Relationship between mineral composition and micro-pores of Niutitang-Formation shale in Micangshan-Hannan Uplift

Based on the shale samples from Niutitang Formation in Micangshan-Hannan Uplift, some technical experimental devices, such as X-ray diffraction (XRD), low-temperature nitrogen gas adsorption and argon ion figuring-field emission scanning electron microscope (Ar-FESEM) were used to analyze the relationship between mineral composition and micropore structure of Niutitang-Formation shale.The results show that the mineral composition of Niutitang-Formation shale in Micangshan-Hannan Uplift is complex.The mineral composition are mainly quartz and clay minerals, then feldspar, carbonate minerals and pyrite, and the average content of quartz and clay minerals are 41. 35% and 31. 55% respectively.The brittleness index (BI) of Niutitang-Formation shale distributes mainly in the range from 0.6 to 0.8 that demonstrate a good compressibility and brittleness. Some nano-sized fractures are along the edge of particles, and few intergranular pores and dissolved pores are formed by quartz and feldspar. There are lots of beddingcracks, pores among clay particles and cracks between schistose minerals formed in clay minerals.Multiple types of micropores are developed in organic matter, such as pores by hydrocarbon expulsion, fractures between organic matter and other minerals and mold pores. The BET and micropore volume have the positive correlation with the content of clay minerals and organic matter, but not with the quartz and feldspar.And the TOC has a positive correlation with BET but not with micropore volume.Also, the results show that the clay minerals are the main influences on the development of macropores, mesoporous and micropores of Niutitang-Formation shale. However, TOC is the main carrier of micropore which means the macropores and mesoporous are not well-developed in organic matter.The pyrite inhibits the growth of micropore after promoting it due to its own unique pore space structure and interaction with organic matter, and the functional mechanism changes when the content of pyrite increases up to 2.8%.