Standard Wireline Data Processing
IODP logging
contractor: USIO/LDEO
Hole: U1423B
Expedition:
346
Location: Japan Basin (Japan Sea)
Latitude: 41° 41.9575' N
Longitude: 139° 4.98' E
Logging date:
Sea floor
depth (driller's):
1796.8 m DRF
Sea floor
depth (logger's):
1795.2 m WRF (FMS/DSI/GPIT/EDTC-B Main Run)
Total
penetration: 2045.9 m DRF (249.1 m DSF)
Total core
recovered: 249.1 m (100%)
Oldest
sediment recovered:
Lower Pliocene
Lithologies: Biosiliceous clay, silty clay and ash layers
The logging data
was recorded by Schlumberger in DLIS format. Data were processed at the
Borehole Research Group of the Lamont-Doherty Earth Observatory in August 2013.
| Tool string | Run
|
Top depth (m WMSF) | Bottom depth (m WMSF) | Pipe depth (m WMSF) | Notes |
1. HRLA/MSS/HLDS/EDTC-B/HNGS
|
Downlog
|
80 |
|
||
Repeat
|
recorded open hole |
||||
Main
|
80 |
||||
2. FMS/DSI/GPIT/EDTC-B
|
Downlog
|
80 |
Closed caliper; invalid FMS |
||
Repeat
|
recorded open hole |
||||
Main
|
80 |
Depth reference |
The logging operations at Hole U1423B were uneventful. Since no problems were encountered during drilling, the preparations for logging consisted of bottom circulation only. The Wireline Heave Compensator (WHC) was not used due to the calm sea conditions (peak-to-peak heave less than 0.2 m).
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.
Depth shift to sea floor and depth match. The original logs were first shifted to the sea floor (-1795.2m). The sea floor depth was determined by the step in gamma ray values at 1795.2 m WRF. This differs by 1.6 m from the sea floor depth given by the drillers (1796.8 m DRF). The depth-shifted logs have then been depth-matched to the gamma ray log from the main run of the FMS/DSI/GPIT/EDTC-B tool string.
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 and mud weight during the recording.The EDTC-B
and HLDS data were corrected for hole size during the
recording.
High-resolution
data. The bulk density
(HLDS) data were recorded with a sampling rate 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.
The gamma Ray data from the EDTC-B tool were recorded at sampling rates of 5.08 and 15.24
cm.
Acoustic
data. The dipole shear
sonic imager (DSI) was operated in the following modes: P&S monopole, upper and lower dipoles, and
Stoneley on all three runs with standard frequency except for the lower dipole mode in the repeat log. The lower dipole recording from the repeat log was originally carried out in low frequency hoping to acquire better data in the soft formation, but it did not compare favorably with the standard frequency data acquired on the way down. Therefore the lower dipole was switched back to standard frequency for the main log. Sonic waweform processing is recommended to obtain improved results.
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).
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.
A wide
(>12") and/or irregular borehole affects most recordings, particularly
those that require eccentralization and a good contact with the borehole wall
(HLDS). Hole diameter was recorded by the hydraulic caliper on the HLDS
tool (LCAL) and by the FMS tool (C1 and C2). The caliper data are in gauge, thus confirming that the hole was in very good conditions for recording.
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 346.
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