Standard Wireline Data Processing
IODP logging
contractor: USIO/LDEO
Hole: U1430B
Expedition:
346
Location: Ulleung Basin (Japan Sea)
Latitude: 37° 54.1670' N
Longitude: 131° 32.2501' E
Logging date:
Sea floor
depth (driller's):
1082.9 m DRF
Sea floor
depth (logger's):
1081.6 m WRF (HRLA/EDTC-B/HNGS tool string)
Total
penetration: 275 m DRF (1357.9 m DSF)
Total core
recovered: 259.71 m (94
% of cored section)
Oldest
sediment recovered:
Miocene
Lithologies:
biosiliceous clay, silty clay, diatom ooze, claystone, sands and tephra
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 September 2013.
| Tool string | Pass
|
Top depth (m WMSF) | Bottom depth (m WMSF) | Pipe depth (m WMSF) | Notes |
1.MSS/HLDS/EDTC-B/HNGS
|
Downlog
|
79 |
Caliper closed. Invalid HLDS. |
||
Repeat
|
open hole |
||||
Main
|
78.5 |
||||
2.HRLA/EDTC-B//HNGS
|
Downlog
|
78.5 |
|||
Repeat
|
open hole
|
||||
Main
|
269 |
78.5 |
Reference run. |
||
3.FMS/DSI/GPIT/HNGS
|
Downlog
|
79 |
Caliper closed. No valid images. |
||
Repeat
|
79 |
||||
Main
|
78.5 |
Hole U1430A was circulated and displaced with mud in preparation for logging. The MSS/HLDS/EDTC/HNGS tool string was lowered without problems to 1160.5 m WRF, where a drop in cable tension occurred and the tool string could not go through. The obstruction was cleared later and the string reached the bottom of the hole. A repeat and main pass were carried out without incidents. The HRLA/EDTC/HNGS tool string was run next. Again, a drop in cable tension occurred at the same depth as in the first run; after pumping, the tool string was able to pass the obstruction and reach the bottom of the hole. A repeat and main pass were conducted without further problems.
The FMS/DSI/GPIT/EDTC/HNGS tool string was run last, with a a pair of 3-arm calipers to centralize the string and the HNGS located at the top, to facilitate comparison wth the first run; overall, the operations were uneventful. The wireline heave compensator was not used, as the ship's heave was less than 0.2 m (peak-to-peak).
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 (-
1081.6 m). The sea floor depth
was determined by the step in gamma ray values at 1081.6 m WRF on the HRLA/EDTC-B/HNGS tool string. This differs by1.3 m from the sea floor depth given by the drillers (1082.9 m DRF). The depth-shifted logs have then been depth-matched to the gamma ray log from the main
run of the HRLA/EDTC-B/HNGS tool string. This pass was chosen as the reference run because it recorded the longest gamma ray curve interval in open hole.
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, HRLA and HLDS data were corrected for hole size during the recording.
High-resolution
data. The bulk density
(HLDS) were recorded with a ampling 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.
Gamma Ray data from the SGT tool were recorded at sampling rates of 5.08 and 15.24
cm.
Acoustic
data. The dipole shear
sonic imager (DSI) was operated in standard frequency P&S monopole, upper and lower dipole, and
Stoneley modes. The data is of accetable quality; however, processing of the sonic waveforms is suggested to improve the quality of the 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
(such as the HLDS). Hole diameter was recorded by the hydraulic caliper on the HLDS
tool (LCAL) and by the FMS tool (C1 and C2). The hole is often in gauge but is enlarged between 150 and 250 m WMSF.
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