Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG

Hole: 986D

Leg: 162

Location: Svalbard Margin (Greenland Sea)

Latitude: 77° 20.408' N

Longitude: 9° 4.654' W

Logging date: August, 1995

Bottom felt: 2062.5 mbrf (used for depth shift to sea floor)

Total penetration: 576.8 mbsf

Total core recovered: 241.6 m (41.9 %)

Logging Runs

Logging string 1: DIT/SDT/HLDT/CNTG/NGT (upper and lower sections)

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 ~306 mbsf (upper section)

DIT/SDT/HLDT/CNTG/NGT: Bottom-hole assembly at ~422.5 mbsf (lower section).

Processing

Depth shift: No differential depth shift has been applied as the two sections do not overlap. Original logs have been depth shifted to the sea floor (- 2062.5 m).

Gamma-ray processing: Data have been processed to correct for borehole size and the heavy barite drilling fluid used to stabilize the hole.

Acoustic data processing: The array sonic tool was operated in depth-derived, borehole compensated mode using the long-spacing (8-10-10-12') configuration. The sonic logs from 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.

High-resolution processing: Bulk density and neutron porosity data were recorded at a sampling rate of 2.54 and 5.08 cm respectively. The enhanced bulk density curve is the result of Schlumberger enhanced processing technique performed on the MAXIS system onboard. While in normal processing short-spacing data is smoothed to match the long-spacing one, in enhanced processing this is reversed. In a situation where there is good contact between the HLDT pad and the borehole wall (low density correction) the results are improved, because the short-spacing have better vertical resolution.

Quality Control

null value=-999.25. This value generally 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.

Data recorded through bottom-hole assembly, such as the gamma ray and neutron porosity data above 306 and between 422.5 and 405 mbsf, should be used qualitatively only because of the attenuation on the incoming signal. Invalid gamma ray spikes were recorded at 300-305.5 and 418-422.5 mbsf.

Hole diameter was recorded by the hydraulic caliper on the HLDT tool (CALI).

Details of standard shore-based processing procedures are found in the "Explanatory Notes" chapter, ODP IR Volume 162. For further information about the logs, please contact:

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