Prediction of CBM well productivity under variable permeability

The accumulation characteristics and the percolation mechanism of CBM reservoir are different from those of conventional sandstone gas reservoir, resulting in big difficuty in productivity evaluation. The conclusion of investigation indicated that all previous researches have used material balance method or numerical simulation to predict the productivity. This paper builds up binomial deliverability model under the effects of turbulence by introdicing matrix shrinkage of multi-components of CBM, applied and analized the model in actual single well. The research results prove that coal reservoir permeability is affected by stress deformation and matrix shrinkage, decreases at beginning and increases later. And coalbed permeability recovery will be weakened more with higher impure content. Actual application demonstrated that productivity model for variable permeability can interpret well test data that conventional methods can't explain, the interpretation results can precisely assess the productivity of a CBM well.