Pore Structure and Adsorption Characteristics of Marine and Continental Shale in China

Typical marine shale samples from the Sichuan Basin and continental shale samples from the Ordos Basin were taken to investigate the effect of pore structure characteristics on the gas sorption of shales. Field emission scanning electron microscope (FE-SEM) and low pressure N-2 isotherm were used to characterize the pore structure. High pressure CH4 and CO2 adsorption was conducted in pressure up to 12 MPa and at temperatures of 35 degrees C, 45 degrees C, and 55 degrees C, respectively. The results indicated that the specific surface area (SSA) of the continental shale is much lower than that of the marine shale samples. The SSA of micro (pore size <2 nm) and mesopores (2 nm < pore size <50 nm) accounts for over 80% of the total SSA in marine shale, while the SSA of micropores in the continental shale is probably insignificant. And the CH4 and CO2 sorption capacities of marine shale samples are higher than that of continental shale samples. The adsorption capacity of CH4 exhibits a positive correlation with specific surface area and fractal dimension. As the temperature increases, the gas adsorption capacity and Langmuir volume decrease, but the Langmuir pressure (P-L) increases. In addition, the CO2 adsorption capacity is nearly 2-4 times higher than the CH4 adsorption capacity, indicating favorable potential of using CO2 to enhance shale gas recovery.