Standard Wireline Data Processing
IODP logging
contractor: USIO/LDEO
Hole: U1390A
Expedition: 339
Location: Gulf of Cadiz
Latitude: 36° 19.0387' N
Longitude: 7° 43.0812' W
Logging date:
Sea floor
depth (driller's):
1005.1 m DRF
Sea floor
depth (logger's):
1004 m WRF (HRLA/HLDS/EDTC-B/HNGS Main Run)
Sea floor depth (logger's): 1004 m WRF (FMS/DSI/GPIT/EDTC-B Pass 2)
Total
penetration: 1355.1 m DRF (350.1 m DSF)
Total core recovered: 325.9 m (93.1 % of cored section)
Oldest sediment recovered: Pleistocene
Lithologies: nannofossil mud, silty mud and silty 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 2012.
| Tool string | Run/Pass
|
Top depth (m WMSF) | Bottom depth (m WMSF) | Pipe depth (m WMSF) | Notes |
1. HRLA/HLDS/HNGS/EDTC-B
|
Downlog
|
95 |
Invalid HLDS
|
||
Repeat Run |
|
||||
Main Run |
95 |
Reference |
|||
2. FMS/DSI/EDTC-B
|
Downlog
|
95 |
Caliper closed |
||
Pass 1
|
|||||
Pass 2
|
95 |
Hole U1390A was prepared for logging with a wiper trip, then flushed with 20 barrels of sepiolite mud and displaced with 124 barrels of heavy (10.5 ppg, barite weighted) mud.
Maximum ship heave was generally ~1.5 m peak to peak. 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 1004 m WRF. This differs by 1.1 m from the sea floor depth given by the drillers (see above). The logs were depth-shifted to the sea floor and then depth-matched to the gamma ray log from the main run of the HRLA/HLDS/HNGS/EDTC-B (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.
Acoustic data. The dipole shear sonic imager (DSI) was run in Monopole P&S (standard frequency), Upper Dipole (standard frequency), and Lower Dipole (low frequency) modes. The shear and compresional slowness data are generally of good quality and have been converted to acoustic velocities. 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 also on the FMS tool (C1 and C2). The hole diameter was very rugose with many narrow sections of washouts.
Data noise was observed in the HRLA data when the head of the tool string emerged from the pipe.
The density and photoelectric effect (PEF) logs show anomalously high values below 185 WMSF due to the use of barite-weighted mud. 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 336.
For further questions about the logs, please contact:
Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia
Tanzhuo Liu
Phone: 845-365-8630
Fax: 845-365-3182
E-mail: Tanzhuo Liu