Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG

Hole: 1225A

Leg: 201

Location: East Pacific Rise (equatorial NE Pacific)

Latitude: 2°46.247' N

Longitude: 110°34.289' W

Logging date: February 11, 2002

Bottom felt: 3772 mbrf

Total penetration: 319.6 mbsf

Total core recovered: 321.6 m (101.9%)

Logging Runs

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

Good quality logs were obtained at Hole 1125A. The SGT (Scintillation Gamma Tool) was run for the first time in ODP. 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.

DIT/HLDT/APS/HNGS/SGT: Bottom Hole Assembly at 79 mbsf (main pass).

Processing

Depth shift: The original logs were depth matched to the HSGR from the main DIT/HLDT/APS/HNGS pass and were then shifted to the sea floor (-3772.3 m). It differs by 0.3 m from the "bottom felt" depth given by the drillers (see above). The sea floor depth is determined by the step in gamma ray values at the sediment-water interface.

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. In this case, the SFLU resistivity was used to match the repeat to the main pass, because it had more correlatable features than the gamma logs (gamma radiation levels were quite low).

Gamma-ray processing: The HNGS data were corrected for hole size during the recording. The SGT data were not corrected for hole size.

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 SGT gamma ray was recorded at 15.24 and 5.08 cm sampling rates.

Quality Control

Null value=-999.25. This value may replace recorded log values or results that are considered invalid.

During the processing, quality control of the data is mainly performed by inter-comparison 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). Hole width varies from 13 inches to beyond 18 inches (the maximum extent of the caliper arm).

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

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