Single-well Modeling of Coalbed Methane Production
The presented study concerns the unconventional coal bed methane (CBM) fields that imply peculiarity of their evaluation. The theoretical basis of the CBM field development is briefly described, most widely known models of changes in the properties of the coal seam are considered.
The study objective was formulation of a computation framework based on material balance equation and incorporating non-equilibrium nature of gas desorption, matrix shrinkage and geomechanically dependent relative permeability curves. Further solution of a specific CBM single-well problem and parametric study for evaluation impact of separate parameters were conducted.
Focus of the studies was on well production forecasting, effect of mechanical properties of coal on production efficiency, comparison of the analytical models performance based on specific mathematical models for absolute and relative permeabilities and residual saturations.
Numerical simulation is not flexible and easy to understand, therefore other tools are needed in order to try out the newly proposed mathematical models of processes occurring during CBM production. For desorption controlled reservoirs, considering non-equilibrium nature of desorption has to be essential, otherwise the production can be significantly overestimated. The currently proposed models have significant drawbacks, since they have to be heavily adapted to give similar results, being based on experimental results with limited pressures.