Study on microstructure characteristics of the Niutitang formation shale and the Longmaxi formation shale

The reserves of Chinese shale gas rank the first in the world.With the increasing shortage of energy, shale gas development is getting particularly urgent.The pores and fractures in shale are not only the storage space of shale gas, but also key factors affecting the extraction of shale gas.Shale samples of the Niutitang formation and the Longmaxi formation collected from Hunan province and Sichuan province were observed through optical microscope.The characteristics of beddings, fractures and pores in the shale samples were analyzed, and the size and distribution features of pores in the samples were recorded.According to the experimental results, beddings of the Niutitang formation shale are more obvious than the Longmaxi formation shale.A few macropores along the beddings of the Niutitang formation shale were observed, while some micropores can be found along the beddings of the Longmaxi formation shale.Intergranular pores of clay minerals and the intergranular pores are the dominant pores in the Niutitang formation shale, while intergranular pores of different minerals are prevailing in the Longmaxi formation shale.Micropores dominate in samples of both formations.The frequency of pores with diameter less than 16μm and more than 100 μm in the Niutitang formation shale is higher than that in the Longmaxi formation shale.The frequency of pores with diameter between 16 μm and 100 μm in the Niutitang formation shale is lower than that in the Longmaxi formation shale.