摘要
湖北宜昌地区埃迪卡拉纪—寒武纪界线附近地层格架显示宜昌地区埃迪卡拉纪晚期—早寒武世时期的构造古地理格局具有隆、凹相间的特点。凹陷区是寒武系水井沱组下段富有机质页岩发育的有利区带。凹陷区内水井沱组下段页岩微量元素V/Cr、Ni/Co、V/(V+Ni)的比值和化学蚀变指数(CIA)指示水井沱组下段页岩总体上形成于缺氧或硫化环境,但自下而上氧化还原条件有逐步改善的趋势。与氧化还原环境变化对应,出现了总有机碳(TOC)和生源钼(Moxs)的同步减小,证明TOC受氧化还原环境和海底有机碳通量的双重影响。TOC与Moxs的相关性明显高于TOC与生源镍(Nixs)的相关性,据此,并结合同期地层有机碳同位素组成特征,推测寒武纪早期海底可能发生了天然气水合物的溶解和甲烷释放。宜昌地区寒武系水井沱组页岩TOC与页岩的含气量、石英和黄铁矿等脆性矿物含量的高度相关性证明TOC是页岩气储层品质评价的最重要参数之一,具有相对较高TOC含量的水井沱组下段中—下部无疑是水井沱组页岩气的最优质储层。宜昌地区海相地层埋藏演化史研究,揭示宜昌地区下寒武统储层中的有机质在晚三叠世中期进入生气高峰之后,再未发生二次生烃,黄陵隆起及其演化有效防止了有机质的过度热演化和页岩气储层的破坏。寒武系水井沱组页岩气富集受控于总有机碳含量和黄陵隆起及其演化。
According to the stratigraphic framework across late Ediacaran-Early Cambrian boundary in Yichang, western Hubei, there existed uplifts alternating with sags during the Precambrian-Cambrian transition. The sags were favorable for the deposition of the rich organic shale of the Lower member of Cambrian Shuijingtuo Formation. V/Cr, Ni/Co, V/（V＋Ni） and chemical indexes of alteration （CIA） indicate that these shales were formed in an anoxic or euxinic environment. However, a relatively oxic water and a synchronous decrease in total organic carbon （TOC） and biogenic Mo （Moxs） were found in the Lower Member Shuijingtuo Formation, which demonstrates that TOC was affected by both redox environment and marine organic carbon flux. The correlation between TOC and Moxs is much better than that of the TOC and biogenic Ni （Nixs）. This phenomenon, together with the composition of the δ13Ccarb and δ13Corg in the same interval strata, indicates that there might exist dissociation of gas hydrate or release of methane. The high correlation between TOC and shale gas content and brittle minerals, （e.g. quartz, pyrite and some other minerals） indicates that TOC is one of the most importaut factors for evaluating the quality of shale gas reservoirs. Thus the lowermiddle part of the Lower member of Shuijingtuo Formation characterized by high TOC should be the best reservoir of the shale gas in the Shuijingtuo Formation. The study of burial and evolution history of the marine sedimentary in Yichang area indicates that the source rock of the Lower Cambrian had not gone through secondary＇ hydrocarbon generation after reaching its gas generation peak in middle Late Triassic because of the restriction from the Huangling uplift, and thus avoided the excessive thermal evolution of the organic matter and the destruction of the shale gas reservoirs. Enrichment of the shale gas in the Cambrian Shuijingtuo Formation in Yichang was controlled by TOC, Huangling uplift and its evolution.
作者
陈孝红
危凯
张保民
李培军
李海
刘安
罗胜元
CHEN Xiaohong;WEI Kai;ZHANG Baoming;LI Peijun;LI Hai;LIU An;LUO Shengyuan(Wuhan Center of China Geological Survey, Wuhan 430223, Hubei, Chin)
出处
《中国地质》
CAS
CSCD
北大核心
2018年第2期207-226,共20页
Geology in China
基金
中国地质调查局项目(DD20179615)
国家重大科技专项(2016ZX05034-001-2)联合资助~~
关键词
页岩气
地质条件
富集模式
黄陵隆起
水井沱组
寒武纪
宜昌
shale gas
geological control
enrichment mode
Huangling uplift
Shuijingtuo Formation, Cambrian, Yichang
