An experimental study of the effect of electric field enhancement on the adsorption characteristics of coalbed methane

Due to the specific reservoir characteristics of coalbed methane (CBM) in Qinshui Coalfield of Shanxi Province, the scale of gas drainage in coal mines is limited and CBM extraction remains challenging. In an effort to modify the adsorption performance of coalbed gas and enhance CBM recovery, the application of an external electric field as a stimulating method was investigated. This study focuses on #9 and #15 anthracite samples from the southern part of Qinshui Coalfield. Comprehensive coal quality analyses were conducted. An experimental device was developed to study CBM adsorption under the influence of electric fields, which served as an external physical stimulation field. Using this apparatus, adsorption isotherms, the maximum adsorbed quantity, and an empirical adsorbed constant of #9 and #15 coal samples were experimentally determined. Based on pore structure parameters, the influence of electric field enhancement on CBM adsorption was examined.The results indicate that electric fields significantly reduce CBM adsorption capacity compared with before the action of an electric field. With increasing electric field strength, the maximum adsorbed quantity decreases linearly, while the empirical adsorbed constant decreases exponentially. The reduction in CBM adsorption capacity following electric field treatment is attributed to the increase in median diameter of mesopores in coal, which lowers the surface potential energy of pores in coal, thus reducing its adsorption capacity for methane.Furthermore, the increase in the median pore diameter is more conducive to the migration and diffusion of methane gas, thereby improving the methane extraction rate and extraction efficiency. This study has certain theoretical significance for the extraction of methane from CBM reservoirs with low pressure and low permeability.