Investigating microstructure of Longmaxi shale in Shizhu area,Sichuan Basin, by optical microscopy, scanning electron microscopy and micro-computed tomography

摘要

Microstructure of shale formation is the key to understanding its petrophysical and chemical properties.Optical microscopy,scanning electron microscopy and micro-computed tomography (μ-CT) have been combined for characterization of microstructure of Longmaxi (LMX)shale from Shizhu area,Sichan Basin.The results indicate that laminated LMX shale consists of mineral matrix-rich layers and organic matter (OM)-rich layers at micrometer scale in two and three dimensions.Mineral matrix layers,mainly consisting of interparticle pores and intraplatelet pores,are approximately parallel to the bedding plane.Pyrite-rich layer,mainly containing intercrystalline pores,shows a strong preferred orientation parallel to the bedding plane.OM-rich layer,mainly containing OM pores,seems to be discontinuous.In addition,intercrystalline pores are enriched in some layers,while OM pores are distributed irregularly in matrix layers.This vertical heterogeneity of pore microscopic structures in LMX shale is of great importance to understand its petrophysical and chemical properties.