Classification and characterization of gas shale pore system

There is not a unified pore classification for the unconventional gas shale reservoir so far. Furthermore, the application of tools and techniques used to characterize conventional reservoir rocks commonly provides erroneous results for shale reservoirs. On the basis of the investigation of the recent classification of gas shale pore system, a comprehensive classification integrating pore occurrence with pore structure has been suggested in this paper. According to the pore occurrence, the pore in the gas shale reservoir can be divided into two categories. The one is not controlled by individual matrix particles, which is the fracture pore, and the other is the matrix-related one, which can be further classified into three major matrix-related pore types in which two pore types are associated with the mineral matrix and the third one is associated with organic matter (OM). Pores associated with mineral particles can be subdivided into interparticle pores that are found between particles and crystals and intraparticle pores that are located within particles. Organic-matter pores are intraparticle pores located within OM. Young shallow-buried muds contain only interparticle and intraparticle pores that are greatly diminished during burial and compaction. With deeper burial, OM pores develop during hydrocarbon thermal maturation, and intraparticle dissolution pores may develop by acidic fluid generated during decarboxylation of kerogen. The comprehensive classification in this paper combined the occurrence factor of pores with the texture one from the IUPAC's micropore, mesopore and macropore. Some modern characterizing methods for gas shale pores have been introduced. These methods include visual imagination of pores with such as TEM and FIB-SEM, and quantitative measurements with such as mercury porosimetry, low-pressure gas adsorption analyses and NMR.