Standard Wireline Data Processing
(re-netry Phase 3)
ODP logging contractor: LDEO-BRG
Hole: 1256D, re-entry (Logging Phase 3)
Expedition: 312
Location: Guatemala Basin (NE equatorial Pacific)
Latitude: 6° 44.163' N
Longitude: 91° 56.061' W
Logging date: December 20-23, 2005
Sea floor depth (driller's): 3645.4 mbrf
Sea floor depth (logger's): 3643.5 mbrf
Total penetration: 1507.1 mbsf
Total core recovered: 252 m
(18.5 % of cored section)
Oldest sediment recovered: Calcareous nannofossil ooze (Middle Miocene) at Hole 1256B during ODP
Leg 206
Lithologies: Clay-rich sediments and calcareous nannofossil ooze (sediments); basalt and gabbro (basement)
The logging data was recorded by Schlumberger in DLIS
format. Data were processed at the Borehole Research Group at the
Lamont-Doherty Earth Observatory.
| Tool string | Pass | Top depth (mbsf) | Bottom depth (mbsf) | Pipe depth (mbsf) | Notes |
| 1.DLL/APS/HLDS/HNGS/TAP |
Main |
272 |
1429 |
285 |
Reference log, DLL failed |
| Repeat |
1085 |
1428 |
DLL failed |
||
| 2. VSI |
1426 |
60 stations, at 22 m intervals |
|||
| 3. FMS/DSI/GPIT/SGT |
Failed |
||||
| 4. UBI/DSI/GPIT/SGT |
Pass 1 Main |
1072 |
1433 |
||
| Pass 1 Repeat |
1298 |
1436 |
|||
| Pass 2 |
1064 |
1408 |
Schlumberger *WHC used |
||
| 5. FMS/GPIT/SGT |
Pass 1 |
1098 |
1435 |
||
| Pass 2 |
1102 |
1436 |
|||
| 6. DLL/EMS/SGT/TAP |
Downlog |
305 |
1419 |
||
| Main | 251 |
1432 |
283 |
Hole 1256D, was drilled during Leg
206 to 752 mbsf and during Expedition 309 to 1255 mbsf. Logging to 1220 mbsf
was conducted in 2 phases during Expedition 309: Phase 1 before deepening the
hole and Phase 2 after reaching a total depth of 1255 mbsf. Phase 3 logging of
Hole 1256D was conducted at the end of Expedition 312, after reaching a total
depth of 1507.1 mbsf. The first tool string, DLL/APS/HLDS/HNGS/TAP, reached to
within 70 m of the bottom of the hole. The VSI was run second, because of the
need to run the checkshot survey during the daylight hours. The deepest station
showed a lot of noise, but the second station 50 m above showed better signals.
A FMS/DSI/GPIT/SGT tool string was then attempted, but soon after starting to
log the FMS failed and telemetry was lost, so the tool string was brought back
to the surface. Next, the UBI/DSI/GPIT/SGT tool string collected good logs and
images. The Schlumberger heave compensator was used for Pass 2 (the Lamont
heave compensator was used for all other runs). The FMS cartridge was replaced
for the FMS/GPIT/SGT tool string; it recorded good images. The DLL/EMS/SGT tool
string was run last in order to obtain the resistivity logs that were not
collected by the DLL/APS/HLDS/HNGS/TAP tool string because of DLL failure.
The depths in the table are for the processed logs (after
depth matching between passes and depth shift to the sea floor). 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 the
'bottom felt' depth in soft sediment.
Depth shift: The original logs were first shifted to the sea
floor (-3643.5 m), and then the LCAL and HSGR logs from the
DLL/APS/HLDS/HNGS/TAP main run were depth matched to the equivalent logs from
phase 1 and 2 logging of this hole. This shifted main pass became the reference
for the other tool strings from phase 3 logging. The sea floor depth was not
determined directly; the sea floor depth was set so that the bottom of the
casing in the logs appeared at the same depth (269m) as given by the drillers,
as had been done for the phase 1 and 2 logging. For Hole 1256D, it differs by 1.9 m from the "bottom
felt" depth given by the drillers (see above).
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 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 SGT data were corrected for hole size
during the recording. The APS and HLDS have been corrected for standoff and
hole diameter respectively during the recording.
High-resolution data: Bulk density and neutron porosity data were
recorded at a sampling rate of 2.54 and 5.08 cm, respectively. 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. SGT gamma ray was recorded at
15.24 and 5.08 cm sampling rates.
Acoustic data: The dipole shear sonic imager (DSI) was run in
monopole P&S, upper and lower dipole, and Stoneley modes on Pass 1 and in
monopole P&S, Stoneley, and cross dipole on Pass 2. The monopole
compressional and shear waveform data have been processed post-cruise. The
online files include both processed (VCO and VS) and original velocities (VS1,
VS2, and VST).
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 density log).
Gamma ray logs recorded through bottom hole assembly (BHA)
and drill pipe should be used only qualitatively, because of the attenuation on
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 (HLDS/APS). Hole
diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL) and on
the FMS tool (C1 and C2). The newly drilled part of the hole was in very good
condition, generally reading between 10 inches in diameter, with one wider
section at 1298-1307 mbsf.
A null value of -999.25 may replace invalid log values.
Additional information about the drilling and logging operation
can be found in the Operations section of the Site Chapter in IODP Expedition
Reports Volume 312. For further questions about the logs, please contact:
Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia