Standard Wireline Data Processing
Science operator: Texas A&M University
Hole: U1564F
Expedition: 395
Location: Reykjanes Mid-Ocean Ridge, North Atlantic
Latitude: 59° 51.0363' N
Longitude: 23° 15.9840' W
Logging date: August 9, 2023
Sea floor depth (driller's): 2219.5 m DRF
Sea floor depth (logger's): 2219.5 m WRF
Total penetration: 3389.2 m DRF (1169.7 m DSF)
Total core recovered: 434.15 m (75.9 % of cored section)
Oldest sediment recovered: Early Oligocene (~32.3 Ma)
Lithology: Silty clay and claystone with nannofossils, nannofossil silty clay/claystone, nannofossil chalk with silty clay, and basement 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 August 2023.
| Tool string |
Pass
|
Top depth (m WMSF) | Bottom depth (m WMSF) | Casing depth (m WMSF) | Notes |
|
1. MSS/HRLA/HLDS/APS/HNGS/EDTC-B
|
Downlog
|
0
|
1171.1
|
551
|
Caliper closed. Invalid HLDS, MSS and APS.
|
|
Repeat
|
1057.2
|
1171.2
|
Recorded open hole
|
Invalid MSS and APS. |
|
|
Main
|
0
|
1170.6
|
551
|
Invalid MSS and APS. |
|
| 2. FMS/DSI/HNGS/EDTC-B |
Downlog
|
508.0
|
1116.2
|
551
|
Caliper closed. Invalid FMS. |
|
Pass 1
|
539.5
|
1169.3
|
551
|
Invalid DSI. |
|
|
Pass 2
|
528.3
|
1169.6
|
551
|
Invalid DSI. |
|
| 3. UBI/HNGS/EDTC-B |
Downlog
|
524.3
|
1165.6
|
551
|
Invalid UBI. |
|
Repeat
|
987.6
|
1164.4
|
Recorded open hole
|
High-resolution UBI images. | |
|
Main
|
539.8
|
1163.9
|
551
|
Low-resolution UBI images. |
After the completion of coring operations and the mud sweeping of the hole, three tool strings were deployed for logging in the following order. The triple-combo tool string of MSS/HRLA/HLDS/APS/HNGS/EDTC-B was first run for downlog, repeat and main passes. Due to the malfunction of MSS and APS tools during the logging operation, the magnetic susceptibility and porosity data were not collected for this hole. The FMS and sonic tool string of FMS/DSI/HNGS/EDTC-B was then run for downlog, pass 1 and pass 2. Again, due to some technical problems with the DSI tool, the sonic data were not acquired for passes 1 and 2. The UBI tool string of UBI/HNGS/EDTC-B was last run for downlog, repeat and main passes, yielding high-reslolution images from the repeat pass and standard-resolution images from the main pass.
The Wireline Heave Compensator (WHC) was used in the open hole interval to counter the ship heave while logging. Sea condition was high with peak-to-peak heave in the 2.5 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. 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.
During this processing, the original logs acquired from all three tool strings were depth-matched using the gamma ray log (HSGR) from the triple combo main pass as a reference. 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 2219.5 m WRF observed on the reference log. 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.
Acoustic data. The dipole shear sonic imager (DSI) was operated in the following modes with standard frequency: P&S monopole, upper and lower dipole, and Stoneley. The sonic velocities were computed from the delay times. Compressional, lower and upper dipole shear velocities from the downlog are 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), drill pipe (0 - 57 m WMSF) and cased hole interval (0 - 551 m WMSF ) 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 hole U1564F, the caliper was around 12" or less for most of the logged hole interval below the casing depth of 551 m WMSF, except for a washout between 1042 and 1057 m WMSF. As a result, log data such as gamma ray and density at the washout interval 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 395.
For any question about the data or about the LogDB database, please contact LogDB support: logdb@ldeo.columbia.edu.