Standard Wireline Data Processing
IODP logging
contractor: USIO/LDEO
Hole: U1346A
Expedition: 324
Location: Shatsky Rise - Shirshov Massif
Latitude: 38 ° 00.400 ' N
Longitude: 162°38.710 ' E
Logging date: 18-19 September, 2009
Sea floor
depth (driller's):
3627.4 m DRF
Sea floor
depth (logger's): 3630.9 m WRF
Total
penetration: 3821.8 m DRF
Total core
recovered: 25.73 m (21 % of cored section)
Oldest
sediment recovered:
Early Creataceous
Lithologies:
Calcareous nannofossil oozes, limestones, chert, volcaniclastic turbidites, highly altered basalts.
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 September 2009.
| Tool string | Pass |
Top depth (mbsf) | Bottom depth (mbsf) | Pipe depth (mbsf) | Notes |
1. DIT/APS/HLDS/HNGS
|
Downlog |
117.5 |
Invalid HLDS |
||
Pass 1
|
open hole |
Invalid HLDS |
|||
|
Pass 2
|
117.5 |
Reference |
Logging operations in Hole U1346A took place in rough sea conditions; the heave was generally 4-5 m, with occasional excursions up 6 m. Prior to logging, the hole was conditioned by performing a wiper trip and displacing 38.5 bbl of attapulgite (8.9 ppg). The pipe was set at 3753.5 m DRF. The downlog started at 3559.3 m WRF and stopped at 3777.8 m WRF prior to testing the Wireline Heave Compensator at 3800 m WRF. The caliper on the HLDS tool was kept closed during the descent, therefore no HLDS is valid. The caliper was also kept closed during the short first pass uphole, while the WHC was being tested. A complete dataset was acquired during the second pass uphole, though the logging speed had to be increased to 1,800 ft/hr (usual speed is 900 ft/hr) in order to minimize the chances of the HLDS caliper arm to be damaged by any downward motion caused by the ship's heave. The caliper was closed at 3763 m WRF before entering the pipe.
Depth shift to sea floor and depth match. The original logs were first shifted to the sea floor (- 3630.9 m). The sea floor depth was determined by the step in gamma ray value. This differs by 3.5 m from the sea floor depth given by the drillers (see above). The depth-shifted logs from the downlog have then been depth-matched to the gamma ray log from the Pass 2 of the DIT/HLDS/GPIT/HNGS tool string. Pass 1 did not require any depth matching.
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
HLDS data were corrected for standoff and hole size during the
recording.
High-resolution data. Bulk density (HLDS) data were recorded with a sampling rate 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.
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 or density 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 like the HLDS that require eccentralization and a good contact with the borehole wall. The density log roughly correlates with the resistivity logs, but it is largely affected by the hole conditions. The hole diameter was recorded by the hydraulic caliper on the HLDS
tool (LCAL); it shows a very irregular borehole with intervals exceeding the maximum caliper aperture.
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 324.
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