Wireline Standard Data Processing
ODP logging contractor: LDEO-BRG
Location: Okushiri Ridge(Japan Sea)
Latitude: 42.894° N
Longitude: 139.414° E
Logging date: July, 1989
Bottom felt: 2633.8 mbrf (used for depth shift to sea floor)
Total penetration: 464.9 mbsf
Total core recovered: 85.3 m (29 %)
Logging string 1: DIT/SDT/NGT
Logging string 2: FMS/GPIT/NGT (2 passes)
Logging string 3: ACT/GST/NGT
Logging string 4: HLDT/CNTG/NGT (upper and lower sections)
No information available from the ODP Initial Reports about use of wireline heave compensator.
The following bottom-hole assembly/pipe 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/NGT: Bottom-hole assembly at 104.5mbsf
FMS/GPIT/NGT: Bottom-hole assembly at 104.5mbsf
ACT/GST/NGT: Bottom-hole assembly at 104.5mbsf
HLDT/CNTG/NGT: Bottom-hole assembly at 104.5mbsf (upper and lower sections)
DIT/SDT/NGT: Drill pipe at ~ 18 mbsf
FMS/GPIT/NGT: Drill pipe at ~ 18 mbsf
ACT/GST/NGT: Drill pipe at ~ 18 mbsf
HLDT/CNTG/NGT: Drill pipe at ~ 18 mbsf (upper section).
Depth shift: Original logs have been interactively depth shifted with reference to NGT from DIT/SDT/NGT run and to the sea floor (- 2632.5 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 DIT/SDT/NGT logs. 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.
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.
Due to malfunction of the short-spacing HLDT detector, only the bulk density reading from the long spacing detector is considered valid. As a consequence, no valid photoelectric affect (PEF) and density correction (DRHO) curves were recorded.
Data recorded through pipe and/or bottom hole assembly, such as the NGT and CNTG data recorded above 104.5 mbsf, should be used qualitatively only because of the attenuation on the incoming signal. Invalid NGT spikes were recorded at the following depth:
15-21.5, 50-54.5, 83.5-87 and 95-00 mbsf (DIT/SDT/NGT run)
17.5-22, 75-80 mbsf (HLDT/CNTG/NGT run)
17.5-22, 50-51.5, 55-56, 65-66, 89-91 mbsf (ACT/GST/NGT run).
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:
E-mail: Cristina Broglia