Standard Wireline Data Processing
Science operator: Texas A&M University
Hole: U1514C
Expedition: 369
Location: Mentelle Basin (SE Indian Ocean)
Latitude: 33° 7.2443' S
Longitude: 113° 5.4799' E
Logging date: November 9, 2017
Sea floor
depth (driller's): 3850 m DRF
Sea floor depth (logger's): 3845.7 m WRF
Total
penetration: 4366.8 m DRF (516.8 m DSF)
Total core
recovered: 247.47 m (77 %)
Oldest sediment recovered: Cenomanian
Lithologies: clayey nannofossil chalk, nannofossil-rich claystone, claystone
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 November 2017.
| Tool string | Pass
|
Top depth (m WMSF) | Bottom depth (m WMSF) | Pipe depth (m WMSF)
|
Notes |
1. MSS/HRLA/DSI/HLDS/EDTC-B/HNGS
|
Down
|
Caliper closed. Invalid HLDS.
|
|||
Repeat
|
|
||||
Main
|
Depth reference
|
Drilling at hole U1514C did not encounter any problem, therefore a stable hole was expected for the logging operations. Prior to logging a sepiolite-seawater mud (10.5 lb/gal) was added to the hole. Like in the previous two holes, a modified logging string was employed, which included the sonic (DSI) tool in place of the porosity (APS) tool. The magnetic susceptibility tool (MSS) was added at the bottom, below the gamma ray spectrometry (HNGS) tool.
The average heave ranged from 0.5 to 1.5 m with occasional peaks of 3 m during logging. The motion heave compensator was used whenever the tools were in open hole.
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 match and depth shift to sea floor. The original logs were first depth-matched to the gamma ray log from the main pass of the MSS/HRLA/DSI/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.
The depth-matched logs were then shifted to the sea floor.
Environmental corrections. The HNGS, HRLA, and HLDS uplog data were corrected for hole size using the caliper readings during the recording, while the downlog data were corrected utilizing the bit size.
High-resolution
data. Bulk density
(HLDS) data were 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 are 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 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 and upper and lower dipole during all 3 passes. The sonic velocities were computed from the delay times. They are
generally of very good quality, however, reprocessing of the sonic waveforms is recommended post cruise to get even more accurate 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).
All three passes showed good repeatability. The resistivity (HRLA) data locally show some short straight-line intervals, possibly caused by stick-and-slip and heave, which are not compensated for by the motion heave compensator.
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). The caliper shows a very smooth hole ranging from 10 to14 inches in diameter. In most of the logged interval, however, the hole diameter ranges between 10 and 12 inches.
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 report, Proceedings of the International Ocean Discovery Program, Expedition 369. For further questions about the logs, if the hole is still under moratorium please contact the staff scientist of the expedition.
After the moratorium period you may direct your questions to:
Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia
Tanzhuo Liu
Phone: 845-365-8630
Fax: 845-365-3182
E-mail: Tanzhuo Liu