Page 547 - Petrophysics

5 14 PETROPHYSICS: RESERVOIR ROCK PROPERTIES

resistivity = 85 ohm-m. The reservoir average porosity (17%) was
determined from a Neutron log. Substantial mud loss was observed during
drilling of this well as well as in neighboring wells. Pressure test analysis
as well as cores confirmed the presence of extensive natural fractures in
the well.

(a) Estimate the fracture intensity index and the porosity partitioning
coefficient.
(b) If the average irreducible water saturation estimated from log analysis
is 24%, determine the fracture width. Note that the coefficient CX in
equation 8.12 is typically 0.25.
(c) Estimate the fracture width, fracture permeability and fracture
porosity of the formation.

SOLUTION

(a) Knowing RLLS = Rxo = 12 and Rm = Rt = 85, the fracture intensity
index is estimated from Eq. 8.18:

1 I

FII = Rxo Rt - 1/12 - 1/85 = 0.1417
1 1 - l/0.165 - 1/0.18

The saturation of mud filtrate in the flushed zone is:

S,, = S2 = 0.24°.25 = 0.70

The porosity partitioning coefficient is calculated using equation 8.13:

- 0.18 (L - ifi) = 0.165
-
O.li’(0.24 - 0.70) 85

(b) Using Equation 8.19a:

0.064
[(l
Wf = - - Siw)FII]1.315
ot
0.064
- -- [(l - 0.24)(0.1417)]’.315 = 0.02 cm
0.17