Standard Wireline Data Processing
IODP logging contractor: USIO/LDEO
Hole: U1341B
Expedition: 323
Location: Bowers Ridge (Bering Sea)
Latitude: 54° 2.0 ' N
Longitude: 179° 5.0 ' E
Logging date: July 31-August 1, 2009
Sea floor depth (driller's): 2150.9 m DRF
Sea floor depth (logger's): 2150 m WRF
Total penetration: 2750.9 m DRF (600 m DSF)
Total core recovered: 589.3 m (98.7 % of cored section)
Oldest sediment recovered:
Lithology: Alternating dark grayish olive diatom silt and clay to light olive green diatom ooze; slightly to moderately bioturbated; occasional ash layers with volcanic clasts; laminated or thin layered intervals, ice-rafted debris, and dolomite nodules.
The logging data
was recorded by Schlumberger in DLIS format. Data were processed on the JOIDES Resolution in August 2009.
| Tool string | Pass |
Top depth (mbsf) | Bottom depth (mbsf) | Pipe depth (mbsf) | Notes |
1.DIT/APS/HLDS/GPIT/HNGS
|
Downlog |
78 |
Invalid HLDS |
||
Repeat
|
Open hole |
||||
Main
|
78 |
Reference |
|||
2. FMS/DSI/GPIT/HNGS
|
Downlog
|
63 |
78 |
No valid FMS image |
|
Pass 1
|
Open hole |
||||
Pass 2 |
78 |
Logging operations were started with the DIT/APS/HLDS/GPIT/HNGS tool string, which recorded data downlog first and then a repeat and main pass uplog. Three passes of the FMS/DSI/GPIT/HNGS tool string were subsequently acquired. The wireline heave compensator was used only during the DIT/APS/HLDS/GPIT/HNGS passes.
The sea was calm, with heave of 0.25 m or less throughout the entire logging session.
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. Sea floor depth was determined by the logger's depth: - 2150 m WRF from the DIT/APS/HLDS/GPIT/HNGS main pass. All of the logs were first depth-shifted to the sea floor (- 2150 m WRF) and then depth-matched to the DIT/APS/HLDS/GPIT/HNGS main pass (used as a 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 HNGS 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 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.
Acoustic data. The dipole shear sonic imager (DSI) was operated in the following modes for three FMS-Sonic passes: downlog with P&S monopole (low frequency), upper dipole (standard frequency), and lower dipole (low frequency); both pass 1 and pass 2 with P&S monopole (standard frequency) and upper dipole (standard frequency) lower dipole (low frequency). Because of the slow formation, the automatic picking of wave arrivals in the sonic waveforms did not provide consistently reliable results. Reprocessing of all the original waveforms was performed to validate the original data or extract meaningful compressional and shear velocities. The most reliable shear velocity value is the one derived from the lower dipole (VS1), where the lower source frequency used generated more cohert waveforms.
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).
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.
Hole diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL) and by 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 (APS, HLDS). The caliper logs indicate that the upper part of the borehole (250-100 m WMSF) was washed out to the degree (>14-19") where it has adversely affected the tool response. Thus, density and porosity logs in this depth interval should be treated with caution.
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 323.
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