Standard Wireline Data Processing
Science operator: Texas A&M University
Hole: U1513A
Expedition: 369
Location: Mentelle Basin (SE Indian Ocean)
Latitude: 33° 47.6084' S
Longitude: 112° 29.1338' E
Logging date: October 23, 2017
Sea floor depth (driller's): 2800.2 m DRF
Sea floor depth (logger's): 2801.2 m WRF
Total penetration: 3092.7 m DRF 292.5 (m DSF)
Total core recovered: 170.6 m ( 58 % of cored section)
Oldest sediment recovered:
Lithology: calcareous ooze, nannofossil ooze with chert, nannofossil chalk, silicified limestone, and clayey nannofossil chalk.
The logging data
were recorded by Schlumberger in DLIS format. Data were processed at the
Borehole Research Group of Lamont-Doherty Earth Observatory in October 2017.
| Tool string | Pass
|
Top depth (m WMSF) | Bottom depth (m WMSF) | Pipe depth (m WMSF) | Notes |
1. HRLA/DSI/HLDS/EDTC-B/HNGS
|
Downlog
|
~81.2 |
|
||
Repeat
|
Recorded open hole |
||||
Main
|
~77.8 |
Reference depth |
The drilling and coring operations at Hole U1513A proceeded without incidents. Prior to logging, the hole was conditioned with sepiolite-seawater (10 lb/gal) mud. Like in the previous hole, the tool string was modified by removing the porosity (APS) tool and replacing it with the sonic (DSI) tool and by moving the gamma ray tool (HNGS) to the bottom in order to get a full signature in the lower part of the hole. The downlog recording was carried out with the caliper closed and proceeded without problems. A repeat pass followed with the caliper open. The main pass, also carried out with the caliper open, experienced some tension over pulls while getting into the drill pipe, which resulted in the gamma ray (HNGS) and density (HLDS) tools detecting the drill pipe at different depths (2879 and 2882 m WRF respectively). The FMS and VSI logs were cancelled due to time constraints.
The average heave was about 1 m with occasional values of 2 m just prior to 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 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 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, HLDS, and HRLA data were corrected for hole size during the recording.
High-resolution
data. The bulk density
(HLDS) data were recorded at 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 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 in all three passses. The sonic velocities were computed from the 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
(HLDS). Hole diameter was recorded by the hydraulic caliper on the HLDS
tool (LCAL). When open, the caliper varied from 12 to 16 in, with some locally higher values.
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