中国南方早古生代页岩有机质的扫描电镜研究

SEM observation of organic matters in the Eopaleozoic shale in South China

南方早古生代页岩是我国页岩气勘探开发的首选层系,其有机质的研究极其必要和重要。通过制取页岩样品的自然断面(垂直层理的面和平行层理的面)和氩离子抛光面,在场发射扫描电镜下,对安徽省、贵州省、四川省等地早古生代(下寒武统、上奥陶统、下志留统)页岩有机质的显微组分、化学成分、赋存状态、孔隙类型等进行了较系统的观测和研究。结果表明,早古生代页岩的有机显微组分以生烃能力强的沥青质体和菌藻体为主。沥青质体由几至几十纳米的球粒组成,无固定形态,赋存状态有条带状、填隙状、薄膜状。菌藻体具有明显的生物形貌特征,形状各种各样,大小为几十微米,赋存状态主要为碎屑状。在显微组分识别的基础上,将有机质孔隙的成因类型划分为生物孔、气孔、沥青球粒孔和铸模孔。其中气孔和沥青球粒孔均发育于沥青质体内部,孔径主要为纳米级,是有机质生烃演化的直接见证,其发育程度可作为烃源岩生烃潜力的评价指标之一。

The Eopaleozoic shale in South China is assessed as the preferred target for shale gas exploration and develop-ment in China,and the research on its organic matters is imperative.Some shale samples are taken from the Eopaleozoic such as the Lower Cambrian,Upper Ordovician and Lower Silurian in Anhui,Guizhou and Sichuan provinces in South China.The naturally fractured surfaces（ perpendicular to or parallel to the beddings） and the argon ion milled surface are prepared from these shale samples.Under the scanning electron microscope（SEM）with field emission,the maceral,che-mical composition,occurrences of the organic matters and pore types are systematically observed and studied.The results show that the organic maceral types are dominated by bituminite and bacteria and algae body with strong potential of hy-drocarbon generation.The bituminite is composed of spherulites with several to dozens of nanometers in diameter with stripped,interstitial,thin films and amorphous occurrences.The bacteria and algae body has obvious characteristics of bio-logical morphology,mainly in clastic form and dozens of micrometers in diameter.On the basis of identification of maceral, the genetic types of the organic pores are classified into biological pore, vesicular pore,bitum-spherulite pore and molded pore.And both the vesicular pore and bitum-spherulite pore occur in the interior of bituminite and their diameters are of nanometer-scale,which are the direct evidences of hydrocarbon generation from organic matters.Therefore,the development degree of these pores is viewed as one of the indexes for hydrocarbon generation potential assessment of the source rocks.