Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG

Hole: 1073A

Leg: 174A

Location: New Jersey Rise (NW Atlantic)

Latitude: 39° 13.5214' N

Longitude: 72° 16.5461' W

Logging date: July, 1997

Bottom felt: 650.9 mbrf

Total penetration: 663.6 mbsf

Total core recovered: 663 m (99.9 %)

Logging Runs

Logging string 1: DIT/SDT/NGT (upper, middle, and lower sections)

Logging string 2: DIT/APS/HLDS/HNGS (lower section)

Wireline heave compensator was used to counter ship heave.

Bottom-hole Assembly/Pipe

The following bottom-hole assembly and 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.

DIT/SDT/NGT: Bottom-hole assembly at ~85 mbsf (upper section)

DIT/SDT/NGT: Drill pipe at ~25 mbsf (upper section)

DIT/SDT/NGT: Bottom-hole assembly at ~358 (middle section)

DIT/SDT/NGT: Bottom-hole assembly at ~343 mbsf (lower section)

DIT/SDT/NGT: Drill pipe at ~283 mbsf (lower section)

DIT/APS/HLDS/HNGS: Bottom-hole assembly at ~358 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 (- 650 m). In particular, the lower section of the DIT/SDT/NGT has been shifted with reference to the upper section while the middle section of the DIT/SDT/NGT and the lower section of the DIT/APS/HLDS/HNGS have been matched to the shifted NGT from the lower section. 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. A list of the amount of differential depth shifts applied at this hole is available upon request.

Gamma-ray processing: NGT and HNGS data have been processed to correct for borehole size and type of drilling fluid.

Acoustic data processing: The SDT sonic data recorded in three sections are of excellent quality; they have been have been processed to eliminate some of the minor cycle skips 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. The data from the three sections has been merged as follows:

upper section: 87.5-250 mbsf

middle section: 250-350 mbsf

lower section: 350-639 mbsf.

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 log values or results which 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, HLDS) and a good contact with the borehole wall. The data is generally of very good quality, with the exception of the APS/HLDS data over those intervals where the hole is very enlarged (for example in the 419-443 and 457-465 mbsf intervals).

Data recorded through bottom-hole assembly should be used qualitatively only because of the attenuation on the incoming signal. Invalid gamma ray data were recorded at 78-81 mbsf.

Hole diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL).

Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP IR volume 174A. For further questions about the logs, please contact:

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