Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG

Hole: 1226B

Leg: 201

Location: East Pacific Rise (equatorial NE Pacific)

Latitude: 3° 5.6686' S

Longitude: 90°49.0793' W

Logging date: February 23, 2002

Bottom felt: 3308 mbrf

Total penetration: 421.4mbsf

Total core recovered: 413.7 m (98.8 %)

Logging Runs

Logging string 1: DIT/HLDT/APS/HNGS/SGT/TAP (main and repeat)

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.

DIT/HLDT/APS/HNGS/SGT/TAP: Bottom-hole assembly at ~ 66 mbsf (main)

DIT/HLDT/APS/HNGS/SGT/TAP: Recorded open-hole (repeat).

Processing

Depth shift: The original logs were depth matched to the HNGS from the DIT/HLDT/APS/HNGS/SGT/TAP main run and were then shifted to the sea floor (-3309.5m). The sea floor depth is determined by the step in gamma ray values at the sediment-water interface. This sea-floor depth differs by 1.5 m from the drillers (mud line) sea-floor depth (3308 mbrf).

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 automatically, and the result checked and adjusted as necessary. 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.

Gamma-ray processing: The HNGS and SGT data were corrected for hole size 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 HLDT pad and the borehole wall (low-density correction) the results are improved, because the short spacing has better vertical resolution.

The natural gamma ray log from the SGT tool was sampled every 5.08 cm, in addition to the normal sampling frequency.

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 good condition with a diameter of 13-14" from 263 to 410 mbsf. From 200 to 255 mbsf there is a very wide section (>18"), with a variable diameter above 200 mbsf.

Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP IR volume 201. For further questions about the logs, please contact:

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