Anti-channeling methods for coalbed methane production using L-type horizontal wells

Coalbed methane (CBM) production using L-type horizontal wells can yield stable single-well production of up to above 8 000 m³/d. However, due to the lack of sand settling pockets, L-type horizontal wells fail to achieve gas-water separation under the action of gravity. Consequently, gas channeling from tubing is prone to occur, significantly decreasing pumping efficiency and restricting further drainage and pressure reduction. By optimizing the lifting process for production in the early stage, the gas channeling from tubing has been somewhat alleviated. However, the anti-channeling effects remain unsatisfactory in low-fluid-pressure and high-yield gas wells. This study examined L-type horizontal wells in the Fanzhuang-Zhengzhuang block within the Qinshui Basin. Based on the changing patterns of gas and water in 56 wells subjected to gas channeling from tubing, this study established evaluation indicators for gas channeling severity. Using grey relational analysis, this study identified dominant factors influencing gas channeling from tubing, determining the causes. Furthermore, this study proposed two methods for preventing and controlling gas channeling from tubing to optimize the production system. Key findings are as follows: (1) The annular liquid column height in the wellbore is proved to be the prerequisite for gas channeling from tubing. Gas channeling from tubing can occur suddenly with a decrease in the liquid column height. Liquid column heights above 75 m suggest the absence of gas channeling or the occurrence of mild/moderate gas channeling primarily at the outlet, while those below 75 m are predominantly associated with severe gas channeling. Moreover, gas channeling severity increases exponentially with a decrease in the liquid column height. (2) The gas-liquid ratio is identified as a critical factor affecting gas channeling severity, which increases logarithmically with the former. Gas-liquid ratios below 30 suggest mild/moderate gas channeling primarily, whereas those above 30 are principally associated with severe gas channeling. (3) The pressure-controlled drainage method, by remaining constant high casing pressure, can effectively enhance the liquid holdup of the two-phase flow near the pump inlet. The production-controlled drainage method, by controlling the daily gas production, can reduce the gas-liquid ratio near the pump inlet to below 30. Both methods, which can effectively alleviate the gas channeling from tubing, combined with the anti-channeling lifting process for production, can jointly eliminate gas channeling from tubing.