We study the effects of coal wettability on gas bubble/water two-phase flow behaviour in micro-cleats of the coal seam gas reservoir using a free energy based two-phase lattice Boltzmann model. The model is validated by comparison with analytical results and published results, and good agreement is achieved in general. Then we use this model to simulate bubble-water flow in both smooth capillary and a capillary with a narrow throat to systematically study the influences of contact angle, capillary pressure and bubble size on the flow behaviour. The simulation results indicate that both the bubble size and contact angle have significant impacts on the flow capacity of bubble and water, especially in a channel with a narrow throat. A decrease in water flow rate is observed when larger bubbles occur, and the water flow rate increases when the gas wettability becomes stronger. The bubble flow dynamics significantly influence the drainage of water and the further gas production. (C) 2016 Elsevier Ltd. All rights reserved.