Type-curve solution for coal seam degasification wells producing under two-phase flow conditions

In this paper a new series of type curves that can be used in the characterization of coalbed reservoirs are presented. The proposed type curves take into consideration the presence of water in the coal seam and its co-production with gas. The developed type curves are capable of handling the presence of the non-linear desorption phenomenon which plays a major role in the flow dynamics of methane in coal seams. A previously developed numerical model has been instrumental in the construction of the new type curves. During the development phase, gas and water equations were collapsed into a single expression. This consolidated transport expression was then put into a dimensionless form and necessary dimensionless groups were identified. The terms which relate to desorption process were included within the total system compressibility. This was made possible through a newly developed sorption functional group. The proposed type curves assume radial flow geometry around a degasification well which fully penetrates the formation. These type curves are generated for constant pressure specifications at the inner boundary. Coal seam initially is assumed to be in saturated state. The proposed type curves were tested extensively using a wide range of coal properties including desorption characteristics, and were identified with unique characteristics. The uniqueness of the type curves are preserved throughout the different flow regimes. The proposed type curve solution for coalbed reservoirs undergoing two-phase flow can be instrumental in analyzing the constant pressure drawdown test data from a degasification well.