Standard Wireline Data Processing
IODP logging
contractor: USIO/LDEO
Hole: U1395B
Expedition:
Location: Lesser Antilles, off Montserrat (Caribbean Sea)
Latitude: 16° 29.5985' N
Longitude: 61° 57.0751' W
Logging date:
Sea floor
depth (driller's):
1211.6 m DRF
Sea floor depth (logger's): 1209 m WRF (HRLA/MSS/HLDS/EDTC-B/HNGS main)
Total
penetration: 1414.9 m DRF (203.3 m DSF)
Total core
recovered: 139.54 m (
68.6 % of cored section)
Oldest
sediment recovered:
Lithologies: Volcaniclastic material, turbidites, hemipelagic sediments, ash
layers, some pumice-rich units. Recovery was very poor below 125 m DRF ('chaotic' unit identified from
seismic at ~125-175 m DRF). Some semi-lithified material recovered below 150 m DRF.
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 March 2012.
| Tool string | Pass
|
Top depth (m WMSF) | Bottom depth (m WMSF) | Pipe depth (m WMSF) | Notes |
1. HRLA/HLDS/MSS/EDTC-B/HNGS
|
Downlog
|
81 |
Invalid caliper |
||
Main
|
81 |
Reference |
|||
Repeat
|
recorded open hole |
||||
2. FMS/DSI/GPIT/EDTC-B
|
Downlog
|
81 |
Invalid caliper |
||
Main
|
81 |
||||
Repeat
|
recorded open hole |
Hole U1395B was conditioned for logging with 10.5 lb/gal sepiolite mud. The MSS data channels were not properly recorded owing to some technical problems and therefore no MSS data is available at this hole.
The sea state was low with a peak-to-peak heave of 0.8-1 m or less. Wireline heave compensator was used during the entire logging operations (except for FMS main pass).
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 (- 1209 m). This sea floor depth differs by 2.6 m from that given by the drillers (see above). The depth-shifted logs were then depth-matched to the gamma ray log from the HRLA/HLDS/MSS/EDTC-B/HNGS main run (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 in turn matched to it. 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.
High-resolution data. The HNGS data were corrected for hole size and the HLDS data were corrected for both standoff and hole size during the recording.
Acoustic
data. The dipole sonic imager (DSI) was operated in P&S monopole and Upper and Lower dipole modes. Standard frequency was used in the P&S monopole and upper dipole modes and low frequency in the lower dipole mode. The velocities were computed from the P&S monopole compressional and upper and lower dipole shear slownesses. The sonic data are
generally of good quality although in the larger (>16") top section of the hole (above 101 m WMSF) some of the pickings are rather suspicious. Reprocessing of the sonic waveforms is recommended for better 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). For unknown reasons the HRLA logs are noisy just below the drill pipe.
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). The hole diameter is generally in gauge (~12-14") for the open hole section below 126 m WMSF, but becomes enlarged (>16") from 101 m WMSF to just below the drill pipe.
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 340.
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