Standard Wireline Data Processing
IODP -USIO logging contractor: LDEO-BRG
Hole: U1313B
Expedition: 306
Location: Mid Atlantic Ridge (central N Atlantic)
Latitude: 41° 0.082' N
Longitude: 32°57.438' W
Logging date: March 30-31, 2005
Sea floor depth (driller's): 3424.6 mbrf
Sea floor depth (logger's): 3422.5 mbrf
Total penetration: 302.4 mbsf
Total core recovered: 313 m (103.5 % of cored section)
Oldest sediment cored: Latest Miocene
Lithologies: Nannofossil ooze with varying amounts of foraminifers and clay- to gravel-sized terrigenous components.
The logging data was recorded by Schlumberger in DLIS format. Data were processed at the Borehole Research Group of the Lamont-Doherty Earth Observatory.
| Tool string | Pass | Top depth (mbsf) | Bottom depth (mbsf) | Bit depth (mbsf) | Notes |
| 1. DIT/HLDS/APS//GPIT/HNGS |
Uplog
|
0
|
301
|
65
|
Hole U1313B was logged to the bottom of the hole, and the data are of very good quality. The first time the DIT/HLDS/APS/HNGS/GPIT was lowered into the hole, telemetry kept dropping out for short periods of time. On returning the tool string to the surface, it was found that some water was present at the bottom of the Lamont MGT tool and in the pins of the telemetry cartridge. The MGT was removed and the telemetry cartridge was replaced, and this tool string successfully recorded a main pass to the base of the hole. The wireline heave compensator was used to counter ~2m of ship heave. The Schlumberger heave compensator was then tested for 45 minutes and compensation found to be improved over previous testing. No further logging was performed.
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 match and depth shift to sea floor: The original logs were shifted to the sea floor (-3422.5 m). The sea floor depth was determined by the step in gamma ray values at 3422.5 mbrf. This differs by 2.1 m from the sea floor depth given by the drillers (see above).
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.
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). There is good correlation between the resistivity and density log throughout most of the logged intervals while correlation of the neutron porosity log is generally poor.
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. At Hole U1313B the base of the bottom hole assembly was positioned at 65 mbsf.
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). The hole diameter varies from 10 inches near the base of the hole to 15.5 inches in the upper half of the logged section.
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 306.
For any question about the data or about the LogDB database, please contact LogDB support: logdb@ldeo.columbia.edu.