Wireline Standard Logging Data

ODP logging contractor: LDEO-BRG

Hole: 929E

Leg: 154

Location: Ceara Rise (tropical NW Atlantic)

Latitude: 5° 58.568' N

Longitude: 43° 44.402' W

Logging date: March, 1994

Bottom felt: 4367.5 mbrf (used for depth shift to sea floor)

Total penetration: 808.9 mbsf

Total core recovered: 246.65 m (73.1 %)

Logging Runs

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

Logging string 2: ACT/GST/NGT

Wireline heave compensator was used to counter the mild ship heave. WHC was turned off at ~490 mbsf during the DIT/SDT/HLDT/NGT run due to power failure. WHC was turned off at ~155 mbsf during the ACT/GST/NGT run.

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/HLDT/SDT/NGT: Bottom-hole assembly at ~117 mbsf

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

Processing

Depth shift: For consistency with the core-log correlation performed by the logging scientists onboard using Multi Sensor Track data, this run was first depth-shifted +5 m. Then all original logs have been interactively depth shifted with reference to NGT from DIT/SDT/HLDT/NGT run, and to the sea floor (- 4367.5 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: 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') and short-spacing (3-5-5-7') logs. The data recorded in short spacing mode was of very good quality below 448 mbsf; in the upper part, instead, the long spacingsonic 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.

High-resolution data: 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 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.

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). The caliper closed at about 132 mbsf and therefore no borehole size correction can be performed between this depth and the bottom of the pipe. For this reson, this portion of the data is not included.

Resistivity, acoustic, density, caliper and gamma ray data from upper and lower sections have been spliced at 500 mbsf.

Details of standard shore-based processing procedures are found in the "Explanatory Notes" chapter, ODP IR Volume 154. For further information about the logs, please contact:

Cristina Broglia

Phone: 845-365-8343

Fax: 845-365-3182

E-mail: Cristina Broglia