Page 133 - The Geological Interpretation of Well Logs

- THE DENSITY AND PHOTOELECTRIC FACTOR LOGS -

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GAMMA RAY 2 BULK DENSITY
API x gicm*
0 50 wol § |r.96 2.2 2.45 27]

= -

20

30m

ee
=

Figure 9.14 Thin, carbonate/siderite cemented horizons ta shale. The intervals may be thin
continuous bands or irregular, nodular horizons.

3 | BULK DENSITY g/em®
5 21 22 23 24 25 26 27

a 7 : ; + 9 LITHOLOGY

ins
uy
14
o12
19
SAND
Figure 9.16 Secondary calcareous cementation in sandstone.
SHALY | L
SAND : | ° secondary, diagenetic
(same mica) f: cemented zones 10m
|
|
|
The density log shows thin, cemented intervals which have
|
|
little or no porosity while the reservoir generally has 30% —
- 20
|
35% porosity.
MICACEOUS|::
SAND !
Table 9.6 Diagnostic mineral and lithological densities (from
|
Serta, 1972, 1979; Gearhart, 1983; Dresser Atlas, 1983).
|
| | | | | 20m Low Lignite (g/cm?)
|

0.50-1.50
Coal
1.15-1.70
Anthracite 1,15-1.70
Organic shale 1.80-2.40
dum bulk density of non-micaceous
sands (@ 24%)
High Pyrite 4.80-5.17
Figure 9.15 The effect of muscovite (grain density 2.76 - 3.1
Siderite 3.0-3.89
g/cm?) on the bulk density log in micaceous sands. The
increase in density below 15m is due to the mica content, Basalt 2.70-3.20
The percentage of mica indicated is based on thin-section Gneiss 2.60-3.04
analysis of core material.
2.3g/cm*). Coals, for example, are identified by very low Evaporite identification
densities, between 1.2g/cm* and 1.8g/cm*, and pyrite, Chemical deposits, because of their purity, may at least be
conversely, by very high densities, between 4.8g/cm* and suspected if not positively identified by their densities (Table
5.17g/em*. The extreme values for these minerals may 9.7). Care must be taken, as evaporites may be impure and
not be reached under natural conditions, but abnormally densities will be altered. However, most evaporites tend to
high and abnormally low peaks are still easily visible give intervals of constant density with very litle variation.
(Figure 9.17). The more common extreme and diagnostic When this occurs, along with densities near the pure
densities are shown above (Table 9.6). mineral values, evaporites are probable (Figure 9.18).
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