Wireline Standard Data Processing

 

ODP logging contractor: LDEO-BRG

Hole: 883F

Leg: 145

Location: Detroit Sea Mount (NW Pacific)

Latitude: 51° 11.906' N

Longitude: 167° 46.085' E

Logging date: August, 1992

Bottom felt: 2396.5 mbrf (used for depth shift to sea floor)

Total penetration: 894.4 mbsf

Total core recovered: 13.6 m (46.2 %)

 

Logging Runs

 

Logging string 1: ACT/GST/NGT

Logging string 2: NMRT (2 passes)

Logging string 3: SUMT (2 passes)

Logging string 4: FMS/GPIT/NGT (4 passes)

Logging string 5: DIT/HLDT/SDT/CNT/NGT

     

Wireline heave compensator was used to counter ship heave resulting from the mild sea conditions.

 

Bottom-hole Assembly

 

The following bottom-hole assembly depths are as they appear on the logs after differential depth shift (see ˝Depth shiftţ 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.

     

ACT/GST/NGT: Bottom-hole assembly at ~120 mbsf

FMS/GPIT/NGT: Bottom-hole assembly at ~120 mbsf

DIT/SDT/HLDT/CNTG/NGT: Bottom-hole assembly at ~96 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 (- 2936.5 m). 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 array sonic tool was operated in standard depth-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.

 

Resistivity Processing: As a test, the resistivity data have been corrected for borehole size, type of drilling fluid, temperature, and standoff. As expected, the corrections were negligible and they have not been performed at any of the other holes logged during this leg.

 

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. 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.

 

The hydraulic caliper on the HLDT tool (CALI) failed to open, thus affecting the recording of the density data. In fact, in order to provide good data, the tool is supposed to run in contact with the borehole wall, a condition obtained by means of a hydraulic arm that also measures the hole diameter. Additional measurements are provided by the caliper recorded by the FMS string (C1 and C2).

     

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

 

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

 

Cristina Broglia

Phone: 845-365-8343

Fax: 845-365-3182

E-mail: Cristina Broglia