Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG

Hole: 843A

Leg: 136

Location: Hawaiian Arch (central tropical N Pacific)

Latitude: 19° 20.53' N

Longitude: 159° 5.68' W

Logging date: March, 1991

Bottom felt: 4422.5 mbrf (used for depth shift to sea floor)

Total penetration: 237.7 mbsf

Total core recovered: 4 m (1.7 %)

Logging Runs

Logging string 1: DIT/SDT/HLDT/NGT (2 passes)

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

DIT/SDT/HLDT/NGT: Bottom-hole assembly at ~50 mbsf (pass 1)

DIT/SDT/HLDT/NGT: Recorded open-hole (pass 2).

Processing

Depth shift: The comparison between the resistivity curves from the two passes shows that boh runs were affected by cable pulls during the recording and that the tool was frequently stuck in the hole. For this reason, neither run has been selected for differential depth shift. All data has been depth shifted to the sea floor (- 4422.5 m).

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

Acoustic data processing: The SDT was run in depth-derived, borehole compensated mode. The long-spacing (8-10-10-12') sonic logs from both runs 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 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 (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 hydraulic caliper on the HLDT tool (CALI). Invalid density spikes were recorded at 66-74, 101, 205, and 207 mbsf (pass 1) and 62-63, 106, 111, and 117 mbsf (pass 2).

Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP IR volume 136. For further questions about the logs, please contact:

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