Standard Wireline Data Processing
IODP logging contractor: USIO/LDEO
Hole: U1339D
Expedition: 323
Location: Umnak Plateau (Bering Sea)
Latitude: 54° 40.1819 ' N
Longitude: 169° 58.8909 ' W
Logging date: July 20-21, 2009
Sea floor depth (driller's): 1878.4 m DRF
Sea floor depth (logger's): 1876.5 m WRF (DIT/HLDS/APS/GPIT/HNGS main)
Sea floor depth (logger's): 1875 m WRF (FMS/DSI/GPIT/HNGS pass 2)
Total penetration: 2084.4 m DRF
Total core recovered: 205.93 m (103 % of cored section)
Oldest sediment recovered:
Lithology: Green to grayish green diatomaceous ooze and diatomaceous silts with frequent ash layers, variable amounts of dispersed vitric ash, occasional thin IRD layers, burrows and isolated pebbles.
The logging data
was recorded by Schlumberger in DLIS format. Data were processed on the JOIDES Resolution in July 2009.
| Tool string | Pass |
Top depth (mbsf) | Bottom depth (mbsf) | Pipe depth (mbsf) | Notes |
1.DIT/APS/HLDS/GPIT/HNGS
|
Downlog |
84 |
Invalid HLDS |
||
Repeat Lower
|
Open hole |
||||
Main
|
84 |
||||
2. FMS/DSI/GPIT/HNGS
|
Downlog
|
84 |
No valid FMS image |
||
Pass 1
|
Open hole |
||||
Pass 2 |
84 |
Reference |
Logging operations started with the DIT/APS/HLDS/GPIT/HNGS tool string, which recorded data downlog first and then two repeat (upper and lower) and a main pass. The repeat upper pass (about 40 m long below the drill pipe) was logged while the caliper arm was jammed, so the log data might have been impaired and therefore was not processed. Three passes of the FMSDSI/GPIT/HNGS tool string were subsequently acquired without incidents. The wireline heave compensator was used throughout the logging operation, even though the sea state was very calm, with heave of 0.2 meters or less.
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. Two sea floor depths were determined by the loggerŐs depth: -1876.5 mbrf from DIT/APS/HLDS/GPIT/HNGS main pass and -1875 mbrf from the FMS/DSI/GPIT/HNGS pass 2. The DIT/APS/HLDS/GPIT/HNGS logs were first shifted to the sea floor (-1876.5 m) and then depth-matched to the gamma ray log from the depth-shifted (-1875 mbrf) FMS pass 2 (reference). FMS downlog and pass 1 were first shifted to the sea floor (-1875 mbsf) and then depth-matched to the gamma ray log from the depth-shifted FMS pass 2.
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 mode for all three FMS-Sonic passes: P&S monopole and upper dipole (standard frequency) and 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). The HLDS caliper was kept closed during the downlog. It reached 12-13" in most of the logged interval (105-183 mbsf). A wide (>12") and/or irregular borehole affects most recordings, particularly those that require eccentralization and a good contact with the borehole wall (HLDS). Therefore, log data from the >12" portion of the hole and bulk density data from the downlog (no correction for borehole size) should be used with caution. Also, due to a slightly bent caliper arm during the main pass, a 1.62" correction was systematically added to the original caliper data during the processing.
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