Coalbed methane wells usually require a stimulation technique because their initial flow rates are often quite low. Hydraulic fracturing is the most common type of stimulation technique applied to coalgas reservoirs. Recently, open-hole cavity completions have become an alternative stimulation technique in coalbed methane reservoirs.

In this study, a three-dimensional, two-phase fluid flow model is used to compare production performances of the cavity-completed and hydraulically fractured wells in coalbed methane reservoirs. A static local grid refinement (LGR) technique is embedded into the model to adequately capture the flow behavior around cavity completions and hydraulic fractures without using excessively large number of grid cells.

The model utilizes a residual equation rather than a wellbore equation to determine the flow rates into the cavity and hydraulic fracture. Both cavity completions and hydraulic fractures are approximated as a combination of fine rectangular grid blocks. The constructed fine grid lines are terminated at the coarse and fine grid block interfaces by implementing the LGR technique developed. The generated flow equations for fine and coarse blocks are, then, solved simultaneously.

Flow performances of cavity completions and hydraulic fractures are compared for various coal seam permeabilities. It is demonstrated that permeability damage during fracturing may have significant impact on the flow performance of the hydraulic fracture. Hydraulic fractures without permeability damage associated perform better than cavity completions if permeability contrast in the coal seam is not significant. In strongly anisotropic systems, however, even if there is no formation damage due to fracturing fluid, cavity completions outperform hydraulic fractures.

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