The Perturbation Solution of Unsteady Seepage in Coalbed Methane Unsaturated Water Flow Phase
Sun Keming, Liang Bing, Xue Qiang
(Dept. of mechanics, Liaoning Technical University, Fuxin 123000)

Abstract: Coalbeds are characterized by their dual porosity, which contains both matrix and cleats porosity systems. The matrix porosity system contains the vas t majority of the gas volume, while the cleats porosity system provides the conduit for mass transfer to the wells. Coalbeds methane flow through cleats to production wells includes three phases: single-phase water flow and both unsaturated water flow and saturated water flow. In the unsaturated water flow phase, when the cleats system pressure drops, gas molecules desorb from the matrix porosity interface and are released into cleats porosity system. As a result, desorbed gas forms discontinue gas bubbles, which hold back water flow. At the same time, the coalbeds methane transport includes the coupling process of seepage field, deformation field and stress field. In the paper the fluid-solid interaction and desorbed gas affect water transport are analyzed. A coupled mathematical mod el of unsteady seepage in coal methane unsaturated flow phase is established based on the theory of fluid-solid interaction. The nonlinear mathematical model is investigated by using the perturbation and integral transform. Pore pressure along level distance at different saturation and time, and gas phase effect on seepage flow under coupling and without coupling conditions are discussed. Some valuable conclusions were got.
Keywords: Unsaturated water flow phase, fluidĒ˛solid interaction , unsteady seepage.