Wireline Standard Data Processing
ODP logging contractor: LDEO-BRG
Hole: 1172D
Leg: 189
Location: East Tasman Plateau (Tasman
Sea)
Latitude: 43° 57.5545' S
Longitude: 149° 55.7169' E
Logging date: 2-3 May 2000
Bottom felt: 2633 mbrf (used for
depth shift to sea floor)
Total penetration: 766.5 mbsf
Total core recovered: 237.09 m (79.6
%)
Logging
Runs
Logging string 1: DIT/APS/HLDS/HNGS
Logging string 2: GHMT/DSI/NGT (main and repeat passes)
Hole 1172D was logged under conditions of
high ship heave, which meant that the wireline heave compensator (WHC) stopped
repeatedly during the first run, and was not used for most of the second.
Despite this, the data are of good quality. Heave was too high to run the FMS
tool string, as planned.
Bottom-hole
Assembly
The following bottom-hole assembly depths are
as they appear on the logs after differential depth shift (see "Depth
shift" section) and depth shift to the sea floor. As such, there might be
a discrepancy with the original depths given by the drillers onboard. Possible
reasons for depth discrepancies are ship heave, malfunction of the wireline
heave compensator, and drill string and/or wireline stretch.
DIT/APS/HLDS/HNGS: Bottom-hole assembly at
150 mbsf
GHMT/NGT/DSI: Bottom-hole assembly at 164
mbsf (main pass)
Processing
Depth shift: The original logs were depth matched to the NGT from
the GHMT/NGT/DSI run and were then shifted to the sea floor (-2633 m). The sea
floor depth is determined by the step in gamma ray values at the sediment-water
interface. In this case it is the same as the "bottom felt" depth
given by the drillers (see above).
Depth matching is typically done in the
following way. One log is chosen as reference (base) log (usually the total
gamma ray log from the run with the greatest vertical extent), and then the
features in the equivalent logs from the other runs are matched to it in turn.
This matching is performed automatically, and the result checked and adjusted
as necessary. The depth adjustments that were required to bring the match log
in line with the base log are then applied to all the other logs from the same
tool string.
For Hole 1172D, the SGR log from the
GHMT/DSI/NGT main run was used as the reference log for two reasons: first,
because the head tension (DF) log seemed less erratic than the DF log from the
DIT/APS/HLDS/HNGS run. Second, because when the Wireline Heave Compensator
stops, as it did often during the DIT/APS/HLDS/HNGS run, it stops at either end
of its track, and has to be reset to the middle of the track to start up again.
The resulting depth errors can be on the order of 3 m
Due to the WHC repeatedly stopping during the
DIT/APS/HLDS/HNGS run, there are offsets between some logs, for example between
the acoustic data and the resistivity logs at 350 mbsf, a depth where the gamma
ray logs match well. The Wireline Heave Compensator stopped between 331-350,
355-439, 624-645, and 662-706 mbsf on the DIT/APS/HLDS/HNGS run.
Gamma-ray processing: NGT data have been processed to correct for borehole
size and type of drilling fluid. The HNGS data were corrected for hole size
during the recording.
Acoustic data processing: The DSI waveform data were processed during logging to
give DTCO (compressional wave slowness) and DTSM (shear wave slowness). The
DTCO from the main pass looks reasonable and matches well to the 100 m of the
repeat pass. The DTSM appears to have some unreasonable values in the 490-493,
450-465, and 560-615 mbsf intervals. No editing was performed, and the
compressional and shear slownesses were then converted to velocities.
High-resolution data: Bulk density and neutron porosity data were recorded
at a sampling rate of 2.54 and 5.08 cm respectively. The enhanced bulk density
curve is the result of Schlumberger enhanced processing technique performed on
the MAXIS system onboard. While in normal processing short-spacing data is
smoothed to match the long-spacing one, in enhanced processing this is
reversed. In a situation where there is good contact between the HLDS pad and
the borehole wall (low density correction) the results are improved, because the
short-spacing has better vertical resolution.
Geological Magnetic Tool: The Geological Magnetic Tool collected data at two
different sampling rates, the standard 0.1524 m rate and 0.0508 m. A handful of
anomalous spikes are present in the magnetic field (MAGB) log, but the data
appear reliable. Both data sets have been depth shifted to the reference run
and to the sea floor.
Quality
Control
null value=-999.25. This may replace recorded
log values or results, which are considered invalid.
During the processing, quality control of the
data is mainly performed by cross-correlation of all logging data. Large
(>12") and/or irregular borehole affects most recordings, particularly
those that require eccentralization (APS, HLDS) and a good contact with the
borehole wall. From 168-412 mbsf, Hole 1172D was between 11 and 13 inches wide
with a few washouts, from 412-505 mbsf the hole had a widely varying diameter,
to 19 inches, and below 505 mbsf, the hole was a little rugose, but mostly
between 10 and 13 inches wide.
Data recorded through bottom-hole assembly,
such as the gamma ray data, should be used qualitatively only because of the
attenuation on the incoming signal.
Hole diameter was recorded by the hydraulic
caliper on the HLDS tool (LCAL).
Details of standard shore-based processing
procedures are found in the "Explanatory Notes" chapter, ODP IR
Volume 189. For further information about the logs, please contact:
Trevor Williams
Phone: 845-365-8626
Fax: 845-365-3182
E-mail: Trevor Williams
Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia