Wireline Standard Data Processing
ODP logging contractor: LDEO-BRG
Location: Hydrate Ridge - Cascadia Margin (NE Pacific)
Latitude: 44° 34.1166' N
Longitude: 125° 9.0025' W
Logging date: August 25-27, 2002
Water depth (as seen on logs): 806.5 mbrf
Total penetration: 180 mbsf
Total core recovered: 70.1 m (91 %)
Logging string 1: DIT/APS/HLDT/HNGS/QSST/TAP (main and repeat)
Logging string 2: FMS/GPIT/DSI/SGT (2 passes)
Logging string 3: VSI
Check shots with the in-line check shot tool (QSST) were acquired after the repeat run at the base of the hole. Zero-offset VSP stations were taken with the VSI at 5 m intervals between 83 and 173 mbsf. Walk-away VSP surveys along E-W and N-S lines were made with stations at 91, 138, and 172 mbsf.
The wireline heave compensator was used to counter ship heave.
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/HNGS/QSST/TAP: Bottom-hole assembly at 57 mbsf (main pass)
DIT/APS/HLDT/HNGS/QSST/TAP: Bottom-hole assembly at 60 mbsf (repeat pass)
FMS/GPIT/SGT/DSI: Bottom-hole assembly at 70 mbsf (both passes).
Depth shift: The DIT/APS/HLDT/HNGS/QSST/TAP repeat pass was depth matched to the DIT/APS/HLDT/HNGS/QSST/TAP main pass using the HSGR log. The caliper log from the FMS/GPIT/DSI/SGT pass 1 was depth matched to the caliper log from the DIT/APS/HLDT/HNGS/QSST/TAP main pass, and crosschecked with the gamma ray logs. The caliper logs from FMS/GPIT/DSI/SGT pass 2 was matched to the shifted caliper logs from pass 1. All logs were then shifted to the sea floor (-806.5 m). The sea floor depth was determined by the step in gamma ray values at the sediment-water interface. For Hole 1250F, it differs by 0.5m 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 and SGT 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.
Acoustic data processing: The dipole shear sonic imager (DSI) was operated in P&S monopole (pass 1 and 2), upper dipole (pass 1), and Stoneley and lower dipole modes (pass 2). Because of the slow formation, the automatic picking of delay times from sonic waveforms did not provide good results. Processing of the original waveforms was required to extract meaningful compressional and shear velocities. Only the velocities processed by Gilles Guerin are presented in the online database; they were obtained from the P&S monopole and dipole modes. The original waveforms are also available online.
High-resolution data: Bulk density and neutron porosity data were recorded at a sampling rate of 2.54 and 5.08 cm, respectively. SGT gamma ray data were sampled every 5.08 cm.
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. 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). The hole was in excellent condition, exceeding 12.5 inches diameter in only a few spots.
Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP IR volume 204. For further questions about the logs, please contact:
E-mail: Cristina Broglia