Page 152 - Petrophysics 2E

PERMEABILITY-POROSITY RELATIONSHIPS 125

sandstone formation. The intercept at ,@ = 1 may be used to calculate
the free fluid index, which in turn can be used to estimate an average
value of irreducible water saturation for the entire flow unit or reservoir.
A log-log plot of RQI versus @ should also yield a straight line with the
same intercept, but with a slope of 1.5.

EXAMPLE

(a) Estimate the permeability (mD) of a reservoir rock that has a porosity
of 15% and an irreducible water saturation of 24%.
(b) Assuming this permeability is representative of the flow unit,
calculate the reservoir quality index RQI (pm).
(c) Calculate the flow zone indicator FZI.
(d) Calculate the Tiab flow unit characterization factor HT.

SOLUTION

(a) The free fluid index is calculated from Equation 3.57:

=
FFI = (1 -GI)@ (1 - 0.24)(0.15) = 0.111
The permeability is estimated from Equation 3.58:

(b) The reservoir quality index RQI is calculated from Equation 3.59:

+ - FFI

= 3.14 (o.l;~llll) -= 0.519pm

Equation 3.43 also yields the same value:

RQI = 0.0314 /: - = 0.0314 ,/:t5 - - -0.519pm