Wireline Standard Data Processing
ODP logging contractor: LDEO-BRG
Hole: 1165C
Leg: 188
Location: Prydz Bay (Antarctic Ocean)
Latitude: 64° 22.8' S
Longitude: 67° 13.1' E
Logging date: February 13-14, 2000
Bottom felt: 3548.7 mbrf
Total penetration: 999.1 mbsf
Total core recovered: 69.3%
Logging
Runs
Logging string 1: DIT/APS/HLDS/HNGS + TAP
tool
Logging string 2: FMS/GPIT/DSI/NGT (1 main
and 2 repeat passes)
After several drilling interruptions due to
the approach of icebergs, Hole 1165C was prepared for logging. On the first
attempt, the DIT/APS/HLDS/HNGS tool string could not penetrate more than 50 m
into the open hole; on a second attempt, after lowering the pipe to 175 mbsf,
the DIT/APS/HLDS/HNGS reached total depth. The logs were of very good quality,
except in the vicinity of a bridge at around 310 mbsf. The FMS/GPIT/NGT tool
string reached about 590 mbsf, then the vertical axis accelerometer on the GPIT
tool failed, followed by a complete communications loss to the FMS tool. FMS
tool problems were also encountered during the recording of two repeat runs.
Only DSI and NGT data are valid.
The Wireline Heave Compensator was used to
counter ship heave.
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, drill string and/or wireline
stretch, and tides.
DIT/APS/HLDS/HNGS: Bottom-hole assembly at
175 mbsf
FMS/GPIT/DSI/NGT: Bottom-hole assembly at 175
mbsf.
Processing
Depth shift: The original logs were depth matched to the HNGS from
the DIT/APS/HLDS/HNGS run and were then shifted to the sea floor (-3546.5 m).
The sea floor depth is determined by the step in gamma ray values at the
sediment-water interface. This depth differs by 2.2 m from the driller’s
sea-floor depth, which was determined by the mudline in the hole 1165A.
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.
The depth match between the different passes
of the tool strings at 1165C is generally robust, except where the
DIT/APS/HLDS/HNGS tool string became trapped for a short time under a bridge at
about 310 mbsf.
Gamma-ray processing: NGT data from the FMS/GPIT/DSI/NGT run have been
processed to correct for borehole size. The HNGS data from DIT/HLDS/APS/HNGS
was corrected for hole size during the recording. The HNGS data are
statistically better than the NGT data. While total gamma ray counts (HSGR and
SGR) are reproducible and show very similar features, the potassium, thorium,
and uranium logs are less robust, due to the statistical nature of the gamma
ray measurement.
Acoustic data processing: The DSI tool was operated in P&S and lower dipole
modes. The waveform data from were processed during logging to give DTCO
(compressional wave slowness), and DTSM (shear wave slowness). While the DTSM
appears to be good data (corresponds to features observed in the resistivity
logs), much of the DTCO has values are too high (velocities are too low). Since
trying to correct for this would involve making up data (subjectively), the
original data are given in the data files. 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.
Quality
Control
Null value=-999.25. This value may replace
invalid log values or results.
Large (>12") and/or irregular
borehole affects most recordings, particularly those that require
eccentralization (APS, HLDS) and a good contact with the borehole wall. In
general, Hole 1165C was moderately smooth, varying between 13-15 inches in
diameter below 550 mbsf, and between 14-18 inches above 550 mbsf. APS and HLDS
data quality is reduced in the rough and/or wide intervals. Hole diameter was recorded
by the hydraulic caliper on the HLDS tool (LCAL) and on the FMS string (C1 and
C2) (repeat passes 1 and 2 only).
Additional information about the logs can be
found in the "Explanatory Notes" and Site Chapter, ODP IR volume 188.
For further questions about the logs, please contact:
Cristina Broglia
phone: 845-365-8343
fax: 845-365-3182
email: Cristina Broglia