四川盆地焦石坝地区五峰-龙马溪组页岩元素地球化学特征及对页岩气开发的意义

第40卷第1期 2018年1月

石油实验地质

P E T R O L E U M G E O L O G Y&E X P E R I M E N T

V〇1.40,N〇.1

Jan. ,2018

文章编号：100卜6112(2018)0卜0078-12doi：10.1178L/sysydz201801078四川盆地焦石坝地区五峰|龙马溪组页岩

元素地球化学特征及对页岩气开发的意义

甘玉青，王超，方栋梁，杨兰芳，周新科，张萍

(中国石化江汉油田分公司勘探开发研究院，武汉430223)

摘要:选择四川盆地焦石坝地区JYAJYD两口井的85块页岩岩心样品，进行了有机碳和主、微量元素测试分析。通过分析主、微 量元素在剖面上的纵向变化特征，对焦石坝地区五峰组一龙马溪组含气页岩的氧化还原条件和古生产力状况进行了研究,讨论了

五峰组一龙马溪组有机质富集的主控因素;探讨了地球化学元素对页岩可压性的影响和含气性的指示。研究区五峰组一龙马溪组下部优质气层段有机质含量高，平均值为3.07%。与含气页岩段相比,优质气层段页岩中的SiO:和CaO含量较高,Mo、&、V、Ni、Th 和L等氧化还原敏感元素富集。V/0、V/Sc、L/Th和Ni/Co等氧化还原条件判别指标表明，五峰组沉积期以缺氧一贫氧环境为主，龙马溪组沉积期下部以缺氧环境为主，往上则主要为含氧环境。古生产力指标Ba(、s)指示五峰组一龙马溪组页岩沉积期具有高等生产力背景。优质气层段有机碳含量与Mo/A1、L/Th、N^Co、V/〜值之间存在明显的正相关,说明有机质富集主要受氧化还原条件控制。另外，优质气层段页岩生物成因的硅质含量高，且有机碳含量与Si〇2含量呈正相关,有利于形成天然裂缝和后期人工压裂改造。优质气层段的地化元素比值明显高于含气页岩段，说明化学元素比值与页岩含气性之间存在一定的相关性。

关键词：主、微量元素；有机质富集;可压性;含气性;页岩;五峰组一龙马溪组;焦石坝地区

中图分类号:TE122.113 文献标识码:A

Element geochemical characteristics of the Wufeng-Longmaxi shale in Jiaoshiba area，Sichuan Basin and their significance to shale gas development

G A N Yuqing，W A N G Cha o,F A N G Dongliang，Y A N G Lanlang，Z H O U Xinke，Z H A N G Ping (Research Institute of Petroleum, Exploration and Development，SINOPEC Jianghan, Oilfield Company，Wuhan，Hubei 430223，China) Abstract：A t o t a l ol85 shale core samples from wells J Y A and J Y D in Jiaoshiba area o l Sichuan Basin were selected to t e s t their organic carbon contents，major and trace elements.The redox conditions and paleoproductivity o l the gas­bearing shale in the Wufeng-Longmaxi formations in the Jiaoshiba area were studied by analyzing the vertical variation characteristics o l the major and trace elements in the profile.Meanwhile，the controls for organic matter enrichment in the Wufeng-Longmaxi formations were explored.Moreover，the impact o l geochemical elements on shale compressibi­l i t y and gas-bearing property were studied.The organic carbon content in the high gas-bearing interval lrom the Wuteng Formation to the lower part o l Longmaxi Formation i s high with an average value o l 3.07%. Compared with the common gas-bearing shale，Si〇2and CaO contents are higher in the high gas-bearing shale，and redox-sensitive elements such as M o，Cr，V，Ni，Th and U are enriched.The redox condition indicators such as V/Cr，V/Sc，U/Th and Ni/Co indicated that the Wuleng Formation was mostly deposited in suboxic to anoxic conditions，whereas the anoxic environment dominated during the early sedimentary stage ol L^)ngmaxi shale and evolved into aerobic condi­tions later on.The contents o l biological productivity-related element Ba(^s)reflected a high paleoproductivity，whereas T O C content has an obvious positive correlation with redox proxies (M o/Al，U/T h，Ni/Co and V/Sc)in the high gas-bearing interval，suggesting that the enrichment ol organic matter was predominantly controlled by redox environ­ment.In addition，the biogenic siliceous content o l high-quality gas-bearing shale i s high，and the organic carbon con­tent i s positively correlated with the Si〇2content，which i s conducive to the lormation o l natural lractures and the later a r t i l i c i a l lracturing.The ratio o l geochemical elements in the high gas-bearing interval i s signilicantly higher than that

ol common interval，indicating that there i s a certain correlation between chemical element ratios and shale gas. Key words：major and trace elements；organic matter enrichment;compressibility;gas-bearing；shale;Wuleng-

Longmaxi formations;Jiaoshiba area

收稿日期：2017-10-13;修订日期：2017-12-27。

作者简介:甘玉青（1981 —），女，硕士，工程师,从事油气藏地质评价工作。E-mail:iamagaii@

基金项目：国家科技重大专项（2016ZX05060)和中国石化科技项目（P17014-3)资助。