四川盆地南部五峰组—龙马溪组页岩地质甜点层特征——以威远—荣昌区块为例

Characteristics of Wufeng-Longmaxi Formations shale sweet layer:Case study of Weiyuan-Rongchang block of SINOPEC

以四川盆地南部威远-荣昌页岩气区块五峰组-龙马溪组典型取心井为例,基于岩心观察描述,利用薄片鉴定、氩离子抛光-扫描电镜、物性测试、X-射线衍射及地球化学分析、现场含气量解析等多种测试手段,从岩石学矿物组成、有机地球化学特征、成烃生物类型及组合、储集物性、孔隙类型和结构及含气性等方面,系统评价了五峰组-龙马溪组页岩地质甜点层段特征。研究表明,威远-荣昌地区地质甜点层岩性主要以黑色炭质页岩为主,纹层发育,碳酸盐矿物含量明显高于焦石坝地区,硅质含量相对较低;有机碳含量高,演化处于高过成熟阶段,生气充足,富含笔石、藻类、海绵骨针、细菌等成烃生物化石;甜点层无机孔和有机孔发育较好,无机孔隙主要以黏土矿物孔、长石蚀变孔、黄铁矿晶间孔为主,为页岩气提供赋存空间。目的层具有较有利的顶底板条件,不存在较大破坏性断裂和破坏性的流体活动,保存条件好,使得页岩气富集并得以保存。最终体现在含气性方面,具有高原地含气量和高初始逸散速度的特征,为高产稳产提供了可能。

Taking the typical core well of the Wufeng-Longmaxi formations in the Weiyuan-Rongchang shale gas block of the South Sichuan Basin as an example and based on the core observation,this study sys tematically evaluated the Wufeng-Longmaxi geological sweet section from petrology,mineral composition,organic geochemistry,hydrocarbon generation type and combination,physical property characteristics,pore type and gas content by using thin slices,argon ion polishing-scanning electron microscopy,physical prop erty test,X-ray diffraction and geochemical analysis,on-site gas testing methods such as gas content analy sis.The research shows that the lithology of geological sweet layer in Weiyuan-Rongchang area is mainly black carbonaceous shale and the stratum is developed.The carbonate mineral content of studied area is sig nificantly higher than that in the Jiaoshiba area,the quartz mineral content is relatively low and the organic carbon content is high.The evolution is at a stage higher than the mature stage and it generates large a-mount of hydrocarbons.lt is rich in hydrocarbons such as graptolite,algae,sponge needles,and bacteria.The sweet layer well developed inorganic and organic pores.The inorganic pores are mainly composed of clay mineral pores,feldspar alterations and pyrite inter crystalline pores.These holes provide space for shale gas.In addition there is no large destructive fracture and destructive fluid activity,and the storage conditions are good.Therefore,the shale gas is enriched and preserved.Finally,it is reflected in the gas content,with the characteristics of high gas content and high initial dissipation rate,which provides a possibility for high yield and stable production.