Page 183 - The Geological Interpretation of Well Logs

~ THE DIPMETER -

which then define a surface across the hole. There are are only for detailed work.
two principal methods: fixed interval correlation and It is essential to understand the general principles of
feature recognition. Fixed interval correlation is the most dipmeter processing; proper interpretation depends on it.
common method used and simplest for the computer but This will be demonstrated subsequently, It is not neces-
feature recognition imitates the way the human eye sary to know the details of the computer programmes,
works. Processing is normally done automatically by the which vary between companies, but the basic, consistent-
computer, but a modern development is the possibility of ly used principles must be understood. The essentials of
correlating the curves and producing dips interactively on the two methods (fixed interval and feature recognition)
the computer screen (Figure 12.7). Interactive methods will be described separately below.

Gamma Ray (API) matres PAD 1 PAD 2 AD 3 PAD 4
oo
TENSION {LBS) X-CALIPER (INCH)
DEV (DEG)
Y-CALIPER (INCH)
AZ (DEG)

Figure 12.6 Standard log presentation of raw dipmeter data, The dipmeter curves are sampled every 0.5cm (0.2”) while the
standard logs are sampled every 15cm (6"} (Western Atlas Diplog). DEV = hole deviation from the vertical. DAZ = azimuth of
hole deviation. AZ = azimuth of pad }. Pad 1-4 = pad conductivity curves.
Resistivity a> Resistivity mi» Resistivity => o 20° 40° Dip 30°

9 T
curve 3
curva 1 ! curve 2
a ae { ; ae

!
FIXED
INTERVAL = INTERVAL
es
CORRELATION J CORRELATION
im Ve oe
OIP
1
I

CORRELOGRAM
curve 1
correlogram
transposed
for interval
correlation

MY
NSF
o 90°
2m 4

D.[ FEATURE ‘
POINT
RECOGNITION
{ CORRELATION
DIP
CORRELATION !
correlation
1 line
depth { 1

Figure 12.7 Correlation methods for deriving dip and azimuth from dipmeter resistivity curves. a) Fixed interval correlation: one
dip is produced representing the entire selected interval; b) feature recognition correlation: a dip is produced representing the
correlation of a recognizable feature. Fixed interval correlation methods are the most common: feature recognition imitates the
way the eye correlates. Example taken from interactive screen routines in QLOG.
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