Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG

Hole: 1203A

Leg: 197

Location: Detroit Sea Mount (NW Pacific)

Latitude: 50° 56.9976' N

Longitude: 167° 44.3669' E

Logging date: 23-25 July, 2001

Bottom felt: 2604.4 mbrf

Total penetration: 914.6 mbsf

Total core recovered: 333.9 m (54.3 %)

Logging Runs

Logging string 1: DLL/HLDT/APS/HNGS (main and repeat pass)

Logging string 2: FMS/GPIT/NGT/DSI (2 passes - pass 1 in basement only)

Logging string 3: Gottingen magnetometer tool

No major problems were encountered while logging Hole 1203A; good logs were obtained, especially in the basement section. The hole was wider than 18 inches in the sediment section above 447 mbsf, reducing the quality of some logs. The third party Gottingen magnetometer tool was successfully deployed, taking a downlog and an uplog. Extra weight was added to ensure enough tension in the logging cable. The Gottingen susceptibility tool needed repairs and was not run.

Wireline heave compensator was used to counter ship heave resulting from the mild sea conditions.

Bottom-hole Assembly

The following bottom-hole assembly/pipe 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/HLDT/APS/HNGS: Bottom Hole Assembly at 202 mbsf.

FMS/GPIT/NGT/DSI: Bottom Hole Assembly at 202 mbsf.

The sediment/basement contact was at 465 mbsf.

Processing

Depth shift: The original logs were depth matched to the HSGR from the DLL/HLDT/APS/HNGS main pass and were then shifted to the sea floor (-2608 m). The sea floor depth could not be determined by the usual method of identifying the step in gamma ray values at the sediment-water interface. However, both the base of pipe and the basement contact were clearly identified, and both were about 4 m deeper than the equivalent driller's/core depths. Therefore the logs were shifted to ring them in line with the sediment-basement interface in the core and base of pipe. The logging sea-floor depth differs by 3.6m 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 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: NGT data have been processed to correct for borehole size and type of drilling fluid. The HNGS data were corrected for hole size during the recording.

Acoustic data: The DSI tool was operated in two modes for both passes: P&S and upper dipole mode. The results in the basement are generally good: only a handful of anomalous spikes were removed and replaced by a null value (see below). However, in the sediment section shallower than 352 mbsf, the wide hole caused problems, and data are unreliable. Compressional velocity has been calculated from the P&S mode slowness, shear velocity from the upper dipole mode.

Density data: The HLDT long spaced detector voltage became unstable during the main pass of the DLL/HLDT/APS/HNGS tool string, from 317-392 mbsf. The repeat pass was designed to cover this gap, and the Schlumberger engineer spliced the repeat density data into the main pass.

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.

Quality Control

Null value=-999.25. This value generally replaces recorded log values or results that are considered invalid (in this hole invalid acoustic data).

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) and on the FMS string (C1 and C2).

Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP Leg 197 IR volume. For further questions about the logs, please contact:

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