Investigation on the Concentration Characteristics and Distribution of Coal Fines in a CBM Vertical Wellbore

The production of coal fines during the drainage of coalbed methane (CBM) wells in the southern Qinshui Basin severely restricts gas production. This study systematically investigates the distribution characteristics of coal fines concentration by integrating field sampling, laboratory testing, physical simulation, and numerical simulation. The results show that the wellhead coal fines concentration in the study block ranges from 0.125 to 7.195 g/L, with an average of 1.055 g/L. Physical simulation reveals that the coal fines concentration within the wellbore decreases progressively from the bottom to the top, and the overall concentration increases synchronously with the injection concentration. The numerical model established using Fluent software (version 2021 R1, ANSYS, Inc., Canonsburg, PA, USA) shows good agreement with the physical simulation results. Based on the numerical simulation data, a distribution model for coal fines concentration in a 1000 m full-scale wellbore is constructed, and the empirical model is expressed as Y=17.978X−0.114 (R2=0.8713). This study reveals the distribution pattern of coal fines concentration in the wellbore, providing a theoretical basis for coal fines control and the optimization of drainage and production strategies in CBM wells.