Micro-pore structure and connectivity of the Silurian Longmaxi shales, southeastern Sichuan area

Micro-pore structure and connectivity of the Silurian Longmaxi shales in the southeastern Sichuan Basin were studied using CT, FIB-SEM, Ar⁺-SEM, and TEM techniques. Four modes for micro-pores in shales were determined to be as follows. (1) Intergranular micro-pores which exist between mineral grains and account for a small proportion of the total. (2) Intragranular micro-pores which mainly exist in intergranular dispersed organic matter or symbiosis organic matter with globular pyrite, and some between clay layers. (3) Grain boundary fractures which exist around organic or mineral grains, and work as a connective network for the shales. (4) Interlayer bedding which provides filtration channels. Intraparticle organic nano-pores are bubble like, show a normal size distribution, and are connected to each other. Their diameter mainly ranges from 30-90 nm and throat width ranges from 7-20 nm. Interlayer bedding accounts for 1%-2% of total shale pores and fractures, and are favorable filtration channels. Micro-pores and fractures in organic matter provide the main reservoir space for shale gas, grain boundary fractures form a connective network, while interlayer bedding provides filtration channels.