Standard Wireline Data Processing
IODP logging contractor: USIO/LDEO
Hole: U1344A
Expedition: 323
Location: Arctic Gateway (Bering Sea)
Latitude: 59° 3.0' N
Longitude: 179° 12.2' W
Logging date: August 18-19, 2009
Sea floor depth (driller's): 3183.4 m DRF
Sea floor depth (logger's): 3184.5 m WRF
Total penetration: 3928.4 m DRF (745 m DSF)
Total core recovered: 648.10 m (87 % of cored section)
Oldest sediment recovered: Early Pleistocene (~ 2 my)
Lithologies: dark greenish gray diatom-bearing silty clay to diatom-rich sandy silt, with occasional sandy layers, pebble size clasts, authigenic carbonate layers, and rare diatom ooze; moderately bioturbated.
Data
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 August 2009.
| Tool string | Pass |
Top depth (mbsf) | Bottom depth (mbsf) | Pipe depth (mbsf) | Notes |
1.DIT/APS/HLDS/GPIT/HNGS
|
Downlog
|
95 |
Invalid HLDS |
||
Repeat
|
Open hole |
||||
Main
|
92.5 |
Reference |
|||
2. FMS/DSI/GPIT/HNGS
|
Downlog
|
95 |
Invalid images |
||
Pass 1
|
Open hole |
||||
|
Pass 2
|
93.5 |
The logging operations started with the DIT/APS/HLDS/GPIT/HNGS, followed by three passes of the FMS/DSI/GPIT.HNGS tool string. Due to a restriction of the borehole wall at ~726 m WMSF, however, the FMS passes could not reach to the total depth of 745 m WMSF. The wireline heave compensator was not used during the entire logging session because of the calm sea state (heave <0.45 m).
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 step in the gamma ray log observed at 3184.5 m WRF on the main pass of the DIT/APS/HLDS/GPIT/HNGS tool string. All of the logs were first depth-shifted to the sea floor (- 3184.5 m WRF) and then depth-matched to DIT/APS/HLDS/GPIT/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.
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.
Gamma Ray data from the SGT tool were recorded at sampling rates of 5.08 and 15.24
cm.
Acoustic data. The dipole shear sonic imager (DSI) was operated in P&S monopole (medium frequency), upper dipole (standard frequency), and lower dipole (low frequency) modes during the downlog and pass 1, and in P&S monopole (standard frequency), upper dipole (standard frequency), and lower dipole (low frequency) during pass 2. 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 (above 320 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 used 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