(5)--5-Non-Darcy Flow气藏工程气藏工程.ppt

5.5 Non-Darcy Flow5.5 Non-Darcy Flow The transient pressure response of a gas well may be affected by high velocity or non-Darcy flow near the wellbore In terms of adjusted pressure,the unsteady-state flow equation becomes:Apparent Skin FactorEffective skin factor includes true formation damage and the effects of non-Darcy flowNomenclature:s-“true”skin due to damage or stimulation,dimensionlesss-apparent or effective skin factor that would be measured during flow or buildup test,dimensionlessD-non-Darcy flow coefficient(assumed constant),D/Mscfqg-gas flow rate,Mscf/DThe“true”skin due to damage or stimulation cannot be obtained from a single constant-rate test.Method 1:Estimating Non-Darcy Coefficient from Multiple Tests024681002,0004,0006,0008,00010,000Flow rate,Mscf/DApparent skin factors=3.4D=5.1x104D/MscfMethod 2:Estimating Non-Darcy Coefficient from Turbulence ParameternOften,only one test is availablenIf so,we can estimate D fromkg-effective permeability to gas,md-turbulence parameter,ft-1g,wf-gas viscosity at flowing bottom hole pressure pwf,cpEstimating Turbulence ParameterIf is not known,it can be estimated fromWarning!This provides only a very crude estimate of the magnitude of the turbulence parameter.Further,it assumes that non-Darcy flow occurs in the formation near the wellbore rather than through the perforations.5.5 Non-Darcy Flow（End)