Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG

Well name: 652A

Leg: 107

Location: Sardinia Margin (Tyrrhenian Sea)

Latitude: 40° 21.30' N

Longitude: 12° 8.59' E

Logging date: January, 1986

Bottom felt: 3470.5 mbrf (used for depth shift to sea floor)

Total penetration: 721.1 mbsf

Total core recovered: 445.7 m (61.2 %)

Logging Runs

Logging string 1: DIT/LSS/GR (upper and lower sections)

Logging string 2: GST/CNTG/NGT (upper and lower sections)

Neither tool string could reach the bottom of the hole due to an impassable bridge at about 371 mbsf.

The wireline heave compensator broke down and could not be used; ship heave ranged between 1 and 4 ft.

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 and drill string and/or wireline stretch.

DIT/LSS/GR: Bottom-hole assembly at ~ 74 mbsf (upper section)

DIT/LSS/GR: Bottom-hole assembly at ~ 108 mbsf (lower section)

GST/CNTG/NGT: Bottom-hole assembly at ~ 73 mbsf (upper section)

GST/CNTG/NGT: Bottom-hole assembly at ~ 258 mbsf (lower section).

Processing

Depth shift: Original logs have been interactively depth shifted with reference to NGT from DIT/LSS/GR and to the sea floor (- 3470.5 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 GR curve on the DIT/LSS/GR tool string and the total gamma ray curves (SGR) from the NGT tool run on the GST/CNTG/NGT tool string are used to correlate the logging runs at Hole 652A. 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 have been processed to correct for borehole size and type of drilling fluid.

Acoustic data processing: Acoustic data were acquired by the Long Spacing Sonic tool. The sonic 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: The elemental yields recorded by the GST tool represent the relative contribution of only some of the rock-forming elements (iron, calcium, chlorine, silicon, sulfur, hydrogen, gadolinium, and titanium - the last two ones computed during geochemical processing) to the total spectrum. Because other rock-forming elements are present in the formation (such as aluminum, potassium, etc.), caution is recommended in using the yields to infer lithologic changes. Instead, ratios are more appropriate to determine changes in the macroscopic properties of the formation. The ACT (Aluminum Clay Tool) was introduced during Leg 109, when it became routinely part of the geochemical tool string. For this reason, until Leg 109 no geochemical processing was performed and therefore the elemental yields should be used cautiously to infer lithologic changes.

Quality Control

null value=-999.25. This value generally appears in discrete core measurement files and also it 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 (CNTG) and a good contact with the borehole wall.

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 3-arm mechanical caliper device (MCD) on the DIT/LSS/GR tool string.

Additional information about the logs can be found in the "Explanatory Notes" and relevant Site Chapter, ODP IR volume 107. For further questions about the logs, please contact:

Cristina Broglia

Phone: 845-365-8343

Fax: 845-365-3182

E-mail: Cristina Broglia