渝东南龙马溪组下部页岩岩石学特征与优质储层形成机理

摘要

Shale samples from lower Longmaxi Formation in Qijiang,Sanquan,Shizhu and Fuling in South-east Chongqing were selected for the study.Based on the analysis of the X-ray diffraction,TOC,brittleness test,high pressure mercury injection and low temperature nitrogen adsorption,the petrographic characteristics including mineral composition,organic characteristics,pore characteristics and brittleness of shale reservoir were studied.The perspect of reservoir petrology was evaluated and the influences of petrological characteristics on the formation mechaism of high-quality reservoirs were discussed.The results showed that mineral compositions of Longmaxi Formation shale reservoir can be divided into brittle minerals of quartz and clay minerals of illite.The content of brittle minerals at the bottom was significantly higher.The average value of TOC content is above 2% and the organic matter is over mature.The type of pores are complex and various types of pore were identified including organic nano pores,flake pores in clay mineral,dissolution pores in matrix mineral,and intergranular pores in framboidal pyrite.The main specific surface area and reservoir space were contributed by the nanoscale pores and the morpholohy characteristics of pores are sophisticated with various shapes such as parallel-plate size etc.The mechanics brittleness is good and the brittleness index is favorable for microfractures in reservoir and artificial fracturing.The lower Longmaxi Formation reservoir is high quality reservoir with special petrological characteristics which is formed in deep shelf and has experienced the late diagenesis stage,and therefore have suitable mineral compositions with developed nanopores,microfractures and good mechanics brittleness.Shale reservoir material compositions are the basis for the formation of high quality reservoir.The study is significance to explore the formation mechanism of physical characteristics and its control factors from the angle of the petrological characteristics in reservoir research.%以渝东南綦江、南川、石柱及涪陵的龙马溪组下部页岩为例,通过X射线衍射、氩离子抛光-场发射扫描电镜、TOC、脆性力学、高压压汞实验、低温氮吸附实验等测试手段,综合探明页岩储层矿物组分、有机质特征、孔隙特征、力学脆性等岩石学特征,对储层进行岩石学角度的评价,并讨论岩石学特征对优质储层形成的影响.结果显示:龙马溪组下部页岩储层岩石矿物组分可以分为以石英为主的脆性矿物和以伊利石为主的黏土矿物,底部脆性矿物含量更高;TOC平均值高于2%,达到过成熟阶段;孔隙类型复杂,识别出有机质纳米孔、黏土矿物片状孔、骨架矿物溶蚀孔等多种形貌-成因孔隙,纳米孔提供了主要的比表面积和储集空间;孔隙形貌复杂,发育平行板状等多种形态类型;岩石力学脆性较好,有利于微裂隙发育与压裂造缝.研究区龙马溪组下部页岩形成于深海陆棚相,经历了晚成岩作用阶段,矿物组分适宜,纳米孔、微裂隙发育,具有较好的力学脆性,是具有特殊岩石学特征的优质页岩气储层.页岩储层的岩石物质组成特征是优质储层形成的基础,从岩石学特征的角度对储层展开研究,对探究页岩储层的物性成因及其受控因素具有重要意义.