Influences of controlled microwave field radiation on pore structure, surface chemistry and adsorption capability of gas-bearing shales

Abstract

Aiming to explore the feasibility of using microwave field radiation to produce shale gas via temperature swing. The heating behaviors and alterations in physicochemical properties and adsorption capability of gas-bearing shales under the controlled microwave field are preliminarily investigated. Results indicate that the shales can significantly absorb microwave energy. The bulk temperature of shales increases with the duration of microwave radiation. The heating behaviors of shales under the controlled microwave field are probably associated with pyrite and marcasite contained in shales, which greatly determine the complex permittivity and thermal conductivity of shales. Next, the microwave radiation decreases the adsorption pores with pore width below 10 nm, and fractal dimensions of pore surface and pore structure of the shales determined from the Neimark model and the FHH model, while increases the amount of meso- and macropores with pore width above 10 nm, MIP total pore volume and porosity of shales. These alterations in pore structure promote desorption and migration of shale gas within reservoirs. Furthermore, the microwave radiation changes the surface chemistry property of shales. The FTIR analysis reveals that the total content of CO and COOH of shales grows after the microwave radiation, whereas the aromaticity decreases. The alterations in both oxygenic functional groups and aromaticity are prone to promote shale gas desorption from shale matrix by weakening the intermolecular force between shale gas and shale matrix. Finally, the microwave radiation decreases the maximum CH4 adsorption capacity of the shales, the decreasing amplitude of which is 12.70–47.83%. In conclusion, the aforementioned heating behaviors and alterations in physicochemical property and adsorption capability of shales under the controlled microwave field imply that microwave radiation is an alternative option to enhance shale gas production.