Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG

Hole: 1093D

Leg: 177

Location: Shona Ridge (Antarctic Ocean)

Latitude: 49° 58.5907' S

Longitude: 5° 51.9338' E

Logging date: January, 1998

Bottom felt: 3635 mbrf

Total penetration: 597.7 mbsf

Total core recovered: 160.4 m (34.7 %)

Logging Runs

Logging string 1: DIT/APS/HLDS/HNGS

Logging string 2: GHMT/NGT (2 passes)

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/APS/HLDS/HNGS: Bottom-hole assembly at ~65 mbsf

GHMT/NGT: Recorded open-hole (both passes).

Processing

Depth shift: Original logs have been interactively depth shifted with reference to HNGS from DIT/APS/HLDS/HNGS run and to the sea floor (- 3637.5 m). This value corresponds to the sea floor depth shown on the DIT/APS/HLDS/HNGS logs and differs 2.5 m from the "bottom felt" depth given by the drillers. 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 or HNGS) from the NGT or HNGS 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: The HNGS data have been corrected in real time for borehole size and type of drilling fluid during the recording. The NGT data have been corrected for borehole size and type of drilling fluid during the processing.

High-resolution data: Neutron porosity data were recorded at a sampling rate of 5.08 cm in addition to the standard 15.24 cm sampling rate.

Geological Magnetic Tool: The Geological Magnetic Tool collected data at two different sampling rates, the standard 15.24 cm and 5.08 cm rate. Both data sets have been depth shifted to the reference run and to the sea floor.

Quality Control

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

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 (APS/HLDS) and a good contact with the borehole wall. Caliper readings show the hole to be more than 18 inches over most of the logged interval; because of the lack of proper contact with the borehole wall both density and porosity readings are of extremely poor quality and are not presented.

Data recorded through bottom-hole assembly, such as the HNGS data above 65 mbsf, should be used qualitatively only because of the attenuation on the incoming signal.

Hole diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL).

Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP IR volume 177. For further questions about the logs, please contact:

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