Influences of microwave irradiation on pore, fracture and methane adsorption of deep shale

Abstract

In order to better understand the feasibility of enhancing shale gas recovery by microwave irradiation, the influences of microwave irradiation on the pore, fracture, and methane (CH4) adsorption pertaining to shale gas production of a deep shale were fully addressed. A combination of multiple characterization methods was used, including pyrolysis, X-ray diffraction, back-scattered scanning electron microscope, probe molecule adsorption, steady-state permeability, X-ray computed tomography, and gravimetric method for measuring CH4 adsorption. Results show that microwave irradiation has no obvious impact on micropore but decreases mesoporous surface area, and volume of the shale matrix. It particularly reduces the adsorption pores for accommodating CH4 with the diameter of less than 8 nm. The nanoscale pore structure evolution is mainly associated with alterations in organic matter and inorganic minerals of the deep shale after microwave irradiation. Microwave irradiation induces the decomposition, cracking, shift, stripping and formation of minerals, as well as the formation of organic matter. Furthermore, it significantly increases fractures paralleling to bedding planes of the deep shale due to thermal stress generated within various minerals. These newly formed fractures dramatically increase the porosity and permeability of the deep shale. Finally, microwave irradiation significantly decreases the maximum CH4 adsorption capacity of the deep shale by 16.38%. In summary, this study put forward a novel method for enhancing shale gas production via simultaneously promoting CH4 migration and reforming reservoirs under controlled microwave field.