Wireline Standard Data Processing
ODP logging
contractor: LDEO-BRG
Well name: 770C
Leg: 124
Location: Celebes Basin (Celebes Sea)
Latitude: 5° 8.69' N
Longitude: 123° 40.11' E
Logging date: December, 1988
Bottom felt: 4516.2 mbrf (used for depth shift to sea floor)
Total penetration: 529.5 mbsf
Total core recovered: 54.8 m (47.3 %)
Logging
Runs
Logging string 1: DIT/SDT/NGT
Logging string 2: ACT/GST/GPIT/NGT
Logging string 3: LDT/CNTG/NGT
No information available could be found about use of wireline heave compensator to counter ship heave.
Bottom-hole
Assembly/Pipe/Casing
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 and drill string and/or wireline stretch.
DIT/SDT/NGT: Bottom-hole assembly at ~124 mbsf
ACT/GST/GPIT/NGT: Bottom-hole assembly at ~124 mbsf
LDT/CNTG//NGT: Bottom-hole assembly at ~124 mbsf.
Processing
Depth shift: Original logs have been interactively depth shifted with reference to NGT from DIT/SDT/NGT run and to the sea floor (- 4516.2 m). 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) from the NGT 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. A list of the amount of differential depth shifts applied at this hole is available upon request.
Gamma-ray processing: NGT data from the DIT/SDT/NGT and ACT/GST/GPIT/NGT runs have been processed to correct for borehole size and type of drilling fluid. The LDT/CNT/NGT tool string was deployed after the ACT/GST/GPIT/NGT and the formation had been radioactively activated. For this reason, no processing has been performed on the NGT from the LDT/CNT/NGT tool string. The original data have therefore been included in the database. Also, all logging runs were recorded using the Sidewall Entry Sub, a device that allows the wireline to be run outside the drill pipe, thus allowing to record data as pipe is simultaneously pulled back and hole is exposed. This resulted occasionally in spurious spikes when part of the tool string entered momentarily the drill pipe. Such spikes were observed at 350 mbsf (DIT/SDT/NGT) and 141-148, and 312-322 mbsf (ACT/GST/GPIT/NGT). Other invalid spikes occurring when the tool string was momentarily stationary in the hole were observed at 452, and 461 mbsf (ACT/GST/GPIT/NGT).
Acoustic data processing: The SDT logs have been processed to eliminate some of the noise and cycle skipping experienced during the recording. Using two sets of the four transit time measurements and proper depth justification, four independent measurements over a -2ft interval centered on the depth of interest are determined, each based on the difference between a pair of transmitters and receivers. The program discards any transit time that is negative or falls outside a range of meaningful values selected by the processor.
Geochemical data: Due to technical problems, no geochemical data from this hole could be migrated into the online database. The results of the processing, however, can be viewed in the paper by Pratson, E. et al. (1991), Data Report: geochemical; results from wireline logs in the Celebes Sea, Sites 767 and 770 of Leg 124. In Silver, E. A., Rangin, C., von Breymann, M. T. et al., Proc. ODP, Sci. Results, 124: College Station, TX (Ocean Drilling Program): 541-552.
Quality
Control
null value=-999.25. This value may replace invalid recorded log values or results (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 (CNTG, LDT) and a good contact with the borehole wall. he first two runs (lower repeat and main run) of the LDT/CNT/NGT tool string yielded incorrect near-detector count rates due to improper calibration of the short-spacing detector. The long-spacing readings are used instead, but they are not corrected for hole diameter, as no caliper measurement was performed. Data recorded through bottom-hole assembly should be used qualitatively only because of the attenuation on the incoming signal.
Invalid resistivity spikes were recorded at 142.5, 158, 266, 306, and 341 mbsf. No valid measurement of hole diameter was recorded at this hole.
Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP IR volume 124. For further questions about the logs, please contact:
Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia