Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG

Hole: 1263A

Leg: 208

Location: Walvis Ridge (tropical SE Atlantic)

Latitude: 28° 31.970' S

Longitude: 2° 46.769' E

Logging date: April 1, 2003

Bottom felt: 2728.2 mbrf

Total penetration: 345.6 mbsf

Total core recovered: 295.8 m (85.6 %)

Logging Runs

Logging string 1: DIT/APS/HLDS/HNGS/TAP/MGT

Logging string 2: FMS/DSI/GPIT/SGT

The DIT/APS/HLDS/HNGS/TAP/MGT tool string reached the bottom of the hole. The lockable flapper valve, however, was not latched open and the tools string re-entered the pipe only after pumping water through the pipe for some time. The MGT run was cancelled. A first attempt at the FMS/DSI/GPIT/SGT run was blocked just outside the pipe; after running a wiper trip the tool string was run into the hole again, reaching a blockage at174 mbsf. Logs were taken from that point. The wireline heave compensator was used to counter ship heave.

Bottom Hole Assembly

The following bottom hole assembly (BHA) 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. Typical reasons for depth discrepancies are ship heave, use of wireline heave compensator, and drill string and/or wireline stretch.

DIT/APS/HLDS/HNGS/TAP/MGT: bottom hole assembly at ~85 mbsf

FMS/DSI/GPIT/SGT: bottom hole assembly at ~90 mbsf

Processing

Depth shift: No unambiguous depth match of the gamma radiation, caliper, resistivity or sonic logs could be found between the runs; therefore, the logs were just block-shifted to the sea floor (-2727 m). The seafloor depth was based on the step in gamma radiation observed on the DIT/APS/HLDS/HNGS/TAP/MGT HSGR log. The seafloor depth differs by 1.2 m from the seafloor depth determined by the drillers..

Environmental corrections: The HNGS and SGT data were corrected for hole size during the recording. The APS and HLDS have been corrected for standoff and hole diameter respectively during the recording.

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 HLDS pad and the borehole wall (low-density correction) the results are improved, because the short spacing has better vertical resolution. SGT gamma ray was recorded at 15.24 and 5.08 cm sampling rates.

Sonic data: The DSI tool was run in P&S monopole, lower dipole, and first motion detection modes. No usable shear data were obtained. The two compressional wave velocities from the monopole and FMD modes logs match over some intervals, but the quality of these logs is questionable and can only be assessed by looking at the full sonic waveform data.

Quality Control

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

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. 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 casing 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) and on the FMS tool (C1 and C2). The hole was in moderate condition for the TAP/DIT/HLDS/APS/HNGS/MGT tools string, ranging from in gauge (10 inches) at the bottom of the hole to very wide (> 18 inches) above 156 mbsf.

Additional information about the logs can be found in the “Explanatory Notes” and Site Chapter, ODP IR volume 208. For further questions about the logs, please contact:

Cristina Broglia

Phone: 845-365-8343

Fax: 845-365-3182

E-mail: Cristina Broglia