Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG

Hole: 881C

Leg: 145

Location: (NW Pacific)

Latitude: 47° 6.133' N

Longitude: 161° 29.490' E

Logging date: August, 1992

Bottom felt: 5541.7 mbrf

Total penetration: 363.8 mbsf

Total core recovered: 227.2 m (62.5 %)

Logging Runs

Logging string 1: DIT/SDT/HLDT/CNT/NGT (3 passes)

Additional descents with the Formation Microscanner and geochemical string were unsuccessful.

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/CNTG/NGT: Bottom-hole assembly at ~46 mbsf (pass 1)

DIT/SDT/HLDT/CNTG/NGT: Bottom-hole assembly at ~45 mbsf (pass 2)

DIT/SDT/HLDT/CNTG/NGT: Bottom-hole assembly at ~45 mbsf (pass 3).

Processing

Depth shift: Original logs have been interactively depth shifted with reference to NGT from DIT/SDT/HLDT/CNTG/NGT pass 3 and to the sea floor (- 5552 m). The data has been shifted 5552 m instead of 5541.7 m (drillers' sea floor) in order to match a lithologic boundary at 164 mbsf. 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 borehole size and type of drilling fluid.

Acoustic data processing: Because of the good quality of the sonic logs, no processing has been performed.

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. The lithodensity tool (HLDT) took a serious bend, due to ship heave, during the first run; caliper and density data are therefore questionable. No borehole size correction could be applied to the density log during the recording of pass 2 and 3, therefore the data is of low quality. The density curve included in the database is a combination of run 1 (upper part) and run 3 (lower part) logs, spliced at ~ 236.5 mbsf. The neutron log is also of poor quality, due to the lack of eccentralization and the high porosity of the formation.

The spherically focused log (SFL) failed during pass 1.

Data recorded through bottom-hole assembly should be used qualitatively only because of the attenuation on the incoming signal.

Hole diameter was initially recorded by the hydraulic caliper on the HLDT tool (CALI); soon after the beginning of the recording downhole the caliper began reading high values that exceeded 18.5 inches. When the tool string was recovered, it was noted that the caliper arm had been bent upward.

Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP IR volume 145. For further questions about the logs, please contact:

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