Wireline Standard Data Processing
ODP logging contractor: LDEO-BRG
Location: Philippine Abyssal Plain (Philippine Sea)
Latitude: 19° 17.8165' N
Longitude: 135° 5.9519' E
Logging date: April 12, 2001
Bottom felt: 5720 mbrf
Total penetration: 800 mbsf
Total core recovered: 406.8 m (67.8 %)
Logging string 1: DLL/APS/HLDT/HNGS (downlog, upper, lower, and repeat)
Logging string 2: FMS/GPIT/SDT/NGT (2 passes)
During the DLL/APS/HLDT/HNGS main pass, the tool became stuck for a short time near 420 mbsf and the acquisition system was re-booted: hence the main pass is divided into upper and lower sections. New acquisition software, used for the first time in ODP at this site, created some complications to the logs and log processing (see below).
Wireline heave compensator was used to counter minor ship heave due to the calm seas.
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.
DLL/APS/HLDT/HNGS: Bottom-hole assembly at ~ 80 mbsf
FMS/GPIT/SDT/NGT: Bottom-hole assembly at ~ 116 mbsf (Pass 1)
FMS/GPIT/SDT/NGT: Bottom-hole assembly at ~ 79.5 mbsf (Pass 2).
Depth shift: Usually, depth matching between runs 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.
In Hole 1201D depth matching was more complex, because during log acquisition, the uplogs were created with a new operating software that uses a real-time speed correction as a default. This speed correction, however, appears to have introduced some depth discrepancies; the speed correction was removed after logging, resulting in a second set of log curves, which have their own peculiarities. Only the DLL/APS/HLDT/HNGS downlog was initially taken without the speed correction, so we have used the resistivity (LLD) log from that run as the depth reference.
After viewing both sets of logs, it was decided that the speed-corrected logs from the DLL/APS/HLDT/HNGS runs (uplogs) were superior to the logs with the speed correction removed, and that depth-matching to the DLL/APS/HLDT/HNGS downlog would correct for the depth discrepancies. The HNGS downlog was not ideal for matching, because the logging speed was quite fast, and all the NGT logs from the FMS/GPIT/SDT/NGT run were bad, so a combination of matches was used, based on the LLD downlog:
DLL logs LLD (lower, upper, and repeat) to LLD (downlog)
HLDT and APS logs RHOB (lower and upper) to LLD (downlog)
RHOB (repeat) to RHOB (matched upper section)
HNGS logs HSGR (lower and upper) to HSGR (downlog)
HSGR (repeat) to HSGR (matched upper section)
SDT logs DTLF (pass 1) to LLD (matched upper section)
DTLF (pass 2) to DTLF (matched pass 1)
The SDT logs with the speed correction removed were of better quality, so they were preferred to the speed corrected logs.
The matched logs were then shifted to the sea floor (-5725 m). The sea floor depth was determined by the step in the RHOB log, in the absence of any step in the gamma ray values at the sediment-water interface. The sea-floor value is 5 m different from the "bottom felt" depth given by the drillers (see above).
The best data from the overlapping DLL/APS/HLDT/HNGS runs were spliced to make composite logs:
DLL: 92.5-130 mbsf (repeat), 130-405 mbsf (upper), 405-430 mbsf (downlog), 430-581.5 mbsf (lower)
HLDT/APS: 79-408 mbsf (upper), 408-585 mbsf (lower)
HNGS: 0-378 mbsf (upper), 378-400 mbsf (downlog), 400-567 mbsf (lower)
Gamma-ray processing: NGT data were not processed because they were of very poor quality.
Acoustic data processing: The SDT was operated in DDBHC long-spacingmode. The data is of excellent quality and did not need any editing. The DTLN and DTLF slownesses have been converted into velocities.
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.
null value=-999.25. This value generally replaces recorded log values or results that are considered invalid (ex. processed sonic data).
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 is generally in good condition, with the diameter between 10 and 14 inches for most of the logged interval. The hole narrows around 420 mbsf, and is wider than 17 inches between 460-500 mbsf.
There is bad HLDT data between 447-453 mbsf, and bad DLL data between 408-428 mbsf.
Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP IR volume 195. For further questions about the logs, please contact:
E-mail: Cristina Broglia