Standard Wireline Data Processing
IODP logging contractor: USIO/LDEO
Hole: U1352B
Expedition: 317
Location: Canterbury Basin (SW Pacific Ocean)
Latitude: 44° 56.2558' S
Longitude: 172° 1.3630' E
Logging date: December 4-5, 2009
Sea floor depth (driller's): 354.6 m DRF
Sea floor depth (logger's): 355.5 m WRF (APS/HLDS/GPIT/HNGS)
Total penetration: 1185.5 m DRF (830.9 m DSF)
Total core recovered: 614.3 m ( 74 % of cored section)
Oldest sediment recovered: late Pliocene
Lithology: mud, sandy mud, and muddy 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 December 2009.
| Tool string | Pass
|
Top depth (m WMSF) | Bottom depth (m WMSF) | Pipe depth (m WMSF) | Notes |
1.DIT/APS/HLDS/HNGS
|
Downlog
|
82 |
Invalid HLDS |
||
Repeat
|
Open hole |
||||
Main
|
81 |
Reference |
|||
2.FMS/DSI/GPIT/HNGS
|
Downlog
|
81 |
Calipers closed |
||
Pass 1
|
Open Hole |
||||
Pass 2
|
81.7 |
The hole was drilled to a total depth of 830.9 m DSF and then conditioned for logging by sweeping for few hours with 50 bbl of sepiolite/attapulgite mud. Due to recovery operations at the last site, mud supplies on the ship were limited, so it was decided to displace this hole with seawater rather than logging mud. The logging operations began with the DIT/APS/HLDS/GPIT/HNGS tool string for three passes, followed by the FMS/DSI/GPIT/HNGS tool string for three passes as well. Since the sea state was relatively calm with a peak-to-peak heave of ~ 0.4 m or less, the wireline heave compensator was not used.
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 based on the logger's sea floor depth of - 355.5 m WRF. The sea floor depth was determined by the step in gamma ray values observed on the DIT/APS/HLDS/GPIT/HNGS main pass. The depth-shifted logs were then depth-matched to those of DIT main pass (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
and HLDS 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) 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.
Acoustic data. The dipole shear sonic imager (DSI) was operated with P&S monopole, Upper Dipole, and Lower Dipole modes. The P&S monopole was run in standard frequency mode during Pass 1. Medium frequency modewas used during the downlog and Pass 2. The upper dipole was run in standard frequency mode in all three passes while the lower dipole was run in low frequency mode. 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 (HLDS). The caliper logs indicate that the upper part of the borehole (above 150 m WMSF) was washed out to the degree (>14-19") where it may have 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 317.
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