Standard Wireline Data
Processing
IODP logging contractor: USIO/LDEO
Hole: U1332A
Expedition: 320
Location:
Equatorial Pacific Sediment Mound (Eastern Equatorial Pacific)
Latitude: 11°
54.711 ' N
Longitude: 141° 02.744 ' W
Logging date: March 24-25, 2009
Sea floor depth (driller's): 4935.1 mbrf
Sea floor depth (logger's):
4935.1 mbrf
Total penetration: 5087.5
mbrf
Total core recovered:
145.61 m (99.1 % of cored section)
Oldest sediment recovered: Middle to late Eocene
Lithologies:
Nannofossil ooze, radiolarian ooze with clay, and 10 cm of basalt at the base
Data
The logging data was recorded by Schlumberger in DLIS
format. Data was processed at the Borehole Research Group of the Lamont-Doherty
Earth Observatory in March 2009.
Logging Runs
|
Tool string |
Pass |
Top depth (mbsf) |
Bottom depth (mbsf) |
Pipe depth (mbsf) |
Notes |
1. MSS/HLDS/HNGS
|
Downlog
|
44.6
|
149.27
|
|
Caliper closed. |
|
2. MSS/HLDS/HNGS |
1 |
75.4 |
151.3
|
|
|
|
3. MSS/HLDS/HNGS |
2 |
64.1
|
149.3
|
76.9 |
Reference |
Logging operations started with the MSS/HLDS/HNGS string,
which recorded data downlog first and then uplog (2 passes). No
problems were encountered during these runs. However, when the tool string was
being retrieved after pass 2, it was lost in hole. As a result, the
FMS/GPIT/HNGS tool string was not run as planned. The caliper was kept open
during the first and second passes, but closed during the downlog.
The WHC was not operated throughout the logging operations
due to malfunction. The sea state was rough, with heave of about 2
meters.
The depths in the table are for the processed logs (after
depth shift to the sea floor and depth matching between passes). Generally,
discrepancies may exist between the sea floor depths determined from the
downhole logs and those determined by the drillers from the pipe length.
Typical reasons for depth discrepancies are ship heave, wireline and pipe
stretch, tides, and the difficulty of getting an accurate sea floor from a
'bottom felt' depth in soft sediment.
Processing
Depth shift to sea floor and depth match. The original logs were first shifted to the sea
floor (- 4935.1 m). The sea floor depth was determined by the driller's depth
(- 4935.1 mbrf), rather than by the step in gamma ray values (logger's depth),
for these logs didn't run through the sea floor. The depth-shifted logs were
then depth-matched to the gamma ray log from pass 2 of the MSS/HLDS/HNGS tool
string. Pass 2 was chosen as the reference because it was the longest among the
three logs.
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 no sudden changes in cable speed),
and then the features in the equivalent logs from the other runs are matched to
it in turn. This matching is performed manually. 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.
Environmental corrections. The HNGS data were corrected for hole size during the recording. The
HLDS data were corrected for standoff and hole size respectively during the
recording.
Magnetic susceptibility data. The magnetic susceptibility tool (MSS) was run for
all three passes. At the time of this processing the recorded data has not been
calibrated yet and therefore is not presented in ASCII file format in the
online database. It will be included at a later date.
High-resolution data.
Bulk density (HLDS) data was recorded at sampling rates of 2.54 cm in addition
to the standard sampling rate of 15.24 cm. 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
The quality of the data is assessed by checking against
reasonable values for the logged lithologies, by repeatability between
different passes of the same tool, and by correspondence between logs affected
by the same formation property (e.g. the resistivity log should show similar
features to the sonic velocity log).
Despite the lack of calibration of the susceptibility log,
there is generally good correlation among the downlog and uplog passes for the
low-resolution susceptibility logs. More processing after calibration is
required to produce final results.
Gamma ray logs recorded through bottom hole assembly (BHA)
and drill pipe should be used only qualitatively, because of the attenuation of
the incoming signal. The thick-walled BHA attenuates the signal more than the
thinner-walled drill pipe.
Hole diameter was recorded by the hydraulic caliper on the
HLDS tool (LCAL). The caliper was kept closed during the downlog and open
during the uplogs. It ranged from 12 to 20", with the higher values recorded above 117 mbsf. A wide
(>12") and/or irregular borehole affects most recordings, particularly
those that require eccentralization and a good contact with the borehole wall
(HLDS). Therefore, log data from the upper portion of the hole and bulk density
data from the downlog (no correction for borehole size) should be used with
caution.
A null value of -999.25 may replace invalid log values.
Additional information about the drilling and logging
operations can be found in the Operations and Downhole Measurements sections of
the expedition reports, Proceedings of the Integrated Drilling Program,
Expedition 320. For further questions about the logs, please contact:
Tanzhuo Liu
Phone: 845-365-8630
Fax: 845-365-3182
E-mail: Tanzhuo Liu
Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia