Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG

Well name: 762C

Leg: 122

Location: Exmouth Plateau (SE tropical Indian Ocean)

Latitude: 19¡ 53.23' S

Longitude: 112¡ 15.24' E

Logging date: August, 1988

Bottom felt: 1371.4 mbrf (used for depth shift to sea floor)

Total penetration: 940 mbsf

Total core recovered: 534.6 m (69 %)

Logging Runs

Logging string 1: DIT/SDT/NGT

Logging string 2: ACT/GST/NGT

Logging string 3: LDT/CNTG/NGT

There are no information in the logging report from this hole about use of the wireline heave compensator to counter ship heave.

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.

DIT/SDT/NGT: recorded open-hole, with the exception of the 222.5-241 mbsf interval, which was recorded through pipe

ACT/GST/NGT: recorded open-hole

LDT/CNTG/NGT: bottom hole assembly at ~155 mbsf.

Processing

Depth shift: Original logs have been interactively depth shifted with reference to NGT from ACT/GST/NGT run and to the sea floor (- 1371.4 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 the presence of bottom-hole assembly, drill pipe, and type of drilling fluid.

Acoustic data processing: The array sonic tool was operated in standard depth-derived borehole compensated mode, including long-spacing (8-10-10-12') logs. The sonic logs have been processed to eliminate some of the noise and cycle skipping experienced during the recording. 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 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. Large (>12") and/or irregular borehole affects most recordings, particularly those that require eccentralization (LDT) and a good contact with the borehole wall.

Due to malfunction of the CNTG tool, no data is included in the database. Also, no spherically-focused resistivity (SFLU) data was recorded.

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.

Data form the upper and lower sections of the DIT/SDT/NGT have been spliced as follows:

resistivity: 350 mbsf

acoustic: 330 mbsf

gamma ray: 350 mbsf

caliper: 350 mbsf.

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