PERMFILE49521

• Permit No: M1999002
• IBM Index Class Name: Permit File
• Doc Name: Reference: NUCLEAR WELL LOGGING
• Media Type: D
• Archive: No

158 NUCLEAR WELL LOGGING 4
The photo in Fig. 4.4a represents the sonde used in the well.
The investieation radius is approximately 15 cm (6").
An example of the log is given in Fig. 4.5. The caliper can be seen on the le(thand track
and the bulk density curve on the righthand ones.
Density logs have become very important because they can be used to:
(a) Determine a "density" porosity which is indispensable for modern interpreting.
(b) Specify the lithology and a good value of the porosity, in conjunction with a neutron
or sonic log.
(c) Detect the presence of gas in the invaved zone because it causes a sharp decrease in
the density and hence an abnormally high apparent "density porosity".
Since the tool used has a pad, a caliper log recorded at the same time indicates the
presence o(a mud cake or cave-ins.
4.3.2. Litho-Density log
A selection o(the IoW-enerey gamma rays arrivine at the counter on the sonde shown in
Fig. 4.4b can be used to measure the"photoelectrice(fect" or"photoelectric absorption"
linked to the averaee atomic number of the nuclei o(the atoms in [he (ormation. Figure 4.5
is an example o(aLitho-Density log.
The curve in Fig. 4.6 represents the photoelectric absorption factor (Pe) of the
formation:
Z J.fi
Ze f~, is the efTective atomic number which is the mean atomic number of all the atoms in
the medium being considered.
Table 4.1 gives the photoelectric absorption factor (PQ), the density (pb) and the U (actor
for different bodies commonly encountered in boreholes:
TABLE 4.1
Minerals P, pa U
Quartz ............................... 1.81 2.64 4.78
Calcite ............................... 5.08 2.71 13.77
Dolomite ............................ 3.14 2.88 9.00
Anhydrite ............................ 5.05 2.98 14.95
Halite ............................... 4.65 2.04 9.68
Siderite .............................. 14.70 }.89 55.90
Pyrite ............................... 17.00 4.99 82.10
Barite ............................... 267.00 4.09 1065.00
Chlorite (') ........................... 6.30 2.79 17.58
Illite (') .............................. 3.45 2.52 8.69
Kaolinite (') .......................... 1.83 2.41 4.41
Montmorillinite (') .................... 2.04 2.12 4.32
I. Approximate ~~alues.
4
CALIP
GAMb