ODP logging contractor: LDEO-BRG

Well name: 737B

Leg: 119

Location: S Kerguelen Plateau (Antarctic Ocean)

Latitude: 50° 13.67' S

Longitude: 73° 1.95' E

Logging date: January, 1988

Bottom felt: 574.5 mbrf (used for depth shift to sea floor)

Total penetration: 715.5 mbsf

Total core recovered: 298.4 m (41 %)

Logging Runs

Logging string 1: DIT/LSS/GR (upper, middle, and lower sections)

Logging string 2: LDT/CNTG/GPIT/AMS/NGT

Wireline heave compensator was not used to counter ship heave.

Bottom-hole Assembly

The following bottom-hole assembly depths are as they appear on the logs after differential depth shift (see "Depth shift" section) and depth shift to the sea floor. As such, there might be a discrepancy with the original depths given by the drillers onboard. Possible reasons for depth discrepancies are ship heave and drill string and/or wireline stretch.

DIT/LSS/GR: Bottom-hole assembly at ~93 and 295 mbsf

LDT/CNTG/GPIT/AMS/NGT: Bottom-hole assembly at ~296 mbsf.

Processing

Depth shift: Original logs have been interactively depth shifted with reference to NGT from DIT/LSS/GR middle and lower sections and to the sea floor (-574.5 m). The program used is an interactive, graphical depth-match program which allows to visually correlate logs and to define appropriate shifts. The reference and match channels are displayed on the screen, with vectors connecting old (reference curve) and new (match curve) shift depths. The total gamma ray curve (SGR) from the NGT tool run on each logging string is used to correlate the logging runs most often. In general, the reference curve is chosen on the basis of constant, low cable tension and high cable speed (tools run at faster speeds are less likely to stick and are less susceptible to data degradation caused by ship heave). Other factors, however, such as the length of the logged interval, the presence of drill pipe, and the statistical quality of the collected data (better statistics is obtained at lower logging speeds) are also considered in the selection. A list of the amount of differential depth shifts applied at this hole is available upon request.

Gamma-ray processing: NGT data have been processed to correct for borehole size and type of drilling fluid.

Acoustic data processing: The long spacing sonic logs have been processed to eliminate some of the noise and cycle skipping experienced during the recording. The data has been spliced at 415 mbsf; no data was recorded in the 260-308 mbsf interval. Using two sets of the four transit time measurements and proper depth justification, four independent measurements over a -2ft interval centered on the depth of interest are determined, each based on the difference between a pair of transmitters and receivers. The program discards any transit time that is negative or falls outside a range of meaningful values selected by the processor.

Quality Control

null value=-999.25. This value may replace recorded log values or results which are considered invalid (ex. processed sonic data).

During the processing, quality control of the data is mainly performed by cross-correlation of all logging data. Large (>12") and/or irregular borehole affects most recordings, particularly those that require eccentralization (CNTG, LDT) and a good contact with the borehole wall. Because barite mud was used to condition the hole before lowering the LDT/CNTG/GPIT/AMS/NGT tool string and because the heavy barite always tend to concentrate in the bottom part of the hole after circulation stops, the density and photoelectric effect readings increase gradually towards the bottom of the hole; this effect is particularly evident below 550 mbsf.

Data recorded through bottom-hole assembly should be used qualitatively only because of the attenuation on the incoming signal.

Hole diameter was recorded by the 3-arm mechanical caliper device; constant values were recorded in the upper part of the hole, which indicate that the caliper arms were probably fully open over a washed-out section.

The data from the DIT/LSS/GR runs has been spliced as follows:

resistivity: at 430 mbsf

gamma ray: at 425 mbsf

caliper: at 405 mbsf

sonic: at 415 mbsf.

Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP IR volume 119. For further questions about the logs, please contact:

Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia