Constraint Mechanisms of Slug Flow Evolution on Gas-Liquid Transport in Microchannels of Coal Reservoirs

The key to stable production of coalbed methane (CBM) wells is governed by the dynamic coupling process of gas-liquid two-phase transport within the reservoir. The segmental plug flow that forms during the early stages of two-phase flow significantly restricts the gas-phase transport capacity, creating a bottleneck for accurately predicting CBM development. In this study, we employ an in-situ reservoir wettability testing technique to determine the coal-gas-liquid three-phase contact angle under reservoir conditions at the early stages of CBM development. We combine a microchannel model with microfluidic chip technology to prepare and modify the microchannel model, conduct gas-liquid segmented plug flow experiments, establish the pressure drop behavior under varying lengths of segmented plugs, and develop a level set model of the segmented plug flow based on flow parameters. We then analyze the pressure distribution characteristics within the channel interior. The study reveals that: (1) the in-situ temperature-stress coupling effect of the reservoir induces a subcritical transition in the wettability of the coal body, exhibiting characteristics of incomplete wettability weakening, which markedly differs from the strong hydrophilic state observed under conventional temperature and pressure conditions. (2) The pressure drop within the channel increases with the frequency of gas-liquid plugging units, and this nonlinear enhancement is governed by the synergistic amplification mechanism of the dynamic oscillation effect of the plugging flow and local turbulent dissipation. (3) The difference in curvature at the gas-liquid interface, along with liquid-film resistance, significantly exacerbates the accumulation of local interphase momentum dissipation, resulting in a reduction of the effective seepage cross-section rate and a mismatch between the apparent flow rates of the two phases. This study integrates in-situ testing of coal reservoir wettability with microfluidic technology to achieve precise characterization of gas-liquid segment plug flow under reservoir conditions, providing a theoretical foundation for stable production control and the efficient development of coalbed methane.