Standard Wireline Data Processing
Science operator: Texas A&M University
Hole: U1601C
Expedition: 399
Location: Building Blocks of Life, Atlantis Massif
Latitude: 36° 7.9417' N
Longitude: 42° 7.2072' E
Logging date: May 26, 2023
Sea floor depth (driller's): 861 m DRF
Sea floor depth (logger's): 861 m WRF
Total penetration: 2056.1 m DRF (1195.1 m DSF)
Total core recovered: 843.2 m (71.6 % of cored section)
Oldest sediment recovered: none
Lithology: serpentinized peridotites; gabbro
The logging data were recorded by Schlumberger in DLIS format. Data were processed at the Borehole Research Group of Lamont-Doherty Earth Observatory in June 2023.
| Tool string |
Pass
|
Top depth (m WMSF) | Bottom depth (m WMSF) | Pipe depth (m WMSF) | Notes |
|
1. HLDS/HNGS/EDTC-B
|
Downlog
|
0
|
1074.6
|
29
|
Caliper closed. Invalid HLDS.
|
|
uplog
|
0
|
1076.0
|
29
|
||
| 2. UBI/HRLA/APS/EDTC-B |
Downlog
|
0
|
207.6
|
29
|
EDTC-B tool malfunctioned. |
|
Uplog
|
273
|
1073.6
|
Recorded open hole
|
EDTC-B tool malfunctioned. |
|
| 3. MSS/HNGS/EDTC-B |
Downlog
|
0
|
1075.1
|
29
|
EDTC-B tool malfunctioned. Reference run for depth matching. |
|
Downlog
|
0
|
1075.6
|
29
|
EDTC-B tool malfunctioned. |
|
| 4. FMS/DSI/HNGS/EDTC-B |
Downlog
|
0
|
1075.7
|
29
|
EDTC-B tool malfunctioned. |
|
Pass 1
|
72.8
|
1071.9
|
Recorded open hole
|
EDTC-B tool malfunctioned. |
|
|
Pass 2
|
0
|
1075.4
|
29
|
EDTC-B tool malfunctioned. |
|
| 5. VSI/EDTC-B |
Downlog
|
0
|
1069.4
|
29
|
|
|
Uplog
|
0
|
1069.2
|
29
|
|
After the completion of coring operations, a total of five tool strings were deployed for logging. Both downlog and uplog were run with tool strings of HLDS/HNGS/EDTC-B, UBI/HRLA/APS/EDTC-B, MSS/HNGS/EDTC-B, and VSI/EDTC-B. Tool string of FMS/DSI/HNGS/EDTC-B was run for downlog, pass 1 and pass 2. The downlog of HLDS/HNGS/EDTC-B was run with the caliper closed and the HLDS radioactive source turned off. EDTC-B in the tool strings of HLDS/HNGS/EDTC-B and VSI/EDTC-B functioned normally, yielding gamma ray logs comparable to those from HNGS. EDTC-B from the other three tool strings malfunctioned during the logging operations, yielding no usable gamma ray data as a result.
The Wireline Heave Compensator (WHC) was used in the open hole interval to counter the ship heave while logging. Sea condition was low with peak-to-peak heave in the 0.5 m range.
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 from HLDS/HNGS/EDTC-B and FMS/DSI/HNGS/EDTC-B were depth-matched to the gamma ray downlog from MSS/HNGS/EDTC-B. The latter was chosen as a reference because it was the longest pass logging across the sea floor. The depth-matched FMS image (pass 2) was used as a reference log for depth-matching of the original logs from UBI/HRLA/APS/EDTC-B, while the depth-matched gamma ray log of UBI/HRLA/APS/EDTC-B was used for depth-matching of the original logs from the VSI/EDTC-B tool string. Note that there was a 3-m offset between the gamma ray features from the HLDS/HNGS/EDTC-B uplog and the reference run around 38-41 m WMSF, due likely to the missed wrap on the drum. As a results, all logs from the HLDS/HNGS/ETCD-B uplog pass above this depth interval should be used with caution.
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. The sea floor depth was determined by the step in gamma ray values at 861 m WRF from the MSS/HNGS/EDTC-B downlog. This value is the same as the sea floor depth given by the drillers (see above).
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. The HRLA data were also acquired every 5.08 cm; in the database they were resampled at 15.24 cm, for ease of comparison with the other logs.
Porosity data. The porosity data acquired from APS were spiky, and should thus be used with caution.
Acoustic data. The dipole shear sonic imager (DSI) was operated in the following modes: P&S monopole, upper and lower dipole, and Stoneley on all three passes. The velocities were computed from the delay times. Compressional, lower and upper dipole shear velocities 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), cased hole interval (fom the seafloor to 23 m WMSF ) 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. For U1601C, the caliper was around 12" or less for the nearly entire logged hole interval, except for two washouts at 144 m and 160 m WMSF. As a result, log data such as gamma ray, density, and magnetic susceptibility around the two wahsouts 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 399.
For any question about the data or about the LogDB database, please contact LogDB support: logdb@ldeo.columbia.edu.