Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG

Hole: 797C

Leg: 127

Location: Yamato Basin (Japan Sea)

Latitude: 38.616°N

Longitude: 134.536° E

Logging date: August, 1989

Bottom felt: 2876 mbrf

Total penetration: 900.1 mbsf

Total core recovered: 164.2 m (39 %)

Logging Runs

Logging string 1: DIT/SDT/HLDT/CNTG/NGT

Logging string 2: FMS/GPIT/NGT (3 passes)

Logging string 3: ACT/GST/NGT

No information is available from the ODP Initial Reports about use of wireline heave compensator.

Bottom-hole Assembly/Pipe/Casing

The following bottom-hole assembly/pipe/casing 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/HLDT/CNTG/NGT: Bottom-hole assembly at mbsf

ACT/GST/NGT: Bottom hole assembly at ~630 mbsf

FMS/GPIT/NGT: Bottom-hole assembly at mbsf (pass 1)

FMS/GPIT/NGT: Bottom-hole assembly at mbsf (pass 1)

ACT/GST/NGT: Drill pipe at~520 mbsf

Casing shoe at ~81 mbsf.

Processing

Depth shift: Original logs have been interactively depth shifted with reference to NGT from DIT/SDT/HLDT/CNTG/NGT run and to the sea floor (- 2875 m). The amount of depth shift applied differs from the "bottom felt" depth (see above) given by the drillers; it corresponds to the depth of the sea floor observed on the ACT/GST//NGT logs. No differential depth shift could be applied to the FMS/GPIT/NGT runs 2 and 3 due to lack of good correlation with the reference run. 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: The SDT 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.

The interval between 370 and 385 mbsf remains of very poor quality even after processing; a detailed explanation of the reasons that induced the noise is given in the Leg 128 Initial Reports volume, page 393.

Quality Control

null value=-999.25. This value may replace invalid recorded log values or results.

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. Hole deviation can also affect the data negatively; the FMS, for example, is not designed to be run in holes deviated more than 10 degrees, as the tool weight might cause the caliper to close.

Data recorded through bottom-hole assembly should be used qualitatively only because of the attenuation on the incoming signal. This is the case of the geochemical data that were recorded through bottom holes assembly, pipe, and casing and of the NGT data recorded thorough casing above 81 mbsf. Invalid gamma ray data spikes were recorded at 72.5 mbsf (DIT/SDT/HLDT/CNTG/NGT string) and 57.5, 546,-549, 557.5, 559.5, 567, 585, 594, 596, 602, and 605 mbsf (ACT/GST/NGT string).

The lithodensity (HLDT) tool did not record any valid data due to malfunction of the circuits used to count electrons at various energy levels.

Hole diameter was recorded by the hydraulic caliper on the HLDT tool (CALI) and on the FMS string (C1 and C2).

Hole diameter was recorded by the hydraulic caliper on the HLDT tool (CALI),and the caliper on the FMS string (C1 and C2).

Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP IR volume 127-128. For further questions about the logs, please contact:

Cristina Broglia

Phone: 845-365-8343

Fax: 845-365-3182

E-mail: Cristina Broglia