Seepage Model for Multiple-Fractured Horizontal Wells in Coal Bed Methane Reservoirs

Due to the features of low permeability and porosity, the horizontal well and fracturing treatment are effective ways to develop coalbed methane reservoirs, which have the large drain area leading to high producing rate and recovery. The seepage researches in conventional gas reservoir are sufficient, but there are few researches about the flow behavior and pressure distribution in coal bed methane (CBM) reservoirs, especially for multiple-fractured horizontal wells. In this work, based on the seepage theory, point-source function, and Laplace transforms, the mathematic models of gas flow in multiple-fractured wells are derived considering threshold pressure gradient and unsteady flowing. Subsequently, the type curves of multiple-fractured horizontal well in CBM reservoirs are obtained; there are main eight regimes. Finally, the mainly parameters affecting the dimensionless pressure and dimensionless pressure derivative are analyzed. The percolation characteristics of CBM reservoir are more complex than that of conventional gas reservoir for the presence of adsorption/desorption mainly affecting the seepage features in Middle-later Period and boundary behavior. This method does not only enrich our understanding of multiple-fractured horizontal well transport behaviors in coalbed methane reservoirs, but also has an important guiding significance for determining reasonable development program with multiple-fractured wells in the development of coalbed methane reservoir.