ODP logging contractor: LDEO-BRG
Hole: 1143A
Leg: 184
Location: Archipelago Islands (South China Sea)
Latitude: 9° 21.7194' N
Longitude: 113° 17.1018' E
Logging date: March, 1999
Bottom felt: 2782 mbrf
Total penetration: 400 mbsf
Total core recovered: 378.33 m (94.6 %)

Logging Runs

Logging string 1: DIT/APS/HLDS/HNGS
Logging string 2: FMS/GPIT/SDT/NGT
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/HLDS/HNGS: Bottom-hole assembly at 85 mbsf
FMS/GPIT/SDT/NGT: Bottom-hole assembly at 124.5 mbsf.

Processing

Depth shift: The original logs have been interactively depth-shifted with reference to HNGS from DIT/APS/HLDS/HNGS run and to the sea floor (-2781.5 m). This amount corresponds to the mudline depth as observed on the logs; it differs 0.5 m from the "bottom felt" depth given by the drillers (see above). The program used is an interactive, graphical depth-match program, which allows to visually correlate logs and to define appropriate shifts. The reference and match channels are displayed on the screen, with vectors connecting old (reference curve) and new (match curve) shift depths. The total gamma ray curve (SGR or HSGR) from the NGT or HNGS tool run on each logging string is used to correlate the logging runs most often. In general, the reference curve is chosen on the basis of constant, low cable tension and high cable speed (tools run at faster speeds are less likely to stick and are less susceptible to data degradation caused by ship heave). Other factors, however, such as the length of the logged interval, the presence of drill pipe, and the statistical quality of the collected data (better statistics is obtained at lower logging speeds) are also considered in the selection. The depth correlation between the reference and the match curve in this hole was difficult in the upper 220 m, where the log signature is quite different, possibly du to the dgraded hole conditions (swelling clays). A list of the amount of differential depth shifts applied at this hole is available upon request.

Gamma-ray processing: NGT data have been processed to correct for borehole size and type of drilling fluid. HNGS data have been corrected in real time during the recording.

Acoustic data processing: The SDT data, recorded in depth-derived, borehole compensated, long-spacing (8-10-10-12 ft) sonic mode are of excellent quality and do not need processing. Compressional velocity has been computed from DTLN adn DTLF.

High-resolution data: Neutron porosity data were recorded at a sampling rate of 5.08 cm.

Quality Control

null value=-999.25. This value may replace recorded 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, HLDS) 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, such as the gamma ray data above 85 and 124.5 mbsf, should be used qualitatively only because of the attenuation on the incoming signal.
Hole diameter was recorded by the caliper on the HLDS tool (LCAL) and FMS string (C1 and C2). All calipers show a worsening of the hole conditions in the upper 220m of the hole.

Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP IR volume 184. For further questions about the logs, please contact:

Trevor Williams
Phone: 845-365-8626
Fax: 845-365-3182
E-mail: Trevor Williams

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