Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG

Hole: 1256C

Leg: 206

Location: Guatemala Basin (NE equatorial Pacific)

Latitude: 6° 44.179' N

Longitude: 91° 56.059' W

Logging date: November 21-22, 2002

Bottom felt: 3645.4 mbrf

Total penetration: 340.3 mbsf

Total core recovered: n/a

Logging Runs

Logging string 1: DLL/APS/HLDT/HNGS/TAP (two upper passes, one lower pass)

There was a bridge in the hole; two upper passes were made from the bridge up. The pipe was then lowered beneath the bridge, and a lower pass was made. The lower pass successfully logged the sediment-basement contact. Another bridge prevented any recording with the FMS/DSI/GPIT/SGT tool string.

The wireline heave compensator was used to counter ship heave.

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.

DLL/APS/HLDT/HNGS/TAP: bottom hole assembly at 108 mbsf (upper pass)

DLL/APS/HLDT/HNGS/TAP: bottom hole assembly at 217 mbsf (lower pass)

Processing

Depth shift: The two upper DLL/APS/HLDT/HNGS/TAP passes were on depth with each other and no depth matching was required. There was no data overlap with the lower pass. All logs were then shifted to the sea floor (-3640 m). The sea floor depth was difficult to determine exclusively from the logs - there was no clear step in gamma radiation at the sea floor. The sea floor depth was chosen so that the sediment basement contact was at 251.7 mbsf, like the core data. This shift is supported by the fact that the step in RHOB is shifted so that it occurs near the sea floor. For Hole 1256C, it differs by 5.4 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 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.

High-resolution data: Bulk density and neutron porosity data were recorded at a sampling rate of 2.54 and 5.08 cm, respectively.

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.

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 hole was in excellent condition in the basalt section, below 252 mbsf, mostly reading 12 inches except for a bridge at 257 mbsf. The sediment section is wider exceeding 18 inches in diameter for most of the interval.

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