Standard Wireline Data Processing
Science operator: Texas A&M University
Hole: U1579D
Expedition: 392
Location: Agulhas Plateau (SW Indian Ocean)
Latitude: 39° 57.0725' S
Longitude: 26° 14.1793' E
Logging date: February 24, 2022
Sea floor depth (driller's): 2504.0 m DRF
Sea floor depth (logger's): 2504.0 m WRF
Total penetration: 3231.2 m DRF (727.2 m DSF)
Total core recovered: 440.84 m (73.8 % of cored section)
Oldest sediment recovered:
Lithology: Calcareous sediments, zeolitic siliciclastic sediments and basalt
The logging data were recorded by Schlumberger in DLIS format. Data were processed at the Borehole Research Group of Lamont-Doherty Earth Observatory in March, 2022.
| Tool string | Pass
|
Top depth (m WMSF) | Bottom depth (m WMSF) | Pipe depth (m WMSF) | Notes |
MSS/HRLA/DSI/HLDS/HNGS
|
|
67 |
Caliper closed. Invalid HLDS. Reference run for depth matching. |
||
|
|
Recorded open hole |
||||
67 |
After the completion of coring operations, the MSS/HRLA/DSI/HLDS/HNGS tool string was deployed for logging. Two downlogs were run with the caliper closed and the HLDS radioactive source turned off. A short high-resolution repeat pass (with the logging speed of 900 ft/hr) and a main pass (with the logging speed of 1800 ft/hr) followed (each with the radioactive source turned on), the latter from total depth to the sea floor. A splice file of the two downlogs was used for data processing.
The Wireline Heave Compensator (WHC) was used in the open hole intervals to counter the ship heave while logging.
The depths in
the table are for the processed logs (after depth matching between passes and depth shift to the sea floor). 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 the 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 downlog pass of the MSS/HRLA/DSI/HLDS/HNGS tool string. The downlog was chosen as the reference run because it showed the sea floor at the same depth as the drillers'. 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 HRLA and HLDS logs were corrected for hole size during the recording.
High-resolution
data. 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, upper and lower dipole. The sonic velocities were computed from the slownesses data.
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.
The DSI labeling corrections were made by the Schlumberger engineer for the final downlog splice file; the real time processing did not correctly label the signals. The sonic velocities generally correlate well with the resistivity logs.
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. For U1579D, the caliper was near bit size of 9 7/8" for most of the logged hole interval with variations reaching up to 12"; it did extend to 17" at 120 m WMSF and above. As a result, log data above this depth level should be used with caution.
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 392. 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:
Tanzhuo Liu
Phone: 845-365-8630
Fax: 845-365-3182
E-mail: Tanzhuo Liu
Gilles Guerin
Phone: 845-365-8671
Fax: 845-365-3182
E-mail: Gilles Guerin