塔西南坳陷侏罗系泥页岩特征及页岩气潜力分析

Characteristics of Jurassic shales and potential of shale gas in Southwest Depression of Tarim Basin

  • 摘要: 基于塔西南坳陷侏罗系泥页岩野外露头、钻井等资料,通过岩石热解、X-衍射、扫描电镜及等温吸附等实验测试分析,对塔西南坳陷侏罗系泥页岩地质及地化特征、矿物组成、孔隙结构、吸附性能进行系统研究。研究表明研究区由于侏罗系沉积环境的连续变化,泥页岩累计厚度在60~300 m,沉积厚度大并存在NW-SE向的3个沉积中心;泥页岩具有较高的有机质丰度,平均值达到2.09%,有机质类型以Ⅲ型气型干酪根为主;岩石热解峰温Tmax(400~590℃)和镜质体反射率RO(1.4%~2.4%)表明泥页岩处在过成熟阶段并在干气窗内;研究区侏罗系泥页岩矿物组成以黏土矿物为主,石英含量次之,黏土矿物以伊/蒙混层为主,有利于页岩吸附气的富集,页岩吸附含量达0.8~1.6 m3/t,具有较强的气体吸附能力;纳米级-微米级的多种孔隙类型及微裂缝发育,可为页岩气的赋存提供空间;对比国内外典型海相、陆相页岩发现,塔西南坳陷侏罗系泥页岩主要关键指标与典型陆相页岩及海陆过渡相Lewis页岩相似甚至更好,综合分析可以初步认为塔西南坳陷侏罗系泥页岩具有较好的页岩气勘探前景。

     

    Abstract: Based on outcrops, drilling data, combining with the analysis of Rock-Eval pyrolysis, X-ray diffraction, SEM and isothermal adsorption measurement, the current study was designed to characterize geological and geochemical properties, mineral composition, pore structure as well as gas adsorption capacity.The results show that the thickness of Jurassic shales is large in this research area, about 60-300 m, because of continuous changes in sedimentary environment, it has three small depositional centers with NW-SE strike on the plane; the abundance of organic matters is high, its average value reaches up to 2.09%, the organic material primarily consists of type Ⅲ terrestrial kerogen (gas-prone); the temperature of maximum pyrolysis outputTmax (400-590 ℃) and vitrinite reflectance Ro (1.4%-2.4%) indicate that the shale is in the post-mature stage and in the gas window of hydrocarbon generation; clay minerals dominates the mineralogy followed by quartz minerals, and clay minerals are dominated by illite-montmorillonite mixed-layer, which contributes to the accumulation of adsorption gas, meanwhile, the isothermal adsorption test shows that the adsorbed gas is 0.8-1.6 m3/t, which proves that the shale has a strong ability of gas adsorption; the various types of pores and fractures in nanometer-micrometer level provide space for shale gas; in contrast to the typical marine and continental shales, the main assessment indicators of the shale in the research area is similar to (even better than) typical continental shales and marine-continental transitional Lewis shale in the San Juan basin.A comprehensive analysis indicates that Jurassic shales in Southwest Depression of the Tarim Basin could tentatively be regarded as a potential shale gas exploration target.

     

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