Page 127 - The Geological Interpretation of Well Logs

- THE DENSITY AND PHOTOELECTRIC FACTOR LOGS -

Table 9.2 Density, electron density and tool given density for some common compounds (from Schlumberger, 1989a).

Compound Formula Actual density Tool density based on *Density given on
p,, g/cm? electron density (pe), g/cm ~— log g/cm?

Quartz SiO, 2.654 2.650 2.648
Calcite Caco, 2.710 2.708 2.710
Dolomite CaCO,MgCO, 2.850 2.863 2.850

Halite NaCl 2.165 2.074 2.032
Gypsum CaSO,2H,0 2.320 2.372 2.381
Anhydrite CaSO, 2.960 2.957 2.977
Sylvite KCI. 1.984 1.916 1.863

Coal bituminous 1.200 1.272 1.173
1.500 1.590 1.514
Coal anthracite 1.400 1.442 1.355
1.800 1.852 1.796

Fresh water H,O 1.000 1.110 {.000
Salt water 200,000 ppm 1.146 1.273 1.135
Oit n(CH,) 0.850 0.970 0.850
Methane CH, 0.000677 0.00084
Gas C, Ay, 0.000773 0.00096

*Density given on log = 1.0704 (pe) — 0.1883

. TOOL
Table 9.3 Moder density tools,
1, Density measurement f y

Name Symbol Company
GAMMA RAY

Formation Density -
Compensated FDC Schlumberger rr SOL HEAD
Compensated Densilog CDL Western Atlas, Halliburton HO ‘e chematic)
Compensated Density CDS BPB

2. Density and Photoelectric measurement

Name Symbol Company
GAMMA Ray

Litho-Density Tool LOT Schlumberger ee 303m)
Compensated Z-Density ZDL Western Atlas
Photoelectric Density PDS BPB compensated
Spectral Density Toot HSDL Halliburton W338 wm}
long spacing

detector

far detector response enhance the formation effects short spacing
(Figure 9.6). The most recent density tools (Table 9.3) use detector
more efficient scintillation detectors which separate high
(hard) and low (soft) gamma ray energy levels (Figure source
9.3). This allows a better evaluation of borehole effects, so
providing a more accurate density measurement as well as OE ONY
the additional photoelectric factor value (Section 9.7). x flea gem) 77
Source and detectors are mounted on a plough-shaped pad
which is pressed hard against the borehole wall during Figure 9.4 A density tool (Densilog from Atlas Wireline) and
logging (Figure 9.4). Density-log readings therefore refer a tool head (modified frorn Dresser Atlas, 1982 and Ellis,
1987).
to only one sector on the borehole wall.
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