Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG

Well name: 760B

Leg: 122

Location: Exmouth Plateau (tropical SE Indian Ocean)

Latitude: 16° 55.32' S

Longitude: 115° 32.48' E

Logging date: July, 1988

Bottom felt: 1981.1 mbrf (used for depth shift to sea floor)

Total penetration: 506 mbsf

Total core recovered: 132 m (24 %)

Logging Runs

Logging string 1: DIT/SDT/NGT (1 pass)

Logging string 2: DIT/SDT/CNTG/NGT (2 main and 1 repeat. Main #2 recorded completely through pipe).

Due to the excellent sea conditions, the wireline heave compensator was not used.

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, use of wireline heave compensator, and drill string and/or wireline stretch.

DIT/SDT/NGT: Bottom-hole assembly at ~ 63 mbsf (.

DIT/SDT/CNTG/NGT: Bottom-hole assembly at ~ 63 mbsf (Main # 2 recorded through pipe).

Processing

Depth shift: Original logs have been depth shifted to the sea floor (- 1981 m).

Gamma-ray processing: Because the spectral windows necessary for gamma ray correction were not part of the original data set, no correction for borehole size and type of drilling fluid has been performed.

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

NOTE: The processed data come from DIT/SDT/CNTG/NGT first pass.

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) 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. An invalid spike has been recorded at ~ 28 mbsf.

Hole diameter was recorded by the 3-arm mechanical caliper device.

Additional information about Hole 760B logs can be found in the Site Report, ODP IR Volume 122. For further information about the logs, please contact:

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