Page 39 - The Geological Interpretation of Well Logs

- CALIPER LOGS -

B
A CALIPER DIFF. CALIPER
inches LITHOLOGY inches
2500m

LITHOLOGY
WNT
4 4

bit size iv
4 aliper

Ma wn
caliper 900m ——————_1»
¥
r

py ¢

i oyral]
tight
T VP
i
sandstones i ‘a \
mud spots il clays swelling

cake
permeable smectite-rich
\

and porous

2525m —_——_—————___—_—_
950m

Figure 4.6 Hole size diminution seen on the simple caliper. (A) Mud-cake build-up opposite porous and permeable sandstones. i
(B) Tight spots in a shale sequence caused by hole sloughing due to swelling clays.

>
2
3°

CALIPER OENSITY LOG 3a DENSITY LOG SONIC LOG
inches CORRECTION z aicm3 wétt
2-01 0 0,1 Ss WT 2.21160 90
650m a iti 1

'
cavo-induced|y
{bit size~| !—— catiper HOLE CREATED
:
bough c TROUGH

| cave — —

f uncompensaled
' cave

|
4 !
i
& i 5
e ! ‘, —
» 1
) ;
| 1 \
Pa i low density
4 i
4 Se Mess, from caving] ¢ HOLE CREATEO
; f TROUGHS
1 .

a a Se 4 high sonic
<2" - : <a from caving
<4 Lg =
7 mex 4 3 NOT REAL
SB
a
VALUES
room g 3) | Se aa _— FORMATION
=~
4 ast k a =

Pe
Zz
‘

bit sixo 174 mud density 1.38 gem?
Figure 4.7 Poor hole conditions and caving creating zones of poor data quality where fog readings do not represent real formation
values. The automatic density correction derived from the caliper is insufficient (a compensate for the large caves at around 700m.
The density and sonic logs suggest a formation change at 690m, but the interval is homogeneous from top ta bottom, being poorly
consolidated clay/shales.
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