Standard Wireline Data Processing
Science operator: Texas A&M University
Hole: U1482C
Expedition: 363
Location: Scott Plateau (tropical SE Indian Ocean)
Latitude: 15° 3.3298' S
Longitude: 120° 26.1135' E
Logging date: October 24, 2016
Sea floor depth (driller's): 1476.1 m DRF
Sea floor depth (logger's): 1476.5 m WRF (MSS/HRLA/APS/HLDS/EDTC/HNGS downlog)
Total penetration: 2010.6 m DRF (534.5 m DSF)
Total core recovered: 536.34 m (103.7% of cored section)
Oldest sediment recovered: 10 My
Lithology: nannofossil and foraminiferal ooze, chalk
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 October 2016.
| Tool string | Pass
|
Top depth (m WMSF) | Bottom depth (m WMSF) | Pipe depth (m WMSF) | Notes |
1.MSS/HRLA/APS/HLDS/EDTC/HNGS
|
Downlog
|
83.5 |
Caliper closed and APS minitron off. Invalid APS and HLDS. Depth reference |
||
Repeat
|
open hole |
||||
Main
|
83.5 |
||||
2.FMS/DSI/GPIT/EDTC/HNGS
|
Downlog
|
76.5 |
Caliper closed. Invalid FMS. |
||
Pass 1
|
open hole |
||||
Pass 2
|
76.5 |
In preparation for logging, the pipe was lowered to about 83.5 m DRF and the hole was pumped with seawater.
The MSS/HRLA/APS/HLDS/EDTC/HNGS tool string was run first, with the APS minitron turned off during the downlog. A short repeat pass was recorded, followed by the main pass from total depth to the sea floor. No major problems were encountered during the recording. However, re-entering the drill pipe proved to be difficult as the logging string head would not pass easily through the lockable float valve. After pumping seawater and rotating the pipe the logging string was eventually able to pass throgh without any damage. The difficulty was possibly due to the presence of dense clay coating the tools and the tool head, especially the centralizers, which was observed once the tool string reached the sea floor.
The FMS/DSI/GPIT/EDTC/HNGS tool string was run next. Prior to the recording, the drill pipe was raised to about 76.5 m DRF in order to maximize the amount of FMS data collected in open hole. A downlog (with caliper closed) and two uplog passes were recorded. Again, getting into the pipe proved to be difficult but eventually the tool string made it to the surface without any damage.
Since the sea conditions were calm (peak-to-peak heave of <0.5 m), the wireline heave compensator was not used during the logging operations. However, a 4m tide was expected at the site and could affect the log depths since it cannot be eliminated during the data acquistion process.
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 (- 1476.5 m). The sea floor depth was determined by the step in gamma ray values at - 1476.5 observed on the downlog of the MSS/HRLA/APS/HLDS/EDTC/HNGS run. This differs by 0.4 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 downlog of the MSS/HRLA/APS/HLDS/EDTC/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 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 the following modes: P&S monopole
and upper and lower dipole (run/pass) in all three passes. The velocities were computed from the DTCO (compressional monopole), and DT1/DT2 (shear lower and upper dipole) delay times. They are
generally of 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 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 (APS, HLDS). Hole diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL) and by the FMS tool (C1 and C2). The hole diamteter was mostly between 12 and 16 inches, with higher values in the presence of washouts, and less than 12 inches in the lower third of the hole.
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 363. 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