ODP logging contractor: LDEO-BRG
Well name: 831B
Leg: 134
Location: Bougainville Guyot (tropical SW Pacific)
Latitude: 16° 00.56' S
Longitude: 166° 40.36' E
Logging date: November, 1990
Bottom felt: 1077.6 mbrf (used for depth shift to sea floor)
Total penetration: 852 mbsf
Total core recovered: 87.3 m (11.6 %)
Logging
Runs
Logging string 1: DIT/SDT/HLDT/NGT
Logging string 2: ACT/GST/NGT
Logging string 3: FMS/GPIT/NGT
(upper, lower, and middle sections). Note: a repeat run was recorded but it was
not included at the time of processing).
Logging string 4: NMRT/SUMBT
Logging string 5: BHTV
No
information available from logging reports about use of wireline heave
compensate 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
and drill string and/or wireline stretch.
DIT/SDT/HLDT/NGT:
Bottom-hole assembly at ~84 mbsf
ACT/GST/NGT:
Bottom-hole assembly at ~84 mbsf
FMS/GPIT/NGT:
Bottom-hole assembly at ~84 mbsf.
Processing
Depth
shift: Original logs have been
interactively depth shifted with reference to NGT from DIT/SDT/HLDT/NGT run and
to the sea floor (- 1077.6 m). 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 have been processed
to correct for borehole size and type of drilling fluid.
Acoustic
data processing: The array sonic tool was
operated in standard depth-derived borehole compensated mode, including
long-spacing (8-10-10-12') logs. The sonic logs are of too poor of a quality to
be processed. Some correlation with the resistivity logs is observed only in
the 412-590 and 600-800 mbsf intervals.
Quality
Control
null
value=-999.25. This value generally appears in discrete core measurement files
and also it 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 (HLDT) 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.
Data
recorded through bottom-hole assembly should be used qualitatively only because
of the attenuation on the incoming signal.
Hole
diameter was recorded by the hydraulic caliper on the HLDT tool (CALI) and on
the FMS string (C1 and C2).
Additional
information about the logs can be found in the "Explanatory Notes" and Site
Chapter, ODP IR volume 134. For further questions about the logs, please
contact:
Cristina
Broglia
Phone:
845-365-8343
Fax:
845-365-3182
E-mail:
Cristina Broglia
Trevor
Williams
Phone:
845-365-8626
Fax:
845-365-3182
E-mail:
Trevor Williams