Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG

Hole: 1052E

Leg: 171B

Location: Blake Nose (NW Atlantic Ocean)

Latitude: 29° 57.0794' N

Longitude: 76° 37.609' W

Logging date: February, 1997

Bottom felt: 1355 mbrf

Total penetration: 684.8 mbsf

Total core recovered: 544.8 m (60.2 %)

Logging Runs

Logging string 1: DIT/HLDT/APS/HNGS

Logging string 2: FMS/SDT/GPIT/NGT (main and repeat)

Logging string 3: GHMT/NGT (main)

Wireline heave compensator was not available on Leg 171B. Sea state conditions were moderate, with sea swells in the order of 1 m, with no obvious effects on the logging data.

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 and drill string and/or wireline stretch.

DIT/APS/HLDT/NGT: Bottom-hole assembly at ~222 mbsf

FMS/SDT/GPIT/NGT: Bottom-hole assembly at ~222 mbsf

GHMT/NGT: Bottom-hole assembly at ~222 mbsf.

Processing

Depth shift: Original logs have been interactively depth shifted with reference to NGT from DIT/APS/HLDT/NGT run and to the sea floor (- 1353 m). The amount of depth shift to the sea floor corresponds to the water depth as seen on the logs and differs 2 m from the drillers' "bottom felt" depth. 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 from the FMS/GPIT/SDT/NGT and GHMT/NGT runs have been processed to correct for borehole size and type of drilling fluid. HNGS data from the DIT/APS/HLDT/HNGS tool string were corrected in real-time during the recording.

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 quality of the former is quite poor and the data has not been processed. The latter exhibits better quality data, with the exception of the TT2 channel (3' spacing), which shows some offset in the upper part of the hole. For this reason, the data has not been processed and velocity has been computed directly form the DTL (long spacing)

Geological Magnetic Tool: The Geological Magnetic Tool collected data at two different sampling rates, the standard 0.1524 m rate and 0.0508 m. Both data sets have been depth shifted to the reference run and to the sea floor. Full processing of the magnetic data will be performed at a later date by the Institute Mediterraneen de Technologie (Marseilles, France).

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 (APS, 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.

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) and on the FMS string (C1 and C2).

Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP IR volume 171B. For further questions about the logs, please contact:

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