Comparative experimental study on porosity, mechanical and CO2 adsorption characteristics of coal and shale

To compare the pore structure, mechanical and CO2 adsorption properties of coal and shale, a series of experiments were carried out using nuclear magnetic resonance (NMR), uniaxial compression, Brazilian splitting, and high-pressure CO2 adsorption. The results show that the total porosity of coal is 7.51 times that of shale, and shale is dominated by adsorption pores, while adsorption pores and seepage pores in coal are equally important. Moreover, it is found that the micropores in shale are more advantageous, while meso-macropore in coal are more significant. The adsorption pore surface of coal is rougher than that of shale, and the seepage pore structure of shale is more complex. The uniaxial compressive strength, elastic modulus and absorption energy of shale are 2.01 times, 2.85 times, and 1.27 times that of coal, respectively, indicating that shale has higher compressive capacity and resistance to elastic deformation than coal. The average tensile strength, Brazilian splitting modulus, absorbed energy and brittleness index of shale are 7.92 times, 6.68 times, 10.78 times, and 4.37 times that of coal, respectively, indicating that shale has higher tensile strength and brittleness, but lower ductility, compared with coal. The performed analyses show that under the same conditions, the CO2 adsorption capacity of coal is greater than that of shale. The present article can provide a theoretical basis to implement CO2-enhanced coalbed methane (CBM)/shale gas extraction.

Automated summary

A series of experiments were conducted to compare the pore structure, mechanical properties, and CO2 adsorption properties of coal and shale. The results showed that coal had a higher total porosity compared to shale, with both types of pores being important. Shale had more advantageous micropores, while coal had more significant meso-macropores. Shale also exhibited higher compressive strength and resistance to elastic deformation, while coal had higher tensile strength and brittleness. Additionally, coal had a greater CO2 adsorption capacity compared to shale. These findings provide a theoretical basis for implementing CO2-enhanced coalbed methane (CBM) and shale gas extraction.