Characterization of pore structure in Carboniferous-Permian gas shales and tight sandstones of the coal-bearing succession in the Qinshui Basin, north China

Both shales and tight sandstones have complex and heterogeneous pore systems that largely determine reservoir quality. However, there are few published data integrating the pore structure of shales and tight sandstones in coal-bearing sequences. This study presents a pore structure characterization of the Carboniferous--Permian (C3t--P1s) shales and tight sandstones of the Taiyuan-Shanxi coal-bearing succession in the Qinshui Basin of Shanxi Province, north China. Methods employed to investigate the nanoscale pore structure ( rapex) with good connectivity account for only a small fraction of the total pore volume but show significant controls on the sandstone permeability. Unlike the clay minerals and quartz in the shales, clay minerals play a negative role in sandstone porosity and permeability, whereas the quartz content contributes positively to reservoir properties due to residual primary intergranular pores. Feldspar and ankerite in the sandstones help to generate secondary dissolved pores, which greatly improve reservoir quality.