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PERMEABILITY-POROSITY  RELATIONSHIPS             109


                             Equation 3.14 can be written as:








                             Substituting for svP from Equation 3.18 yields:







                             After the specific surface area per unit of pore volume, svP, is determined
                             from capillary data or petrographic image analysis (PIA),  then Equation
                             3.17 is used to obtain svg.


                             EXAMPLE

                               A core sample from a uniform sandstone formation has a permeability
                             of 480 mD and a porosity of 0.17. Estimate:


                             (a)  the average pore throat radius of the core;
                             (b)  specific surface areas svP and SV~.


                             SOLUTION

                               (a) Assuming the flow channels in the core sample may be represented
                             by a bundle of  capillary tubes, the pore throat radius can be estimated
                             from Equation 3.14. First, the permeability is converted from mD to pm2:


                             k = (480)(9.8717 x  lo-*) = 0.4738pm2


                             Solving Equation 3.14 for r:











                                              0.5
                             r= (  0.17  )       = 4.72 pm or 4.72 x  lo-* cm
                                   8(0’4738)
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