川西北地区中泥盆统富孢子体烃源岩生气潜力与生烃动力学参数  

Gas generation potential and kinetic parameters of Middle Devonian sporinite-rich source rocks in the northwest Sichuan Basin

作　　者：吴子瑾 周秦 李腾飞[1,3] 纪随[1,3] 田辉 WU Zijin;ZHOU Qin;LI Tengfei;JI Sui;TIAN Hui(State Key Laboratory of Organic Geochemistry,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,Guangdong,China;University of Chinese Academy of Sciences,Beijing 100049,China;CAS Center for Excellence in Deep Earth Science,Guangzhou 510640,Guangdong,China)

机构地区：[1]中国科学院广州地球化学研究所,有机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]中国科学院深地科学卓越创新中心,广东广州510640

出　　处：《地球化学》2022年第5期516-527,共12页Geochimica

基　　金：国家杰出青年科学基金(41925014);十三五油气专项课题(2017zx05008-002-004);中石油西南油气田项目(XNY-页岩院-JS2021-49)联合资助。

摘　　要：川西北泥盆系已成为四川盆地天然气勘探开发的重要层系之一,对于该区烃源岩的关注也逐渐增多,但相关生气研究仍比较少。本研究对新发现的中泥盆统富孢子体烃源岩开展了有机岩石学和黄金管–高压釜热模拟等实验,明确了该类烃源岩的生气潜力与特征,并获取了相应的生气动力学参数和甲烷碳同位素分馏动力学参数。结果表明,中泥盆统富孢子体烃源岩中孢子体含量异常丰富,TOC含量高(5.65%~14.24%),有机质以Ⅰ-Ⅱ型干酪根为主,封闭体系下C_(1~5)总气最高产率为399.7 mL/g(每克TOC的产率,下同)。C_(1~5)总气生成的频率因子为2.84×10^(14) s^(−1),离散型活化能分布范围在213.5268~314.0100 kJ/mol之间,活化能主峰为280.5156 kJ/mol。甲烷生成的频率因子为4.72×10^(14) s^(−1),高斯型分布的活化能均值μ为280.5156 kJ/mol,方差σ为29.3076 kJ/mol,活化能分布在221.9004~339.1308 kJ/mol之间。甲烷^(13)C_(1)和^(12)C_(1)生成活化能差值(ΔE)最大为280.5156 J/mol,最小为91.8165 J/mol,生成甲烷母质的初始碳同位素为−28.1‰。地质条件下的天然气生成与甲烷碳同位素分馏模拟结果表明,该套烃源岩可能是川西北泥盆系气藏中天然气的来源之一。以上认识为研究区下一步天然气勘探提供了新思路。The Devonian has become one of the important strata for natural gas exploration in the northwest Sichuan Basin.Progressively more attention has been paid to the source rocks in this area,but there are still few relevant studies on the gas generation potential.Based on organic petrology and pyrolysis experiments,the geochemical and organic petrological signatures and the gas generation potential of the newly discovered Middle Devonian sporinite-rich source rock were investigated.The kinetic parameters of gas generation and the methane carbon isotope fractionation were also determined.The results showed that the Middle Devonian source rocks investigated here have high TOC contents of 5.65%–14.24%,with extremely abundant sporinites,and that the organic matter is dominated by type I and II kerogen.The maximum yield of C_(1–5 )is 399.7 mL/g(normalized to per gram TOC),indicating a high gas generation potential.The frequency factor of C_(1-5) gas generation was 2.84×10^(14) s^(−1),and the activation energy ranged from 213.5268 to 314.0100 kJ/mol,with a peak value of 280.5156 kJ/mol.The frequency factor of methane generation was 4.72×10^(14) s^(−1),and the mean value of the Gaussian-type activation energy distribution was 280.5156 kJ/mol,with a varianceσof 29.3076 kJ/mol,and the activation energy ranged from 221.9004 to 339.1308 kJ/mol.The maximum value of the activation energy difference(ΔE)between ^(13)C_(1) and ^(12)C_(1) generation was 280.5156 J/mol,and the minimum value was 91.8165 J/mol,and the initial carbon isotope value of the methane parent material was−28.1‰.The geological model of gas generation and methane carbon isotopic fractionation suggests that the gas generated from the sporinite-rich source rock in the Middle Devonian is likely an important source of the Devonian natural gas discovered in the northwest Sichuan Basin,which provides new insight for further gas exploration.

关 键 词：烃源岩 孢子体 热模拟实验 生气动力学 四川盆地 

分 类 号：P593[天文地球—地球化学]