Standard Wireline Data Processing
Science operator: Texas A&M University
Hole: U1560B
Expedition: 393
Location: Mid-Atlantic Ridge (S Atlantic Ocean)
Latitude: 30° 24.2057' S
Longitude: 16° 55.3702' W
Logging date: July 28, 2022
Sea floor depth (driller's): 3734.8 m DRF
Sea floor depth (logger's): 3736.0 m WRF
Total penetration: 4051 m DRF (316.2 m DSF)
Total core recovered: 74.8 m (38.9% of cored section)
Oldest sediment recovered: Middle Miocene
Lithology: nannofossil ooze with clay; basalt; pillow, sheets and lava flows
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 2022.
| Tool string |
Pass
|
Top depth (m WMSF) | Bottom depth (m WMSF) | Pipe depth (m WMSF) | Notes |
|
1. MSS/HRLA/APS/HLDS/HNGS/EDTC-B
|
Downlog
|
0
|
316
|
26.5
|
Caliper closed. Invalid HLDS and APS. Reference run for depth matching
|
|
Pass 1
|
96
|
309
|
Recorded casing/open hole
|
||
|
Pass 2
|
80
|
313.5
|
Recorded casing/open hole
|
||
|
2. FMS/DSI/HNGS
|
Downlog
|
0
|
310
|
26.5
|
Caliper closed. Invalid FMS
|
|
Pass 1
|
127
|
309
|
Recorded open hole
|
||
|
Pass 2
|
127.5
|
309
|
Recorded open hole
|
||
|
3. UBI/HNGS
|
Downlog
|
0
|
309
|
26.5
|
Invalid UBI. |
|
Pass 1
|
120.5
|
287
|
Recorded open hole
|
||
|
Pass 2
|
0
|
308
|
Recorded casing/open hole
|
This is a re-entry of the previously cased hole. After the completion of coring operations, the MSS/HRLA/APS/HLDS/HNGS/EDTC-B tool string was deployed for logging, followed by the FMS/DSI/HNGS and UBI/HNGS tool strings. The downlogs of the Triple Combo and FMS tool strings were run with the caliper closed.
The Wireline Heave Compensator (WHC) was used in the open hole interval to counter the ship heave while logging. Sea condition was high with ship heave in the 2-3 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.
For hole U1560B, the Triple Combo uplogs were depth-matched via the resistivity log (RT_HRLT) to their corresponding downlog (reference run). The FMS image of pass 1 was first depth matched with the resistivity log of the Triple Combo downlog and then with the FMS image of pass 2. The FMS and UBI downlogs and UBI passes 1 and 2 were finally depth matched via the gamma ray log of the reference run.
The depth-matched logs were then depth-shifted to the sea floor. The sea floor depth was determined by the step in gamma ray values at 3736.0 m WRF observed on the reference run. This differs by 1.2 m from the sea floor depth given by the drillers (see above).
Environmental corrections. The HNGS and HRLA data were corrected for hole size during the recording. The APS data were corrected for hole size and standoff during the recording.
High-resolution data. Gamma ray data from the EDTC-B and porosity data from the APS tools were recorded at sampling rates of 15.24 and 5.08 cm. The HRLA data were 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: P&S monopole, upper and lower dipoles, and stoneley. 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). For hole U1560B, the repeatibility is poor among gamma ray logs due to their low values in the range of 0-25 gAPI, which makes it difficult to depth-match logs from different tool strings. The repeatibility is generally good among resistivity, density and porosity, and some sonic logs among different passes.
Gamma ray and other logs recorded through the cased hole section (26.5-120.8 m WMSF) and drill pipe should be used only qualitatively, because of the attenuation of the incoming signals by the drill pipe and cased layer of the borehole wall.
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 U1560B, the caliper was near bit size of 9 7/8" for over half of the logged open hole interval. Washouts exist at the depth interval of 125-187 m WMSF and also around 245-260 m WMSF, which may have impaired the quality of the log data.
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 393.
For any question about the data or about the LogDB database, please contact LogDB support: logdb@ldeo.columbia.edu.