Standard Wireline Data Processing
IODP logging contractor: USIO/LDEO
Hole: U1386C
Expedition: 339
Location: Gulf of Cadiz
Latitude: 36° 49.6773' N
Longitude: 7° 45.3165' W
Logging date: December 7, 2011
Sea floor depth (driller's): 573.2 m DRF
Sea floor depth (logger's): 573 m WRF
Total penetration: 1098 m DRF (526 m DSF)
Total core recovered: 58 % of cored section in hole C (99% in Hole A and 91% in Hole B)
Oldest sediment recovered: Late Miocene
Lithology: Calcareous silty mud, sandy silt and silty sand coarse sand.
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 December 2011.
| Tool string | Run/Pass
|
Top depth (m WMSF) | Bottom depth (m WMSF) | Pipe depth (m WMSF) | Notes |
1. HRLA/DIT/HLDS/HNGS/EDTC-B
|
Downlog
|
101.5 |
Invalid HLDS
|
||
Repeat Run
|
101.5 |
|
|||
Main Run
|
101.5 |
Reference |
|||
2. FMS/DSI/HNGS/EDTC-B
|
Downlog
|
101.5 |
Caliper closed |
||
Pass 1
|
101.5 |
||||
Pass 2
|
101.5 |
||||
3. VSIT/EDTC-B |
|
12 levels, 115 shots |
Hole U1386C was prepared for logging with a wiper trip and then flushed with high-viscosity mud and displaced with 172 barrels of heavy (10.5 ppg, barite weighted) mud.
Maximum peak to peak ship heave was about ~0.5 m. The wireline heave compensator was used during the logging operation.
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 sea floor depth was determined by the step in gamma ray values at 573 m WRF. The logs were depth-shifted to the sea floor and then depth-matched to the gamma ray log from the mainain run of the HRLA/DIT/HLDS/HNGS/EDTC-B tool string (reference).
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 the hole size during the recording.
High-resolution data. Bulk density (HLDS) data were recorded at sampling rates 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 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 and HNGS tools were recorded at sampling rates of 5.08 and 15.24 cm respectively.
Acoustic data. The dipole shear sonic imager (DSI) was run in Monopole P&S (standard frequency), Upper Dipole (medium frequency), and Lower Dipole (standard frequency) modes. The shear and compressional slowness data are generally of good quality and have been converted to acoustic velocities. The downlog sonic waveforms looked good but there were many miss-picks of the P-wave velocity in the upper part of the hole. The shear-wave velocity data from Lower Dipole (DTSM) were of poor quality between 102 and 205 m WMSF, but of good quality below 205 m WMSF. Reprocessing of the original sonic waveforms is always recommended to obtain more reliable 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 density log).
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 (HLDS). Hole diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL) and on the FMS tool (C1 and C2). In general the logs were of very good quality. The borehole was not especially wide, but it was rugose (it varied a lot on the meter and sub-meter scale). The density log seemed especially sensitive to the washouts. The HRLA and DIT resistivities overlay quite well. The density and photoelectric effect (PEF) logs show anomalously high values due to the use of barite mud, especially where the borehole was wider. They should be used qualitatively only.
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 reports,
Proceedings of the Integrated Drilling Program, Expedition 339.
For further questions about the logs, please contact:
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