Comparison of computation methods for CBM production performance
Mora, Carlos A.
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Coalbed methane (CBM) reservoirs have become a very important natural resource around the world. Because of their complexity, calculating original gas in place and analyzing production performance require consideration of special features. Coalbed methane production is somewhat complicated and has led to numerous methods of approximating production performance. Many CBM reservoirs go through a dewatering period before significant gas production occurs. With dewatering, desorption of gas in the matrix, and molecular diffusion within the matrix, the production process can be difficult to model. Several authors have presented different approaches involving the complex features related to adsorption and diffusion to describe the production performance for coalbed methane wells. Various programs are now commercially available to model production performance for CBM wells, including reservoir simulation, semi-analytic, and empirical approaches. Programs differ in their input data, description of the physical problem, and calculation techniques. This study will compare different tools available in the gas industry for CBM reservoir analysis, such as numerical reservoir simulators and semi-analytical software programs, to understand the differences in production performance when standard input data is used. Also, this study will analyze how sorption time (for modeling the diffusion process) influences the gas production performance for CBM wells.