Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG

Hole: 1230A

Leg: 201

Location: Peru Margin (equatorial SE Pacific)

Latitude: 9° 6.753'S

Longitude: 80°35.010'W

Logging date: March16, 2002

Bottom felt: 5097 mbrf

Total penetration: 278.3 mbsf

Total core recovered: 187.3 m (67.6%)

Logging Runs

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

Logging string 2: FMS/GPIT/NGT/DSI (2 passes)

No problems were encountered while logging Hole 1230A. Logs are of good quality. 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/APS/HLDT/SGT/HNGS: Bottom Hole Assembly at ~80 mbsf (main pass)

FMS/DSI/GPIT/NGT: Bottom Hole Assembly at ~80 mbsf (pass 1)

FMS/DSI/GPIT/NGT: Bottom Hole Assembly at ~71 mbsf (pass 2).

Processing

Depth shift: The original logs were depth matched to the HSGR from the DIT/APS/HLDT/SGT/HNGS main pass and were then shifted to the sea floor (-5099 m). The sea floor depth is determined by the step in gamma ray values at the sediment-water interface. For Hole 1229A, it differs by 2 m from the "bottom felt" depth given by the drillers (see above).

Depth matching is 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: HNGS and SGT data were corrected for hole size during the recording

Acoustic data: The DSI tool was operated in the following modes: P&S monopole, upper dipole (high frequency), and Stoneley modes for Pass 1; P&S monopole, upper dipole (low frequency), lower dipole (high frequency), and FMD (first motion detection) modes for Pass 2. The compressional wave velocity data from the P&S mode are generally of acceptable quality, with good repeatability between pass 1 and 2. Shear wave velocity data are locally good, however some data is invalid because the shear wave peaks in the slowness time-coherence plot were often difficult to pick, particularly in the slower formations. Shear data from the upper dipole are presented in the data files. The Stoneley wave data is invalid above 187 mbsf. Post-cruise work would likely improve the velocity logs.

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. 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 recorded data or results.

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. 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 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 borehole was moderately variable in diameter, ranging from 13" to 18" in (the maximum extent of the caliper arm). There is a wide (>18") section between 185 and 210 mbsf; between 111 and 161 mbsf the hole is 13-14.5" wide; the hole diameter is highly variable between 211 and 247 mbsf.

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