Standard Wireline Data Processing
Science operator: Texas A&M University
Hole: U1500B
Expedition: 367
Location: China Sea Rifted Margin (South China Sea)
Latitude: 18° 18.2707' N
Longitude: 116° 13.1951' E
Logging date: April 6-7, 2017
Sea floor depth (driller's): 3812.8 m DRF
Sea floor depth (logger's): 3812.8 m WRF
Total penetration: 5341.8 m DRF (1529 m DSF)
Total core recovered: 278.79 m ( 40.8 % of cored section)
Oldest sediment recovered: 16 Ma (Lower-mid Miocene)
Lithology: Sediments: clay, silt and sand; claystone/siltstone/sandstone. Igneous rocks: basalts
The logging data were recorded by Schlumberger in DLIS format. Data were processed at the Borehole Research Group of the Lamont-Doherty Earth Observatory in April 2017.
| Tool string |
Run
|
Top depth (m WMSF) |
Bottom depth (m WMSF) |
Pipe/Casing depth (m WMSF) |
Notes |
|
1. HRLA/DSI/HLDS/EDTC-B/HNGS
|
Down
|
0
|
1131
|
31.5 / 842
|
Reference run. Caliper closed. Invalid HLDS.
|
|
Repeat
|
977
|
1133
|
recorded open hole
|
HLDS invalid
|
|
|
Main
|
0
|
1119
|
31.5 / 842
|
HLDS invalid
|
|
|
2. FMS/GPIT/EDTC-B/HNGS
|
Uplog
|
0
|
1040
|
31.5 / 842
|
|
|
3. VSI/EDTC
|
783.2
|
783.2
|
31.5 / 842
|
1 station
|
After a 10 3/4 in casing was installed at 4654.8 m DRF (842 m DSF), RCB coring operations resumed to a total depth of 5341.8 m DRF (1529 m DSF). The drillpipe was placed at 3844.3 m DRF (31.5 m DSF). The drilling operations were uneventful, until the drill pipe got stuck for about 2.5 hrs while it was pulled up to the sea floor. As a precaution, it was thus decided to run a modified tool string with the HLDS caliper but no nuclear source to measure density.
The first tool string HRLA/DSI/HLDS/EDTC-B/HNGS could not pass a bridge at about 4944 m WRF (1131 m WSF). It acquired a downlog, and two upward passes.
The second tool string, comprising of the FMS/GPIT/EDTC-B/HNGS, was stuck by a bridge at about 4855 m WRF, 90 m shallower than the first tool string. No downlog was acquired in order to save time; a single uplog was recorded from the bridge to the sea floor.
The final tool string included the VSI and the EDTC-B for depth correlation with the other logging runs. A few stations were attempted in open hole but none of them yielded usable shots. One station was successful through the 10 3/4 in casing at 4596 m WRF (783.2 m WSF) where a compressional sonic curve recorded good coherency through the casing, thus indicating good connection with the formation. The 13 shots recorded were somehow noisy but at least 6 with similar transit times were stacked. They delivered a corrected transit time of 2.9386 sec, corresponding to the value expected by the shipboard party.
The average heave was less than 0.5 m; the Wireline Heave Compensator was used only when the tools were recording in open hole.
Depth shift to sea floor and depth match. The original logs were first shifted to the sea floor (- 3812.8 m). The sea floor depth was determined by the step in gamma ray values at 3812.8 m WRF. This coincides with the sea floor depth given by the drillers (see above). The depth-shifted logs have then been depth-matched to the gamma ray log from the downlog of the tool string. The downlog was chosen as the reference run for depth matching.
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 that were 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.
Environmental corrections. The HNGS and HRLA data were corrected for hole size during the recording.
High-resolution data. The Gamma Ray data from the EDTC tool and the resistivity data from the HRLA tool are available with 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 (standard frequency) and lower dipole (low frequency). The velocities were computed from the delay times. They are generally of acceptable quality. Better results can be obtained from processing of the sonic waveforms.
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 the casing and drill pipe should be used only qualitatively because of the attenuation of the incoming signal. The casing shoe is at 842 m WMSF.
Hole diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL) and by the FMS tool (C1 and C2). The hole is large (>15 in) and irregular from the casing to about 1020 m WMSF. It is generally less than 13 inches in diameter below that depth.
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 367.
For any question about the data or about the LogDB database, please contact LogDB support: logdb@ldeo.columbia.edu.