Page 203 - The Geological Interpretation of Well Logs

- THE DIPMETER -

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1609 ee
ee pe f i “ Li} jee
5 dy
1708
wo
1900 ie
& 4
~
“ :
AHZOOBMDIDO *k, ° Figure 12.34 A slight angular unconfor-
2188 2 Ss g a
‘* ‘.
mity indicated by zoned dipmeter data.
ACOA Only when the unconformity is picked
2
iy
on the standard logs and the dipmeter
. ~ Ei “as. data are zoned, do the differences in
2900 | - azimuth become apparent. This type of
y od |
unconformity is typica}.
Faults Interpreters often confuse the two, but the scale is quite
Faults are identified on the dipmeter through geometncal different as illustrated below.
distortion: that is changes of dip or changes of azimuth, A second confusion is that the dipmeter can seldom give
or both (Figure 12.30). If there is no distortion, no fault a conclusive indication of fault plane dip, or of whether the
will be seen. In reality, there are two types of distortion fault is normal or reversed. If distortion about a fault is
with a potential to be identified on the dipmeter: distor- cylindrical, a fault plane strike can be given but not the dip
tion about the fault plane itself and distortion, or of the fault plane. The following examples show this.
geometrical change from one fault block to another.

STICK cr —>
Ww EW EO 20* aor oy

A. — STEREOGRAM
DRAG w — te
—
— +
— Je
—— 7%
—- |-
=| {tb
7
%
<— eh
oat “7 Ho
1 | x lL. Le falsit
— -
— |
—7

— +
— 7
—
b—
— 7
— 7
A DIP —>
w E wi sO OF 20 49' 30’

B. a
ROLLOVER S45
REVEASE DRAG — |e
— eq
J \=|* o
—_
— -
—, -
— -
=
a
100m| aw
. L —_— 4 1 ®| -_ L
=
»
=
”
— + faut
—_— +

—F

— 44
—_— +
Figure 12.35 Fault characteristics on the dipmeter illustrated by a sketch, log and stereogram (Schmidt). A. drag, typically ata
small scale around the fault plane itself. The stereogram shows cylindrical distortion with the highest dip close to the dip and
orientation of the fault plane. B. rollover or reverse drag, a large scale effect. The stereogram shows cylindrical distortion with the
dip of the fault plane opposite to bedding dip.
193