Pore types of oil shale in Jilin Province, Northeastern China

To better understand and characterize pores in oil shale systems, samples from four significant oil shale-bearing formations of the Songliao, Huadian and Luozigou basins in Jilin Province, Northeastern China, namely Qingshankou (QSK), Nenjiang (NJ), Fengtai (FT) and Longteng (LT), were prepared by breaking fresh surfaces and argon (Ar) ion polishing both perpendicular and parallel to bedding and imaged using a field emission scanning electron microscope (FE-SEM). Interparticle (interP), intraparticle (intraP) and organic matter (OM) pores are the three types of pores between or within particles of oil shale, i.e., fossils, minerals and OM. All four samples contain interP and intraP pores, but only minor OM pores occur in sample QSK. Sample FT has significant amounts of intrafossil and dissolution (intraparticle) pores due to the abundance of microfossils and the dissolution possibly caused by OM decarboxylation. Sample NJ has the highest pyrite content and contains the greatest amount of pyrite intercrystalline (intraparticle) pores, differently from sample QSK, whose amount of these pores is the lowest. Sample LT enriched with clastic particles has a large number of intercrystalline (interparticle) pores. These pores are primarily at micro-to nano-scales with various shapes, from irregular to elongated to triangular to polyhedral to rounded to elliptical, etc. There are differences in the contents of particles and OM pores between oil shales in Jilin Province and gas shales in North America. The reasons for these differences may be due to the diverse sedimentary environments and levels of maturity of oil shales. Besides, high-resolution scanning electron microscope imaging can be used to describe the diagenetic processes of oil shale.