The injection of CO₂ into shale gas reservoirs can not only enhance shale gas recovery (ESGR), but also realize CO₂ geological storage (CGS). In this study, the competitive adsorption behaviors of CO₂ and CH₄ in shale were systematically reviewed, and the implication for shale gas recovery efficiency and CO₂ storage potential were discussed. The adsorption advantage of shale for CO₂ compared to CH₄ provides a guarantee of the feasibility of supercritical CO₂ (ScCO₂) enhanced shale gas exploitation technology. The selective adsorption coefficient of CO₂ and CH₄ by shale (S CO₂/CH₄ ) is an important parameter in evaluating the competitive adsorption behavior of CO₂/CH₄ in shale gas reservoirs, which is closely related to the mineral composition, reservoir temperature, pressure conditions, water content, and mixed gas composition ratio. In addition, the injection type, injection mode, and injection rate of gases also exhibit different effects on CO₂/CH₄ competitive adsorption. Furthermore, the interaction between ScCO₂ and the water-rock system will change the mineral composition and microstructure of shale, which will lead to changes in the adsorption behavior of shale on CO₂ and CH₄, so its influence on the competitive adsorption of CO₂/CH₄ cannot be ignored. Future research should integrate different research methods and combine with practical engineering to reveal the competitive adsorption mechanism of CO₂/CH₄ in shale reservoirs from both micro and macro aspects. This study can provide support for the integration technology of ScCO₂ enhanced shale gas exploitation and its geological storage.

Power ultrasonic-assisted reservoir modification is a promising technique for enhanced coalbed methane recovery. However, the in-site performance of ultrasound-assisted CBM production has not yet been revealed. In the current study, the in situ antireflection test was conducted with high-power ultrasound ~18 kW in underground coal seam, and the antireflection performance was investigated by measuring the borehole drainage gas data in the field test zone, and then, the in situ permeability change of the target coal seam was evaluated numerically. The result shows that, within 40 days’ drainage after ultrasonic antireflection in coal seam, the average gas concentration of single borehole in the experimental group increased by 81.4 %~227.3% than that in control group, the average borehole gas flowrate has a 20%~106% improvement over the control group, and the pure methane production in single borehole increased by about 3.83 times. The permeability inversion indicates that the in situ coal seam permeability has increased by at least 2.36 times after the ultrasound stimulation within the range of 8 m from the ultrasound source.