Wireline Standard Data Processing
ODP logging contractor: LDEO-BRG
Location: Ontong-Java Plateau (tropical NW Pacific Ocean)
Latitude: 0° 19.11' N
Longitude: 159° 21.69' E
Logging date: February, 1990
Bottom felt: 2531 mbrf (used for depth shift to sea floor)
Total penetration: 743.1 mbsf
Total core recovered: 666.4 m (89 %)
Logging string 1: DIT/SDT/NGT
Logging string 2: ACT/GST/HLDT/NGT (upper and lower sections)
Wireline heave compensator was used to counter ship heave; seas were calm.
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/NGT: Bottom-hole assembly at ~90 mbsf
ACT/GST/HLDT/NGT: Bottom-hole assembly at 90 mbsf.
Depth shift: Because of the low signature of the NGT logs (< 10 API units) and the uniformity of the lithologies encountered, no depth match between runs is possible. The original logs have been depth shifted to the sea floor (- 2531 m).
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-derived borehole compensated mode, including long-spacing (8-10-10-12') logs. The sonic logs are of excellent quality and do not need processing; compressional velocity has been computed from the delay times.
null value=-999.25. This 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 (HLDT) and a good contact with the borehole wall. The HLDT is particularly affected by the large hole in the 290-320 mbsf interval; more low-density readings in the 180-290 mbsf intervals are also he result of poor 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) by the 3-arm Mechanical Caliper Device (MCD); the HLDT caliper reached its maximum extension (18 inches) above 350 mbsf, thus giving little information about the true conditions of the hole.
E-mail: Cristina Broglia
<![if !supportEmptyParas]> <![endif]>