渝东北地区五峰组-龙马溪组黑色页岩储层特征

Black shale reservoirs from the Wufeng and Longmaxi Formations in northeastern Chongqing

关键词:  五峰组  龙马溪组  页岩气  储层特征  渝东北

Key words:  Wufeng Formation  Longmaxi Formation  shale gas  reservoir rock  northeastern Chongqing

摘要:

以渝东北地区浅海陆棚相沉积的五峰组-龙马溪组泥页岩为研究对象,通过岩石薄片鉴定、矿物含量分析、扫描电镜、物性分析、有机地球化学分析等手段,剖析了泥页岩的岩相学、矿物学特征、储集空间类型。结果表明,五峰组-龙马溪组主要有炭质页岩、泥岩、泥质粉砂岩、硅质岩、泥灰岩和斑脱岩6种岩相类型。黑色页岩的有机质类型为Ⅰ型干酪根,有机碳含量较高,TOC普遍大于2%,最大达7.56%,平均为3.09%;有机质成熟度比较高,Ro值为1.65%~2.33%,基本上处于高成熟-过成熟阶段。矿物成分以石英矿物和黏土矿物为主,黏土矿物主要为伊利石和伊蒙间层。扫描电镜下观察,微孔隙主要包括矿物晶间孔、晶内孔、微裂缝以及有机质内微孔等。平均孔隙度为2.90%,平均渗透率为0.005×10^-3μm²。

Abstract:

The Wufeng and Longmaxi Formations in northeastern Chongqing are primarily made up of carbonaceous shales, mudstones, muddy siltstones, siliceous rocks, marls and bentonite, of which the black shales occur as the important shale gas reservoirs on a wide range of scales in the study area. The petrography, mineralogy and reservoir spaces of the black shales are treated on the basis of thin-section examination, mineral compositions, SEM, physical properties and organic geochemical signatures. These black shales are characterized by type I organic matter, higher total organic carbon(TOC)contents ranging between 2% and 7.56% with an average of 3.09%, and higher maturity levels of organic matter up to maturity to overmaturity, with Ro values ranging between 1.65% and 2.33%. The mineral compositions contain quartz and clay minerals dominated by illite and interstratified illite-montmorillonite. The porosity comprises intergranular pores, intragranular pores, micro-fissure and micropores, with an average porosity of 2.90% and an average permeability of 0.005×10^-3μm². The results of research may provide geological basis for future exploration of the shale gas in the study area.