The role of residual bitumen on the pore structure of organic-rich shales from low to over mature: Insight from shale and coal samples after the hydrous pyrolysis

The role of residual bitumen on the pore structure of organic-rich shales is related to maturity. However, the studies about the role of the soluble and insoluble residual bitumen on the pore structure of organic-rich shales from low to over mature are deficient. In this study, non-extracted and extracted organic-lean shale, organic-rich shale and coal samples after the hydrous pyrolysis are used to investigate the role of residual bitumen on the pore structure of the organic-rich shales from low to over mature. The specific surface areas of shale and coal samples from low to over mature increase after the solvent extraction. For the organic-lean shale samples from low to over mature and the organic-rich shale samples (lower than 1.51% Ro), the increments of the specific surface area are in proportion to the extractable organic matter (EOM) contents. For the coal samples from low to over mature and the organic-rich shale samples (higher than 1.51% Ro), there is no positive relationship between the increments of the specific surface area and the EOM contents. The increments of pore volumes are obvious in the organic-rich shale samples from mature to high mature and coal samples at wet gas and dry gas stage. The blocking of soluble residual bitumen on inorganic nano-pores depends on the EOM content and will reach the top at the maximum EOM content or the oil peak while the blocking of soluble residual bitumen on organic nano-pores does not depend on the EOM content and will reach the top at over mature. From low mature to mature, the soluble residual bitumen only blocks inorganic nano-pores. From high to over mature, the blocking on inorganic nano-pores gradually becomes weak while the blocking on organic nano-pores gradually increases. The scanning electron microscopy observations and the thermal evolutions of the specific surface area/pore volume of the non-extracted organic-rich shale and coal samples indicate that the organic nano-pores of the insoluble residual bitumen are undeveloped from low mature to mature and more and more developed from high to over mature.