Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG

Hole: 1061A

Leg: 172

Location: Blake Ridge (NW Atlantic)

Latitude: 29° 58.4976' N

Longitude: 73° 35.9929' W

Logging date: March, 1997

Bottom felt: 4048.2 mbrf

Total penetration: 350.3 mbsf

Total core recovered: 298.2 m (85.1 %)

Logging Runs

Logging string 1: DIT/HLDT/APS/HNGS

Logging string 2: FMS/GPIT/SDT/NGT (2 passes)

Wireline heave compensator was used to counter ship heave during the DIT/HLDT/APS/HNGS pass and during pass 2 of the FMS/GPIT/SDT/NGT.

Bottom-hole Assembly/Pipe

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/APS/HNGS: Bottom-hole assembly at ~88 mbsf

FMS/GPIT/SDT/NGT: Bottom-hole assembly at ~88 mbsf (pass 1)

FMS/GPIT/SDT/NGT: Recorded open-hole

DIT/HLDT/APS/HNGS: Drill pipe at ~27 mbsf.

Processing

Depth shift: Original logs have been interactively depth shifted with reference to NGT from FMS/GPIT/SDT/NGT pass 1 and to the sea floor (- 4046.5 m). This value corresponds to the sea bottom depth as observed on the logs and differs 1.7 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 and HSGR) 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: NGT data from the FMS/GPIT/SDT/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. Because of the extremely low quality of the sonic logs, no processing from the transit times can be performed. Sonic waveform processing is necessary to obtain meaningful results.

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 has better vertical resolution.

Quality Control

null value=-999.25. This value generally may replace invalid log values.

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.

The deep resistivity reading (IDPH) from the phasor dual induction tool is invalid; it has been replaced by the deep dual induction curve (ILD).

Invalid photoelectric effect spikes were recorded at 168 and 191 mbsf.

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 172. For further questions about the logs, please contact:

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