Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG

Well name: 764B

Leg: 122

Location: Exmouth Plateau (tropical SE Indian Ocean)

Latitude: 16° 33.96' S

Longitude: 115° 27.43' E

Logging date: August, 1988

Bottom felt: 2710 mbrf (used for depth shift to sea floor)

Total penetration: 294.5 mbsf

Total core recovered: 44.3 m (17 %)

Logging Runs

Logging string 1: ACT/GST/NGT

Logging string 2: LDT/CNTG/NGT (Note: the LDT is a pad device than must be used in open holes only as the data is recorded while the pad is pressed against the borehole wall. The density data recorded in Hole 764B is therefore invalid).

No information available about use of wireline heave compensator.

Bottom-hole Assembly/Pipe

The following bottom-hole assembly and drill pipe 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.

ACT/GST/NGT: recorded through bottom hole assembly up to ~ 201 mbsf

ACT/GST/NGT: recorded through drill pipe up to mudline

LDT/CNTG/NGT: recorded through bottom hole assembly up to ~ 201 mbsf

LDT/CNTG/NGT: recorded through drill pipe up to mudline.

Processing

Depth shift: Original logs have been interactively depth shifted with reference to NGT from ACT/GST/NGT run and to the sea floor (- 2710 m). Correlation between these two runs is generally poor, because of the presence of pipe and because the formation was radioactively activated during the recording of the LDT/CNT/NGT. 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 from the ACT/GST/NGT run have been processed to correct for the presence of bottom-hole assembly, drill pipe, and type of drilling fluid. Due to drill pipe movement during the recording in the 20-27 and 96-102 mbsf intervals, the data is not valid.

Quality Control

null value=-999.25. This value generally appears in discrete core measurement files and also it may replace invalid log values or results (ex. processed sonic data).

During the processing, quality control of the data is mainly performed by cross-correlation of all logging data. All data recorded at Hole 764B were acquired through pipe and bottom hole assembly and therefore they were greatly attenuated; in addition, the geochemical data, and in particular the iron elemental yield, were affected by the iron present in the drill pipe. These effects were in great part removed during the processing, however it is recommended to use the data qualitatively only. Invalid geochemical data were acquired in the 20-27 and 96-102 mbsf intervals, due to pipe movement during the recording.

Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP IR volume 122. For further questions about the logs, please contact:

Cristina Broglia

Phone: 845-365-8343

Fax: 845-365-3182

E-mail: Cristina Broglia