鄂西宜昌地区寒武系页岩测井评价及优质储层识别

E-Log Evaluation of the Cambrian Shale Play and Identification of Favorable Reservoir in the Yichang Area,Western Hubei Province

中扬子地区下寒武统是我国页岩气勘探开发的热点层系,页岩测井是评价页岩气储层的重要手段。宜昌地区寒武系处于浅水陆棚相带,页岩中碳酸盐岩组分含量高,大量发育灰质条带和灰岩透镜体,岩性非均质性强,识别优质储层是页岩气评价的基础。本文利用常规测井、特殊测井以及岩心样品分析化验资料,综合分析了宜页1井寒武系水井沱组页岩岩性密度、自然伽马、电阻率、声波时差、补偿中子、核磁共振以及岩性扫描测井特征,获得了富有机质页岩测井的识别方法。研究显示:(1)宜页1井中水井沱组富有机质页岩厚度为68.3 m,具有“五高两低”的地球物理响应特征,水井沱组页岩自上而下,密度测井可划分为指状波动段、中部稳定段、下部低密度段“三段式”特征,电阻率测井可划分为尖峰状高电阻灰质泥岩段、电阻率千欧段,低电阻率含气页岩段;(2)富有机质页岩的密度与TOC呈较好的负相关性,随着深度增加、TOC含量增大,声波时差、补偿中子逐渐增大,元素测井上Si、S含量增加,Ca含量降低;(3)利用孔隙度曲线和U、Th/U等反映TOC的曲线叠合,以及U与RD、DEN、中子、AC的交汇图,可有效区分出优质页岩(TOC>2.0%)、贫有机质页岩和灰质页岩。

The Lower Cambrian shale in the Middle Yangtze region is a hot spot for shale gas exploration and development in China.The Cambrian Series in the Yichang area,western Hubei province is in the shallow shelf phase zone,with high content of carbonate components in shale,and a large number of ash streaks and ash lenses well developed.Strong non-homogeneous of lithologies means that identification of high-quality reservoirs is fundamental for shale gas evaluation.The litho-density,natural gamma,resistivity,interval transit time,compensated neutron,nuclear magnetic resonance and lithology scanning logging characteristics of the early Cambrian Shuijingtuo shale in Yiye 1 well were comprehensively analyzed using conventional logging,special logging and core sample analysis.The logging identification methods of organic-rich shale were analyzed.The study shows that:(1) the thickness of the organic-rich shale of the Shuijingtuo Formation is68.3 m,with the geophysical response characteristics of "five highs and two lows".From top to bottom,the density logging can be divided into three sections:finger-like fluctuation section in the upper part,stable section in middle part,and low density section in the lower part.The resistivity logging can also be divided into spiky high resistance of calcareous shale section,resistivity kilo-ohm section,and low resistance of gas-bearing shale section.(2) The density of organic-rich shale has a good negative correlation with TOC content.With the increase of depth,the TOC content,the interval transit time and compensated neutron gradually increase,as well as the Si and S content increases,and Ca content decreases on elemental logs.(3) Using the overlay of porosity logging curves and curves reflecting TOC such as uranium and thorium/uranium,as well as intersection diagram between U and RD,DEN,neutron,AC,the high quality shale(TOC>2.0%),poor organic matter shale and calcareous shale can be separated effectively.