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Coalbed methane (CBM) is considered an unconventional gas resource produced from coal seams usually with low permeability at shallow depths. Analyzing the production performance in CBM reservoirs is challenging, especially at the early stages of recovery. Most of the small producers in the Appalachian Basin cannot afford personnel or meet economical requirements involved in the use of the numerical simulator to evaluate CBM reservoirs. Production type curves are an excellent tool for predicting the performance of CBM reservoirs. A set of type curves have been previously developed for horizontal and vertical wells in CBM reservoirs. The relative permeability characteristics have significant impact on the gas and water production due to the two-phase flow condition at the early stages of production. The impact of relative permeability on these type curves have been researched in this study.The values of relative permeability in coal bed methane reservoirs primarily depends upon 3 constants, which are n’, m’ and K. Using the relative permeability values from 4 different samples of coal, the range values for the three constants were obtained and the effect of these constants on the production type curves of gas and water were studied. It was concluded that both the gas and water production type curves were minimally affected by the variation of K. The effect of m’ was more influential in affecting the gas production type curves and the effect of n’ influenced the water type curves more. Also, a correlation among peak gas rate and constants governing relative permeability was developed. The correlation was validated and it showed accurate results with an error less than 10%.

The impact of relative permeability on type curves for coalbed methane reservoirs