Responses of specific surface area and micro- and mesopore characteristics of shale and coal to heating at elevated hydrostatic and lithostatic pressures

A sustained hydrostatic pressure increase from ambient to 300 MPa for 6 to 12 months resulted in insignificant changes in vitrinite reflectance values. Small differences in Brunauer-Emmett-Teller (BET) specific surface areas, micropore surface area, and volume may be related to internal sample heterogeneity rather than pressure treatment. Similar to the temperature effect, the Wilcox Coal sample experienced more pronounced changes compared to the shales. SEM observations on shales did not reveal porosity-related changes between the original and treated samples. No marked changes were documented for lithostatic pressure conditions at 100 MPa and 100 °C. We conclude that elevated isotropic hydrostatic or lithostatic pressure is unable to significantly affect the pore structure and pore-size distribution of shales, but it can make some modifications in the micropore and mesopore pore characteristics of low-rank coal.