Evaluation of shale reservoir and its influencing factors in coal-bearing strata of Qinshui Basin

Based on the coring samples of shales in the center and south of Qinshui Basin, this study focuses on Taiyuan formation in Carboniferous system and Shanxi formation in Permian system which are the main gas production layers and analyses on the aspects including source rocks, petrology characteristics, reservoir property and its influence factors.The research shows that the shale samples has good hydrocarbon generating potential and the high content of TOC is found in the areas with thick shale.As one of the organic matter maturity indexes, R_o is between 1.33%-2.17%, which reaches the threshold of gas generation.The organic matter types are all type I kerogen.Whole rock analysis shows that shale samples has a high content of brittle minerals, and most of the content of which is more than 40%.The illite/smectite mixed layers and kaolinite contains the highest content of clay minerals, next is chlorite and illite.According to the scanning electron microscope, shale develops mineral dissolution pores, intergranular pore, and microfractures.The porosity is between 0.7%-3.8%, which is little lower than that in North American shale, and the permeability is between 0.002 8×10^-15-0.127 3×10^-15 m², which has no much difference with that of North American shale.It is the kaolinite and illite in the clay minerals which have great influence on reservoir physical properties.The kaolinite plays a constructive role in the development of porosity and permeability.While the higher content of illite is, the worse the effect on reservoir is.The parameters of organic geochemistry show that the shale in Qinshui Basin has high hydrocarbon potential.The porosity and permeability of the reservoir is well and the high content brittle minerals in it are favorable to the shale reservoir fracturing treatment.