Pore structure characteristics and evolution laws of coal-measure shale in the Shanxi Formation,eastern the Ordos Basin

QIAO Yu; SONG Dangyu; LIU Weiqing; YU Zhen

doi:10.16186/j.cnki.1673-9787.2022030039

Abstract：Objectives In order to clarify the development and evolution laws of pores structure in coal-measure shale,Methods this study used X-ray diffraction,rock pyrolysis,scanning electron microscope,low-pressure CO2/N2 gas adsorption and high-pressure mercury intrusion experiments to characterize the pore structure of various lithofacies in Shanxi Formation coal-measure shale in the eastern Ordos Basin.Results The research shows that the Shanxi Formation mainly develops silica-rich argillaceous shale lithofacies(A-1),siliceous/argillaceous mixed shale lithofacies(M-2),and clay-rich siliceous shale lithofacies(S-3).Meso-pores are the main origin of pore volume,with a contribution of more than 65%,while micropores are the main origin of reservoir specific surface area,with a contribution of more than 62%.The total pore volume and total specific surface area of the S-3 shale are larger,with an average value of 0.036 2 cm3/g and 35.15 cm2/g,respectively,while the total pore volume and total specific surface area of the A-1 shale are smaller,with an average value of 0.026 6 cm3/g and 21.39 cm2/g,respectively.Organic matter controls the specific surface area of the shale by controlling the development of micropores.In addition,Clay minerals have a cer-tain positive effect on the specific surface area of the shale,while pyrite has a certain promoting effect on the pore structure of M-2 and S-3 shale.The pore evolution of A-1 shale is most obviously affected by com-paction and clay mineral transformation,while the pores of S-3 shale are significantly influenced by cemen-tation,organic hydrocarbon generation and dissolution.The pores of M-2 shale exhibit both the diagenetic evolution characteristics of A-1 pores and S-3 shale.Conclusions The research results can provide refer-ence and guidance for the study of pore structure of coal-measure shale in the Ordos Basin.