Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG

Hole: 735B

Leg: 118

Location: SW Indian Ridge (SW Indian Ocean)

Latitude: 32° 43.395' S

Longitude: 57° 15.959' E

Logging date: December, 1987

Water depth (as seen on logs): 731 mbrf

Total penetration: 500.7 mbsf

Total core recovered: 434.8 m (86.8 %)

Logging Runs

Logging string 1: DIT/LSS/GR. Due to an electrical short in the cable head, no resistivity or caliper data could be recorded. Also, due to the low amplitude of the compressional waves, the Schlumberger software was unable to pick reliable arrival times.

Logging string 2: LDT/CNTG/GPIT/NGT

Logging string 3: ACT/GST/GPIT/NGT (2 passes)

Logging string 4: DIT/GR

Logging string 5: DLL

Logging string 6: Multichannel Sonic tool (MCS)

Wireline heave compensator was used to counter ship heave; waves were 8-12 ft high.

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/or wireline stretch.

LDT/CNTG/GPIT/NGT: Bottom-hole assembly at ~25 mbsf

ACT/GST/GPIT/NGT: Bottom-hole assembly at ~23 mbsf

DIT: Bottom-hole assembly at ~42 mbsf

DLL: Bottom-hole assembly at ~45 mbsf.

Processing

Depth shift: Original logs have been interactively depth shifted with reference to NGT from LDT/CNTG/GPIT/NGT run and to the sea floor (- 731 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 from the LDT/CNTG/GPIT/NGT and ACT/GST/GPIT/NGT (pass 1) run have been processed to correct for borehole size and type of drilling fluid.

Quality Control

null value=-999.25. This value generally appears in discrete core measurement files and also it 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, HLDT) and a good contact with the borehole wall.

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 (MCD) during the second pass of the DIT tool string.

Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP IR volume 118. For further questions about the logs, please contact:

Cristina Broglia

Phone: 845-365-8343

Fax: 845-365-3182

E-mail: Cristina Broglia