REVISED
© 2003 - 2007 WELLOG
All Rights Reserved
PART II, PAGE 4
COMBINATION POROSITY LOGS:
Compensated Neutron porosity (apparent limestone) and Acoustic velocity
(Dt)
combination:
Corrections are applied to correct the compensated neutron
log for other matrices using information from the
Acoustic log.
Dolomite - Limestone:
A two step procedure is performed;
Step 1: The
calculation for f(corr)
in Dolomite is performed using apparent neutron porosity, f(CN).
Assuming: Dt (f) = 189 usec/ft.
((Dt Dt(lms)) f(dol) f(CN) (Dt(dol)
Dt(lms))
f(corr) = ---------------------------------------------------
((D(f) Dt(lms)) f(dol) 100 (Dt(dol) Dt(lms))
Step 2: The
calculation for matrix porosity is made using the corrected porosity f(corr) found in step 1.
When f(corr) < 4 percent, the porosity in dolomite is calculated from
the equation:
f (dol)
= 100 - (101.64 (f /.0311 +
6.97))1/2 /(100
- <f) x 100
When f(corr) > or = to 4 percent, the porosity in
dolomite is calculated from the equation:
f (dol)
= 100 - ( 94 f) / (100 - f ) x 100
Sandstone - Limestone:
A two step procedure is performed;
Step 1: The
calculation for f(corr)
in sandstone is performed using apparent neutron porosity f(CN).
Assuming: Dt (f) = 189 usec/ft.
(Dt Dt (lms))
x f(sd) f(CN) x (Dt (sd)
Dt (lms))
f (corr) = -------------------------------------------------------
(Dt (f) Dt (lms))
x f(sd) 100 x
(Dt (sd) Dt (lms))
Step 2: The calculation
for matrix porosity is made using the corrected porosity found in step 1.
f (sd) =
(104 f) / (100 f) x 100
CROSS PLOT:
Cross plots were given early consideration in Openhole crossplot Concepts a
powerful technique in Well Log Analysis in the Journal of Petroleum
Technology, Vol. 33, March, 1981 pages 535-549, By Walter Fertl.
For information on cross plot techniques, go to cross plots.