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Darcy with Non-Darcy Dq Skin

 

 

 

NON-DARCY FLOW CONSTANT (1/mscfpd):  The empirical parameter relating the variable portion of skin factor to rate.  This value can also be estimated from equations (See Lee & Wattenbarger’s Gas Reservoir Engineering P.117).

 

RESERVOIR PRESSURE (psia):  The average reservoir pressure in the well's drainage area and can be obtained from pressure buildup analysis.

 

PERMEABILITY (md):  The absolute (i.e., fluid independent) permeability averaged over the net thickness of the zone.  These values are typically obtained from measurements on core samples using air as the fluid medium. Effective (i.e., fluid dependent) permeability estimates can be obtained from pressure transient analysis.  These estimates can then be converted to absolute permeability values.

 

WELLBORE RADIUS (ft):  The radius obtained from the caliper log, or the drill bit size when hole washout is not a problem.   The Wellbore Radius Examples  may be used as a  guideline.

 

EXTERNAL RADIUS (ft):  The distance between the well and the no-flow boundary created by off-setting wells in a developed pattern.   It is equal to one half the square root of the well spacing:  Rectangular drainage radius  =  0.5 * ( 43560 * A )    where A is the spacing (acres.) Drainage Area Examples

 

NET THICKNESS (ft):  The height or thickness of the zone believed to contribute flow.  It is usually obtained from well log analysis and should be consistent with the average permeability specified.

 

SKIN FACTOR:  A dimensionless number representing the near wellbore condition of damage or stimulation, where a  positive factor indicates damage and a negative factor indicates  stimulation.  This factor is obtained from pressure transient analysis of drawdown or buildup data.  It is important to remember that the completion effects are included in this number, i.e. horizontal wellbore, perforation density, gravel pack, etc..

 

WATER CUT:  The fraction of the total liquid flow stream that is made up of water.  In the results, fluid rate data is reported as TOTAL fluid, which includes this water cut fraction.