Electrochemical Modification on CH4 and H2O Wettability of Qinshui Anthracite Coal: A Combined Experimental and Molecular Dynamics Simulation Study

Abstract

The wettability of gas and liquid on the coal surface is one of the fundamental factors that affect the depressurization process during the coalbed methane (CBM) extraction. The wettability of coal surface changed after electrochemical modification, leading to the change in methane adsorption/desorption and water movement in coal reservoirs. Thus, the CH4 adsorption amount, desorption ratio, and coal–water contact angle of raw and modified anthracite samples were measured and simulated. The mechanism of electrochemical modification was analyzed by functional groups, surface free energy, pore characteristics, interaction energies, and coal swelling. The experimental results showed that the saturated adsorption amount of methane decreased from 41.49 to 34.72 mL/g, and the simulation results showed that the saturated adsorption amount of methane decreased from 2.01 to 1.83 mmol/g. The coal–water contact angle also decreased from 81.9 to 68.6°. Electrochemical modification mainly affects the wettability of CH4 and H2O by changing the functional groups and pore structures of anthracite, and the influence on functional groups of coal surface is greater. This work provided a basis for enhancing CBM extraction by electrochemical modification.