Standard Wireline Data Processing
IODP logging contractor: USIO/LDEO
Hole: U1376A
Expedition: 330
Location: Louisville Sea Mount (Central S Pacific Ocean)
Latitude: 32° 12.99' S
Longitude: 171° 52.84 ' W
Logging date: February 2-3, 2011
Sea floor depth (driller's): 1514.3 m DRF
Sea floor depth (logger's): 1513.5 m WRF (DIT/APS/HLDS/HNGS main run)
Total penetration: 1697.1 m DRF (m 182.8 DSF)
Total core recovered: 136.17 m (74 % of cored section)
Oldest sediment recovered: Late Cretaceous
Lithologies: Volcanic sediments, bounstone, basaltic breccia, pillow lava and massive flows
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 February 2011.
| Tool string | Pass
|
Top depth (m WMSF) | Bottom depth (m WMSF) | Pipe depth (m WMSF) | Notes |
1.DIT/APS/HLDS/GPIT/HNGS
|
Downlog
|
|
79.5 |
No HLDS/APS |
|
Main
|
80 |
||||
Repeat
|
80 |
||||
2.GBM |
Downlog 1
|
3rd Party tool |
|||
Downlog 2
|
3rd Party tool |
||||
Uplog
|
3rd Party tool |
||||
3.FMS/DSI/GPIT/HNGS
|
Downlog
|
79.5 |
No caliper/images |
||
Main
|
79.5 |
||||
Repeat
|
79.5 |
Hole U1376A was drilled with a 9 7/8" RCB coring bit from sea floor to 1697 m DRF. The hole was filled with sepiolite mud and a wiper trip was completeted prior to logging.
The DIT/APS/HLDS/GPIT/HNGS tool string was run first without any operational problems. The caliper log indicated that the hole was in good conditions, with readings generally between 10 and 11 inches and locally slightly higher than 12 inches.
WHC was used during the logging operations. Ship's heave was about 1 m (peak to peak).
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 (-
1513.5 m). The sea floor depth
was determined by the step in gamma ray values at 1513.5 m WRF on the main run of the DIT/APS/HLDS/GPIT/HNGS tool string. This differs by 0.8 m from the sea floor depth given by the drillers (see
above). The depth-shifted logs have then been depth-matched to the gamma ray log from the main
run of the DIT/APS/HLDS/GPIT/HNGS tool string.
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.
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 the following modes: P&S monopole and upper dipole (standard frequency) in all three runs, and Stoneley mode (standard frequency) in the main run. The velocities were computed from the DTCO (compressional), DTSM (shear) and DTST (Stoneley) logs. The compressional and shear data were fairly weaak in most of the hole. Only in few short intervals did the compressional and shear waves have a relatively high correlation in the slowness time coherency plots.
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.
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). Hole diameter was recorded by the hydraulic caliper on the HLDS
tool (LCAL) and by the FMS tool (C1 and C2); they both indicate good hole conditions. The caliper readings are generally between 10 and 11 inches and locally slightly higher than 12 inches.
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 330.
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