摘要
有机孔普遍欠发育是我国南方寒武系页岩气勘探中遇到的实际地质问题,然而,造成有机孔欠发育的主控因素及演化机制迄今为止仍然存在很大争议。该文综合整理了笔者团队近年来对中上扬子不同地区寒武系页岩储层的研究进展,进一步讨论了下寒武统页岩孔隙发育特征与总有机碳含量(TOC)和成熟度的关系,以及排烃作用对下寒武统富有机质页岩孔隙发育的影响。研究表明,中上扬子地区下寒武统富有机质页岩的TOC含量、矿物组成和岩相特征在横向和纵向上波动较大,有机孔发育特征也表现出很强的非均质性。整体上,下寒武统富有机质页岩孔隙度随TOC含量的增加呈先增大后减小趋势,但在不同地区存在较大差异。另一方面,尽管研究区下寒武统页岩已经普遍进入过成熟阶段,但相比之下,位于过成熟早-中期(Eq R_(o)=2.0%~3.0%)的鄂西宜昌地区和陕南汉中地区下寒武统页岩有机孔发育情况相对优于过成熟晚期(Eq R_(o)=3.0%~3.5%)的四川威远地区,而成熟度最高(Eq R_(o)>4.0%)的黔北地区有机孔发育情况则最差。此外,页岩孔隙发育特征与矿物组成、TOC含量在鄂西宜昌地区ZK003井、EYY1井和贵州开阳ZK909钻孔等研究剖面上均表现出明显二分段性,其中,富有机质页岩二段(上段)具有中等TOC含量和富黏土矿物的典型特征,其发育有机孔情况优于高TOC含量的富有机质页岩一段(下段),与黏土矿物伴生的有机质孔隙十分发育。因此,除了高TOC含量页岩容易被压实和过高成熟有机质发生碳化使得有机孔塌陷和被充填这两种可能的影响机制外,近年来笔者团队还重点提出了排烃对寒武系页岩孔隙发育的影响,特别是下寒武统富有机质页岩一、二段在生油窗的排烃效率差异,不仅解释了其孔隙发育差异的原因,而且研究结果也为寒武系页岩优质储层筛选及页岩气勘探的“甜点段”预测提供了重要参考。
Poor organic pore development is a practical geological problem in the exploration of Cambrian shale gas in south China,however,the key factors on the underdevelopment of organic pores and associated evolutionary mechanism are still controversial so far.This paper summarizes the research progress of the author′s team on Cambrian shale reservoirs in different areas of the Middle and Upper Yangtze in recent years,and further discusses the relationship between pore development characteristic,total organic carbon content(TOC),and maturity of the Lower Cambrian shale,as well as the effect of hydrocarbon expulsion on pore development in Lower Cambrian organic-rich shale.The research shows that the TOC content,mineral composition,and lithofacies of the Lower Cambrian organic-rich shale in the Middle-Upper Yangtze region fluctuate greatly horizontally and vertically,and the organic pore development also shows strong heterogeneity.Generally,the porosity of the Lower Cambrian organic-rich shale increases first and then decreases with the increase of TOC content,but there are great differences in different regions.On the other hand,although the Lower Cambrian shales in the study area have generally entered the over-mature stage,the development of organic pores in the Lower Cambrian shale in the Yichang region of western Hubei and the Hanzhong region of southern Shaanxi during the early-middle stage of over-maturity(Eq R_(o)=2.0%~3.0%)is relatively better than that in the Weiyuan area of Sichuan,which is in the late stage of over-maturity(Eq R_(o)=3.0%~3.5%),while the development of organic pores in the northern Guizhou area with the highest maturity(Eq R_(o)>4.0%)is the worst.Furthermore,the shale is generally characterized by two segments in pore characteristics,mineral composition and TOC content on the profiles from the wells ZK003 and EYY1 in the Yichang area(Hubei Province)and the well ZK909 in the Kaiyang area(Guizhou Province).The second organic-rich interval(upper member)with medium TOC content and high clay content has more organic pores than the high TOC content but relatively clay-poor interval,and the organic pores are mainly developed in OM-clay mineral complexes.Therefore,in addition to the two possible mechanisms,such as being easily compacted for the organic-rich shale with high TOC content and the collapse and filling of organic pores due to the carbonization of over-mature OM,we also proposed that hydrocarbon expulsion has an effect on the development of pores in the Cambrian shale.In particular,the difference in hydrocarbon expulsion efficiency between the two intervals of the Lower Cambrian organic-rich shale during oil window not only partly explains the reasons for the heteroegenity in pore development,but also the results are helpful for the selection of high-quality Cambrian shale reservoir and prediction of the dessert interval in shale gas exploration.
作者
邵德勇
张瑜
宋辉
孟康
罗欢
李艳芳
吴陈君
唐玄
张同伟
SHAO Deyong;ZHANG Yu;SONG Hui;MENG Kang;LUO Huan;LI Yanfang;WU Chenjun;TANG Xuan;ZHANG Tongwei(State Key Laboratory of Continental Dynamics,Department of Geology,Northwest University,Xi′an 710069,China;School of Earth Sciences,Lanzhou University,Lanzhou 730000,China;State Key Laboratory of Organic Geochemistry,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,China;College of Resources and Environment,Yangtze University,Wuhan 430100,China;School of Energy and Resource,China University of Geosciences(Beijing),Beijing 100083,China;Bureau of Economic Geology,Jackson School of Geosciences,The University of Texas at Austin,Austin,TX 78713,USA)
出处
《西北大学学报（自然科学版）》
CAS
CSCD
北大核心
2022年第6期997-1012,共16页
Journal of Northwest University（Natural Science Edition）
基金
国家自然科学基金(41730421,42102189)
陕西省自然科学基础研究计划青年项目(2021JQ-450)。
关键词
页岩气
中上扬子
下寒武统
有机孔
排烃效率
shale gas
Middle-Upper Yangtze
Lower Cambrian
organic pore
hydrocarbon expulsion efficiency
