference of activation energy between 13C1 and 12C1.

Key words: Qiongdongnan Basin, Hydrocarbon gases, Carbon isotope value of methane, Kinetics, Overpressure

中图分类号: 

  • TE122.1+13

表1

YC13-1-2井崖城组泥岩及对应干酪根样品基础地球化学参数"

样品类型深度/m层位沉积相

TOC

/%

S2/(mg/g)

IH

/(mg/gTOC)

Tmax

/oC

RO/%δ13Corg/‰

干酪根

类型

泥岩3 989~4 014崖城组海陆过渡相11.213.3118.74611.05-27.3III
干酪根3 989~4 014崖城组海陆过渡相64.481.8127.0462--27.5III

图1

不同压力下YC13-1-2井崖城组海陆过渡相干酪根生成烃类气体演化"

图2

不同压力下YC13-1-2井崖城组海陆过渡相干酪根生成甲烷碳同位素值演化"

图3

不同压力下YC13-1-2井崖城组海陆过渡相干酪根C1-5烃类气体生成的活化能分布与频率因子"

表2

不同压力下YC13-1-2井崖城组干酪根生成甲烷碳同位素动力学参数"

压力/MPa13A/12AβL/(cal/mol)βH/(cal/mol)μ/(kcal/mol)Σ/%δ13Cinit/‰
501.02256448.6864.0-27.5
1001.02157050.6867.0-27.5
1501.02246553.5016.46-27.5

图4

地质条件下(5 oC/Ma)压力对YC13-1-2井崖城组海陆过渡相干酪根生气的影响"

图5

地质条件下(5 oC/Ma)压力对YC13-1-2井崖城组海陆过渡相干酪根甲烷生成与同位素的影响"

图6

不同压力下YC13-1-2井崖城组海陆过渡相干酪根甲烷转化率与碳同位素关系"

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