Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG

Hole: 1256D

Leg: 206

Location: Guatemala Basin (NE equatorial Pacific)

Latitude: 6° 44.163' N

Longitude: 91° 56.061' W

Logging date: December 28-30, 2002

Bottom felt: 3645.4 mbrf

Total penetration: 752 mbsf

Total core recovered: 227.3 (47.8%)

Logging Runs

Logging string 1:DLL/HLDT/APS/HNGS/TAP (main and repeat passes: TAP failed)

Logging string 2: FMS/GPIT/DSI/SGT (one pass, FMS failed)

Logging string 3: FMS/GPIT/SGT (3 passes)

Logging string 4: German magnetometer tool (failed)

Logging string 5: UBI/GPIT/SGT (main and repeat passes)

Logging string 6: WST (12 check-shot stations)

Logging string 7: German magnetometer tool (failed)

All of the main passes reached close to the total depth without problems from bridges. The wireline heave compensator stopped at 529 mbsf during the main DLL/APS/HLDT/HNGS/TAP pass, but was started again for subsequent logging.

Casing

The 16" casing was set at 269 mbsf.

Processing

Depth shift: The original logs were depth matched to the ECGR and caliper logs from the first pass of the FMS/GPIT/SGT tool string; then they were shifted to the sea floor (-3643.5 m). The sea floor depth was not determined directly; the sea floor depth was set so that the bottom of the casing in the logs appeared at the same depth (269 m) as given by the drillers. For Hole 1256D, it differs by 1.9 m from the "bottom felt" depth given by the drillers (see above).

Depth matching is typically done in the following way. One log is chosen as reference (base) log (usually the total gamma ray log from the run with the greatest vertical extent), and then the features in the equivalent logs from the other runs are matched to it in turn. This matching is performed manually. The depth adjustments that were required to bring the match log in line with the base log are then applied to all the other logs from the same tool string.

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

Acoustic data processing: The dipole shear sonic imager (DSI) was operated in P&S monopole and lower dipole modes.

High-resolution data: Bulk density and neutron porosity data were recorded at a sampling rate of 2.54 and 5.08 cm, respectively. SGT gamma ray was recorded at 15.24 and 5.08 cm sampling rates.

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, 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 casing 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 tool (C1 and C2). The hole was in very good condition, generally reading between 10-12 inches in diameter. Slightly wider sections with thin washouts occur at 348-403, 418-435, 450-473, 530-605, and 678-694 mbsf.

Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP IR volume 206. For further questions about the logs, please contact:

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