Standard Wireline Data Processing
IODP logging contractor: USIO/LDEO
Hole: U1337A
Expedition: 321
Location: Equatorial Pacific Sediment Mound (NE Equatorial Pacific)
Latitude: 3° 50.009 ' N
Longitude: 123°12.352 ' W
Logging date: May 23-25, 2009
Sea floor depth (driller's): 4472 m DRF
Sea floor depth (logger's): 4442.5 m WRF (DIT/HLDS/GPIT/HNGS)
Sea floor depth (logger's): 4474 m WRF (VSI/SGT)
Sea floor depth (logger's): 4467 m WRF (FMS/DSI/GPIT/HNGS)
Total penetration: 449.8 m DSF
Total core recovered: 421.39 m (94 % of cored section)
Oldest sediment recovered: Uppermost Oligocene
Lithology: Carbonate muds, nannofossil oozes, diatom oozes, laminated and bioturbated muds.
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 May 2009.
Tool string | Pass | Top depth (mbsf) | Bottom depth (mbsf) | Pipe depth (mbsf) | Notes |
1.DIT/HLDS/GPIT/HNGS
|
Downlog |
76 |
No valid HLDS |
||
Pass 1
|
open hole |
||||
Pass 2
|
77.5 |
||||
2. VSI/SGT
|
Downlog
|
||||
Upper
|
|||||
Lower
|
|||||
3. FMS/DSI/GPIT/HNGS |
Pass 1
|
open hole |
|||
Pass 2 |
77 |
Reference |
Three tool strings were used at Hole U1337A. Prior to logging, the hole was swept with ~9 ppg sepiolite/attapulgite mud, followed by a wiper trip. After pumping a go-devil through the drill string to open the lockable flapper valve, the hole was displaced with ~10 ppg barite/attapulgite mud. During logging with the DIT/HLDS/GPIT/HNGS tool string, the Schlumberger engineer noted that one of the wheels in the depth measuring mechanism off the wireline winch was broken, possibly affecting the depth measurement. In fact, this resulted in the sea floor being detected by the DIT/HLDS/GPIT/HNGS
tool string at a depth that is more than 15 m higher than the one detected by the remaining tool strings (see depth shifts, below).
Due to daylight requirements, the VSI/SGT tool string was run next. Nine stations were taken until a hose in the wireline heave compensator burst, releasing a large amount of hydraulic fluid. Due to the favorable weather conditions (1m peak-to trough waves), shooting was resumed, with repair of the WHC postponed to the rig-up of the last tool string. A total of 16 stations were acquired with the VSI; three additional shallow stations were attempted in soft sediments but failed, due to lack of coupling of the VSI to the borehole wall.
The FMS/DSI/GPIT/HNGS tool string run was uneventful, with further tests of the WHC conducted.
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. Due to the breakage in the depth measuring mechanism (see above), different values were used to depth shift the original logs to the sea floor. The sea floor depth was determined by the step in gamma ray values: 4442.5 m WRF for the three passes of the DIT/HLDS/GPIT/HNGS tool string. 4467 m WRF for the two passes of the FMS/DSI/GPIT/HNGS tool string and 4474 m WRF for the downlog and lower section of the VSI/SGT and 4472.5 m WRF for the upper section of the VSI/SGT tool string. These values differ differs by 2 to 29.5 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 Pass 2 of the FMS/DSI/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
and SGT data were corrected for hole size during the recording. The HLDS data were corrected for hole size during the
recording.
High-resolution
data. Bulk density
(HLDS) data were recorded with 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.
No high resolution data were recorded with the SGT tool.
Acoustic
data. The dipole shear
sonic imager (DSI) was operated in P&S monopole and upper dipole modes during both passes. The velocities were computed from the DTCO (monopole mode) and DT2 (upper dipole mode) delay times. They data display good repeatability between the two passes, with good data below 235 m (WMSF).
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
(HLDS). Hole diameter was recorded by the hydraulic caliper on the HLDS
tool (LCAL) and by the FMS tool (C1 and C2). The FMS caliper from the two passes shows remarkable repeatibility, in a circular hole that becomes elliptical below 280 m (WMSF), with values in the 11-15 inch range. On the other hand, though similar in shape, the HLDS caliper is consistently higher, with values mostly in the 14-19 inch range.
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 321.
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