Standard Wireline Data Processing
IODP logging contractor: USIO/LDEO
Hole: U1437D
Expedition: 350
Location: Izu-Bonin-Mariana Rear Arc (Philippine Sea)
Latitude: 31° 47.3874' N
Longitude: 139° 01.5723' E
Logging date: April 21-23, 2014
Sea floor depth (driller’s): 2127.3 m DRF
Sea floor depth (logger's): 2126.5 m WRF (MSS/HRLA/APS/HLDS/EDTC-B/HNGS Main Run)
Total penetration (RCB coring): 3107.7 m DRF (980.4 m DSF) .
Total core recovered: 78 m (78% of cored interval); upper 440 m cored in hole B (55% recovery)
Oldest sediment recovered: 6 Ma, Upper Miocene (from paleomagnetic measurements; all microfossils recovered are too reworked for proper biostratigraphic identification.)
Lithology: Mud with dispersed ash, intercalated intervals of mafic and evolved ash, tuff, tuffaceous mudstone
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 April 2014.
| Tool string | Pass
|
Top depth (m WMSF) | Bottom depth (m WMSF) | Pipe depth (m WMSF) | Notes |
1. MSS/HRLA/APS/HLDS/EDTC-B/HNGS
|
Downlog
|
92 |
Caliper closed. Invalid APS and HLDS |
||
Main
|
92 |
Depth reference |
|||
Repeat
|
open hole |
||||
2. FMS/DSI/GPIT/EDTC-B/HNGS
|
Downlog
|
92 |
Calipers closed. Invalid FMS |
||
Main
|
open hole |
||||
Repeat
|
open hole |
||||
3. VSI/EDTC-B |
Pass 2
|
92 |
14 stations |
Drilling and coring were carried out without any problems down to 3107.7 m DRF (980.4 m DSF), at which point a change of bit was deemed necessary. It was then decided to start logging the drilled interval and resume coring to the target depth of about 3227 m DRF (1100 m DSF) later. Hole conditions were very good. Only minimal conditioning was necessary in preparation for logging: 50 bbl of sepiolite-based mud was used at the very bottom before pulling out of the hole and dropping the bit to the sea floor.
The MSS/HRLA/APS/HLDS/EDTC-B/HNGS tool string was run first and reached the depth of 3091 m WRF, 16.7 m above the total depth, indicating the presence of soft in-fill at the bottom of the hole. A downlog, repeat and main passes were acquired.
The FMS/DSI/GPIT/EDTC-B/HNGS tool string was lowered next, which acquired a downlog (gamma ray data and sonic data only) and main and repeat passes. The recording of the DSI data during the main pass was interrupted by mistake when the FMS arms were closed at 2260 m WRF before entering the drill pipe. However, good DSI data in the missed interval of the main pass were acquired during the downlog.
The vertical seismic log (VSI) took place after an hour survey for sea life. The VSI was stopped at 2800 m WRF for a short gamma ray recording to tie the depth to the GR log of the MSS/HRLA/APS/HLDS/EDTC-B/HNGS tool string. The tool string reached a depth of 3025 m WRF and succeesfully acquired 14 stations every 50 m from 3000 m WRF to 2350 m WRF.
Drilling and coring resumed after logging collecting an additional 14 cores, but hole conditions became hazardous and it was decided to case the hole to a depth of 3217.3 m DRF (1090 m DSF) and not to log the lower part of the hole.
The sea state was low with a peak-to-peak heave of ~ 0.1-0.3 m . The wireline heave compensator was not used during the logging operation.
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 for the following amounts:
-2126.5 m (MSS/HRLA/APS/HLDS/EDTC-B/HNGS Downlog)
-2125.5 m (MSS/HRLA/APS/HLDS/EDTC-B/HNGS Main and Repeat Runs)
-2123.5 m (FMS/DSI/GPIT/EDTC-B/HNGS Downlog)
-2122.9 m (FMS/DSI/GPIT/EDTC-B/HNGS Main Run)
-2122.7 m (FMS/DSI/GPIT/EDTC-B/HNGS Repeat Run)
The sea floor depth was determined by the step observed at the mudline in the gamma ray value. This differs as much as 4.6 m from the sea floor depth given by the drillers (see above). The depth-shifted logs have then been depth-matched to the gamma ray log from the main run of the MSS/HRLA/APS/HLDS/EDTC-B/HNGS 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
and HRLA data were corrected for hole size during the recording. The APS and
HLDS data were corrected for standoff and hole size respectively during the
recording.
High-resolution data. Bulk density (HLDS) and neutron porosity (APS) data were recorded sampling rates of 2.54 and 5.08 cm, respectively, 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 are smoothed to match the long-spacing ones, 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.
Acoustic
data. The dipole shear
sonic imager (DSI) was operated in the following modes: P&S monopole, upper and lower dipole, and
Stoneley during all passes. The standard frequency was used for all modes except for the lower dipole mode, where the lower frequency was used. The sonic velocities were computed from time slownesses after they were corrected on board by Schlumberger to improve their quality. The sonic velocity data are
generally of very good quality.
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 features similar 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 (APS, HLDS). Hole diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL) and by the FMS tool (C1 and C2). This hole was in very good conditions.
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 350.
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