Pore types and characteristics of shale gas reservoir: A case study of Lower Paleozoic shale in Southeast Chongqing

Through thin section analysis,scanning electron microscopy and argon-ion milled surfaces technique,the pore types and characteristics of Lower Paleozoic gas shales in Southeast Chongqing were observed and described.Based on the experimental methods of total organic carbon content,XRD analysis,rock porosity,nitrogen adsorption and methane isothermal adsorption,the pores' contribution to gas storage was analyzed and their impacts on hydrocarbon migration was discussed.The results showed that the organic pore,intraparticle pore,interparticle pore and microfracture are four pore types developed in Lower Paleozoic shale gas reservoir.Most dispersed pores on the organic matter are nanoscale pores,intraparticle or interparticle pores with granular quartz appeared;pore space spreads between small crystals inside pyrite;flake structures produce pores by flocculation of clay;microfractures occur within the matrix of shale,some are millimeter sized.Different types of pores could provide various sized storage space and there is an obvious linear correlation between gas adsorption capacity and pore characteristic parameters(TOC,BET surface area,BJH total pore volume).Microfractures and interparticle pores are most likely to contribute to hydrocarbon migration.