Page 255 - Petrophysics 2E

228 PETROPHYSICS: RESERVOIR ROCK PROPERTIES

SOLUTION

(a) Formation resistivity:
Rosales formula for consolidated sandstones, i.e., Equation 4.47,
gives:

FR = 1 + 1.03(0.216-'.73 + 1) = 14.57

Humble formula (Equation 4.39) gives:

FR = (0.62)0.216-2.'5 = 16.72
Because Berea cores are generally moderately to strongly cemented,
one can use m = 1.7 in the Archie formula:

FR = O.216-l.' = 13.53

It is obvious that the value of FR obtained from the Archie equation
is the closest to the measured value. Thus, the Archie formula is a
good model to use for calculating the formation resistivity factor of
a Berea Sandstone core. The value of the cementation factor for this
core is:

In 13.7
m= = 1.71
In 0.216
(b) The flowing porosity is approximated from Equation 4.43:

Och = 0.216'.71 = 0.073

and from Equation 4.41, the stagnant porosity is equal to:

$tr = 0.216 - 0.073 = 0.143
This means that only 34% [(0.073/0.216)(100)] of the total pore
volume participates actively in the flow of electric current and 66%
of the pore volume, corresponding to the dead-end and symmetrical
traps, is neutral to the flow of electric current. If the flow of viscous
fluids were considered, instead of electric current, different results
would have been obtained, i.e., higher Och and lower because
viscous forces, such as capillary forces, promote the transfer of
a fraction of the fluid in stagnant regions to the flowing regions [ 111.
(c) The tortuosity of this Berea Sandstone core can be obtained from
Equation 4.52:

0.143
=
z = 1 + - 2.96
0.073