A review of laboratory study on enhancing coal seam permeability via chemical stimulation

•Chemical stimulation technology on ECBM recovery was reviewed.•The stimulation mechanism and interfering factor were compared.•Coal structure characterization methods were analysed.•The synergic treatment of chemical and physical stimulation was proposed. Chemical stimulation is a potential technology for coal permeability enhancement. Developing chemical stimulation techniques and understanding its mechanism are conducive to coalbed gas recovery enhancement and coal mining safety. Current researches primarily focus on the exploitation of various efficiently chemical stimulation techniques and the study on the mechanism of coal permeability enhancement. This article reviews recent laboratory researches on improving coal permeability by using chemical stimulation methods. The chemical stimulation mainly includes acidising, oxidizing, organic solvent extraction and electrochemistry stimulation techniques. Then, the interfering factors on efficiency of coal permeability enhancement including constitution and primary pore-fracture structure in coal, type of chemical reagent, formation of precipitation and in-situ stress, water blocking is analyzed based on the current laboratory researches. In addition, combined with challenges, the prospects of chemical stimulation field are proposed. Chemical stimulation techniques are still in the stage of theoretical and experimental research, and the field application research is insufficient. The field application research is required in future work to investigate the feasibility. The synergic treatment of chemical stimulation and physical stimulation techniques may have a greater efficiency on coal permeability enhancement and can be a prospective research.