Standard Wireline Data Processing
Science operator: Texas A&M University
Hole: U1530A
Expedition: 376
Location: Brothers Volcano SW Pacific Ocean
Latitude: 34° 51.6588' S
Longitude: 179° 3.4572' E
Logging date: June 19-20, 2018
Sea floor depth (driller's): 1606 m DRF
Sea floor depth (logger's): 1601 m WRF
Total penetration: 2054.1 m DRF (453.1 m DSF)
Total core recovered: 76.77 m (16.9 % of cored section)
Oldest sediment recovered: n/a
Lithology: volcaniclastic rocks (lapillistone, lapilli-tuff and tuff-breccia)
The logging data was recorded by Schlumberger in DLIS format. Data were processed at the Borehole Research Group of the Lamont-Doherty Earth Observatory in June 2018.
| Tool string |
Pass
|
Top depth (m WMSF) | Bottom depth (m WMSF) | Pipe depth (m WMSF) | Notes |
|
1. HRLA/APS/HLDS/EDTC-B/HNGS
|
Downlog 1
|
0
|
434
|
69
|
Caliper closed. Invalid APS and HLDS.
|
|
Downlog 2
|
226
|
434
|
recorded openhole
|
Caliper closed. Invalid APS and HLDS.
|
|
|
Repeat
|
273
|
442
|
recorded openhole
|
||
|
Main
|
0
|
442
|
69
|
Depth reference run.
|
|
|
2. FMS/DSI/GPIT/EDTC-B/HNGS
|
Downlog
|
0
|
441
|
Caliper closed. Invalid FMS images.
|
|
|
Pass 1
|
116
|
442
|
recorded openhole
|
||
|
Pass 2
|
0
|
439
|
69
|
After rotary coring was completed, preparations were made for logging in a high temperature environment. The HNGS tool was pre-cooled to -20 C for several hours prior to logging. The HRLA/APS/HLDS/EDTC-B/HNGS tool string was run first. The first downlog reached total depth, with the logging head mud temperature (MTEM) measuring approximately 92 C. A repeat pass was recorded next, followed by a second downlog requested by the co-chiefs to measure a shoreter second temperature profile, and by a main pass up to the sea floor. The maximum temperature value was over 94 C, recorded during the main pass. The caliper was closed during both downlogs, therefore both porosity (APS) and density (HLDS) readings are invalid.
The second deployment consisted of the FMS/DSI/GPIT/EDTC-B/HNGS tool string, which acquired a downlog with the caliper closed and two uplogs. The latter had some difficulty re-entering the drill pipe: It was later observed that one of the centralizer springs was worn out, with some notches on the side that may have cause the tool string to get hung, and a large bend possibly cause by a loose rock. The temperature measured at the bottom of the hole during the FMS deployemnt were in the 35-40 C range, indicating that the hole had cooled considerably during the logging operations.
The ship heave was on average 0.5-1 m, therefore the heave compensator (WHC) was used whenever the tools were in open hole.
The depths in the table are for the processed logs (after depth matching between passes and depth shift to the sea floor). Generally, 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 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 main run of the HRLA/APS/HLDS/EDTC-B/HNGS tool string. 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.
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 1601 m WRF. This differs by 5 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 and HLDS data were corrected for standoff and hole size respectively during the recording.
High-resolution data. Bulk density (HLDS) and neutron porosity (APS) data were recorded at sampling rates of 2.54 and 5.08 cm, respectively, 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 is 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 is also acquired every 5.08 cm; in the database it was 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 dipole (downlog), P&S monopole, upper dipole, Stoneley, and cross-dipole (passes 1 and 2). The velocities were computed from the delay times. The compressional velocities are of acceptable quality except in the following intervals: 110-120, 149-160, 184-217, 337-350 m WMSF. Post-cruise processing of the sonic waveforms is strongly recommended in order to obtain better velocity results.
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). The repeatability between the HRLA/APS/HLDS/EDTC-B/HNGS passes is very good, with some exceptions where the hole was very enlarged.
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.
A wide (>12") and/or irregular borehole affects most recordings, particularly those that require eccentralization and a good contact with the borehole wall (APS, HLDS). Hole diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL) and by the FMS tool (C1 and C2). The calipers show a very large hole, with most readings in the 15-17" range. The HLDS caliper reached its maximum extension in the 170-220, 268-300 and 325-350 m WMSF intervals, indicating that the hole may have been even larger.
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 376.
For any question about the data or about the LogDB database, please contact LogDB support: logdb@ldeo.columbia.edu.