Standard Wireline Data Processing
Science operator: Texas A&M University
Hole: U1499B
Expedition: 367
Location: China Sea Rifted Margin (South China Sea)
Latitude: 18° 27.5705' N
Longitude: 115°41.5990' E
Logging date: March 7-8, 2017
Sea floor depth (driller's): 3769 m DRF
Sea floor depth (logger's): 3770 m WRF (FMS/GPIT/EDTC-B/HNGS main run)
Total penetration: 4850.8 DRF (1081.8 m DSF)
Total core recovered: 150.64 m (35.3%)
Oldest sediment recovered:
Lithology: Sandstone and claystone, with siltstone interbeds. Sections with low recovery assumed to be primarily composed of non-lifthified sand (618 - 761 m DSF). Claystone with siltstone, calcareous-rich claystone with silt and foraminifer sandstone interbeds from 761 to 892 m DSF. Clay-rich chalk carbonate from 892 to 930 m DSF. Gravel with silty sandstone interbeds, fragmented cores recovered as pebbles/cobbles from 933 to 1081 m DSF.
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 March 2017.
Tool string |
Run
|
Top depth (m WMSF) |
Bottom depth (m WMSF) |
Drill Pipe/Casing (m WMSF) |
Notes |
1. HRLA/HLDS/DSI/HNGS/EDTC-B
|
Downlog
|
980 |
81/651 |
Calipers closed. Invalid HLDS data. |
|
Repeat
|
848 |
Recorded open hole
|
|||
Main
|
980 |
81/651 |
|||
2. FMS/GPIT/EDTC-B/HNGS |
Downlog
|
997 |
81/651
|
Calipers closed. Invalid FMS data. |
|
Repeat
|
997 |
Recorded open hole
|
|||
Main
|
997 |
81/651 |
Depth Reference |
This hole was encased with 10 3/4" 44.5 lb/ft casing pipes to a depth of 651 m DSF (4420 m DRF) before RCB coring with 9 7/8" bit to a total depth of 1081 m DSF (4850 m DRF). The hole could not be drilled any deeper, possibly due to gravel material or sand accumulating at the bottom of the hole, which caused high torque at the bit. The hole was prepared for logging by sweeping seawater and 11 lb/gal heavy mud with barite from 780 m DSF (4549 m WRF) in order to enhance borehole stability. The hole was believed to be stable enough to run the density tool (HLDS) with a radioactive source. Since acquisition of sonic compressional data was a high priority, the first logging tool string was modified by adding the dipole sonic (DSI) and removing the porosity (APS) and magnetic susceptiblity (MSS) tools.
Average heave was about 0.5 m. The heave compensator was utilized during the logging operations in open hole.
The depths in
the table are for the processed logs (after depth shift to the sea floor and depth matching between passes). 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 shift to sea floor and depth match.
The original logs were first shifted to the sea floor (-3770 m). The sea floor depth
was determined by the step in gamma ray values at 3770 m WRF on the FMS/GPIT/EDTC-B/HNGS main pass. This differs by 1 m from 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 FMS/GPIT/EDTC-B/HNGS main pass.
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 HLDS and HRLA data were corrected for hole size during the recording. The HNGS data were corrected for hole size and mud weight 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. 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 P&S monopole and upper dipole (standard frequency) and lower dipole (low frequency) modes. Since sonic data were a high priority at this hole, the Schlumberger engineer re-processed the labeling for both compressional and shear data in order to improve the data quality. Compressional and shear velocities were computed from the reprocessed delay times.
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 density log). Good repeatibility is observed on the gamma ray logs. The density data, whose quality depends from a good contact of the sensors with the borehole wall, is provided only in the open hole section below 651 m WMSF. Whereas the density log shows a good correlation with the resistivity log from 670 to 780 m WMSF, the photoelectric effect (PEF) is above its normal range of 0-10 barns/e-, an effect of the presence of barite from the pumped heavy mud in the hole above 780 m WMSF.
Hole diameter was recorded by the caliper on the HLDS
tool (LCAL) and the FMS tool (C1 and C2). A wide (>12") and/or irregular borehole affects most recordings, particularly those that require eccentralization and a good contact with the borehole wall (HLDS). The hole size was variable with maximum readings of 17 inches from the casing depth at 651 m WMSF to about 950 m WMSF. Below this depth the hole size was around 12 inches.
The gamma ray logs recorded through the encased hole section, bottom hole assembly (BHA) and drill pipe should be used only qualitatively, because of the attenuation on the incoming signal. The gamma ray logs show the bottom of the drill pipe at 81 m WMSF.
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 further questions about the logs, if the hole is still under moratorium please contact the staff scientist of the expedition.
After the moratorium period you may direct your questions to:
Tanzhuo Liu
Phone: 845-365-8630
Fax: 845-365-3182
E-mail: Tanzhuo Liu
Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia