Modeling Liquid Loading Behavior in Coalbed Methane Gathering Pipelines

With the maturation of coalbed methane (CBM) exploitation and the transition into the late stages of dewatering and gas production, liquid loading in gathering pipelines has emerged as a major constraint on productivity and operational stability. Based on real-time field data and gas–liquid physicochemical analyses, this study elucidates the mechanisms governing liquid loading formation under varying temperature, pressure, and water saturation conditions. An HYSYS model is employed to determine the water dew point, while the Turner model is used to evaluate the critical conditions for liquid holdup. The results indicate that gas water saturation exerts the dominant influence on liquid loading risk, followed by pressure, whereas temperature plays a comparatively minor role. When water saturation exceeds 2% and the operating temperature falls below the dew point, condensation-driven liquid loading increases sharply. To further characterize the spatial distribution of liquid accumulation, a steady-state OLGA model of a DN100 gathering pipeline network is developed to examine the effects of pipe diameter, water saturation, and soil temperature. The simulations show that larger pipe diameters and higher water saturation significantly aggravate liquid holdup, while elevated soil temperature mitigates liquid accumulation. Moreover, the liquid holdup ratio is found to correlate closely with flow regime transitions, confirming its suitability as a key indicator of liquid loading risk. Based on these findings, optimization strategies for pipeline design and operation are proposed. To mitigate liquid loading, the gathering pipeline velocity should be maintained above the critical value of 1.63 m/s, and the gas water content should be strictly controlled below 2%. Under operating conditions representative of the Hancheng block, it is recommended to reduce the pipeline diameter from DN130 to DN100 to enhance self-cleaning capacity. In addition, thermal insulation should be applied during winter operation to maintain the pipe wall temperature above 10°C, thereby suppressing condensation-induced liquid accumulation.