ODP logging contractor: LDEO-BRG
Hole: 1140A
Leg: 183
Location: Kerguelen Plateau
(Antarctic Ocean)
Latitude: 46° 16.599' S
Longitude: 68° 29. 4984' E
Logging date: January, 1999
Bottom felt: 2406 mbrf
Total penetration: 321.9 mbsf
Total core recovered: 144.9 m (45
%)
Logging
Runs
Logging string 1: DIT/APS/HLDS/HNGS
Logging string 2: FMS/GPIT/SDT/NGT
Logging string 3: WST
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, use of wireline heave
compensator, and drill string and/or wireline stretch.
DIT/APS/HLDS/HNGS: Bottom-hole assembly at ~ 80 mbsf
FMS/GPIT/SDT/NGT: Recorded open hole.
Processing
Depth shift: Because of an invalid HNGS on the DIT/APS/HLDS/HNGS
tool string, the logs have been interactively depth shifted with reference to
the caliper from DIT/APS/HLDS/HNGS run and to the sea floor (- 2408 m). This
value takes in account the 2-m offset observed at the bottom of the pipe at
2488 mbrf (the drillers originally indicated the pipe bottom at 2486 mbrf). The
program used is an interactive, graphical depth-match program, which allows to
visually correlate logs and to define appropriate shifts. The reference and
match channels are displayed on the screen, with vectors connecting old
(reference curve) and new (match curve) shift depths. The total gamma ray curve
(SGR) from the NGT tool run on each logging string is used to correlate the
logging runs most often. In general, the reference curve is chosen on the basis
of constant, low cable tension and high cable speed (tools run at faster speeds
are less likely to stick and are less susceptible to data degradation caused by
ship heave). Other factors, however, such as the length of the logged interval,
the presence of drill pipe, and the statistical quality of the collected data
(better statistics is obtained at lower logging speeds) are also considered in
the selection. A list of the amount of differential depth shifts applied at
this hole is available upon request.
Gamma-ray processing: NGT data
from the FMS/GPIT/SDT/NGT runs have been processed to correct for borehole size
and type of drilling fluid. The HNGS tool did not function properly at this
hole, therefore the data is invalid.
Acoustic data processing: The SDT tool, operated in depth-derived, borehole compensated long spacing sonic mode (8-10-10-12 ft), recorded good data in the sedimentary section, while
the basement section was affected by frequent cycle skipping. Therefore, the
logs have been processed to eliminate some of the noise and cycle skipping
experienced during the recording. Using two sets of the four transit time
measurements and proper depth justification, four independent measurements over
a -2ft interval centered on the depth of interest are determined, each based on
the difference between a pair of transmitters and receivers. The program
discards any transit time that is negative or falls outside a range of
meaningful values selected by the processor.
High-resolution data: Neutron
porosity data were recorded at a sampling rate of 5.08 cm.
Quality
Control
null value=-999.25. This value may replace
invalid log values or results.
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. Hole
deviation can also affect the data negatively; the FMS, for example, is not
designed to be run in holes deviated more than 10 degrees, as the tool weight
might cause the caliper to close. Hole deviation at this hole was about 5
degrees.
Hole diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL) and
on the FMS string (C1 and C2).
Some logging data from the upper and lower section of the hole were merged as
follows:
- FMS caliper merged at 240 mbsf
- Acoustic data merged at 220 mbsf
- Gamma Ray data merged at 215 mbsf
Additional information about the logs can be found in the "Explanatory
Notes" and Site Chapter, ODP IR volume 183. For further questions about
the logs, please contact:
Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia