Organic matter-hosted pore system in the Wufeng-Longmaxi (O3w-S11) shale, Jiaoshiba area, Eastern Sichuan Basin, China

The first commercial shale gas with the capability to produce 203,000 cubic meters per day were discovered in the Wufeng-Longmaxi (O(3)w-S(1)l) shale (namely, the upper Ordovician Wufeng shale (O(3)w) and the lower Silurian Longmaxi shale (S(1)l)) of well JY(1), Jiaoshiba area, Eastern Sichuan Basin, China. In this study FE-SEM, CO2 and N-2 sorption and MICP were used to characterize the pore morphology, type, size and specific surface area of the Wufeng-Longmaxi shale. We focused our research on well JY(1) to establish a standard well cross-section to allow comparison with well studied gas shales such as Barnett, Marcellus, Kimmeridge Clay and others. FE-SEM visible mineral pore sizes range from 4 nm to 3416 nm with an average of 118 nm within the Wufeng-Longmaxi shale. OM-hosted pore sizes vary from 5 nm to 1021 nm with an average of 68 nm. Within the Wufeng-Longmaxi shale, micropore volumes vary from 0.0048 cm(3)/g to 0.0078 cm(3)/g with an average of 0.0059 cm(3)/g; mesopore volumes range from 0.0108 cm(3)/g to 0.0166 cm(3)/g with an average of 0.0139 cm(3)/g; macropore volumes range from 0.00005 cm(3)/g to 0.00274 cm(3)/g with an average of 0.00108 cm(3)/g and surface areas range from 22.05 m(2)/g to 36.37 m(2)/g with an average of 27.68 m(2)/g. The average pore diameters of Wufeng-Longmaxi shales range from 5.31 nm to 7.40 nm. TOC has a significant effect on bulk shale porosity; porosity measured by FE-SEM ranges from 0.46% to 1.54%, but covers only a small fraction of the shale total porosity as the FE-SEM detection limit is in a mu m range. The majority of shale pore space (pores < 10 nm in diameter) below the FE-SEM detection are performed by CO2 and N-2 adsorption, and have an obvious relationship with the TOC. Therefore, the Wufeng-Longmaxi shale has a predominantly organic matter pore system.