Standard Wireline Data Processing

 

DSDP operator and logging contractor: Scripps Institution of Oceanography

Hole: 499D

Leg: 67

Location: Mid America Trench (tropical NE Pacific)

Latitude: 12¡ 40.45' N

Longitude: 90° 56.7' W

Logging date: June 1979

Sea floor depth ("bottom felt"): 6126 mbrf

Total penetration: 216 mbsf

Total core recovered: 0.75 m (0.21 % of cored section)

Oldest sediment cored: not available

Lithologies: Turbidites, calcareous ooze and chalk, and basalt rubble

Data

 

The logging data was recorded by Gearhart-Owen in GO format. The data was digitized by Centerline Data and subsequently processed at the Borehole Research Group of the Lamont-Doherty Earth Observatory in February 2005.

 

Logging Runs

 

Tool string Pass Top depth (mbsf) Bottom depth (mbsf) Bit depth (mbsf) Notes
1. TEMP
Downlog
65
202
Reference
2. BHC/CL/GR
Main
124.1
195.8
Repeat
123.7
200.3

 

 

There is no reference to logging operations in Hole 499D in the DSDP Site Report; information was gathered from the log headers. The temperature log was run first, six hours after circulation stopped.

 

The depths in the table are for the processed logs (after depth matching between passes and depth shift to the sea floor). Generally, discrepancies may exist between the sea floor depths determined from the downhole logs and those determined by the drillers from the pipe length. Typical reasons for depth discrepancies are ship heave, wireline and pipe stretch, tides, and the difficulty of getting an accurate sea floor from the "bottom felt" depth in soft sediment.

 

Processing

 

Depth match and depth shift to sea floor: The repeat run of the BHC/CL/GR logs were depth matched to the main run; all logs were then shifted to the sea floor (-6126 m).

 

Depth matching is typically 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 no sudden changes in cable speed), and then the features in the equivalent logs from the other runs are matched to it in turn. This matching is performed manually. 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.

 

Because no log crossed the mudline, the sea floor depth used to depth shift the data was the "bottom felt" depth (-6126 mbrf) given by the drillers.

 

Quality Control

 

The quality of the data is assessed by checking against reasonable values for the logged lithologies, by repeatability between different passes of the same tool, and by correspondence between logs affected by the same formation property (e.g. the resistivity log should show similar features to the sonic velocity log). The acoustic, gamma ray, and caliper logs show some similar features in the main and repeat pass, though the acoustic log is generally of poor quality.

 

Hole diameter was recorded by the 3-arm mechanical caliper (CL) on the acoustic tool string.

 

A null value of -999.25 may replace invalid log values.

 

Additional information about Hole 499D can be found in the Site Chapter in DSDP Initial Reports volume 67. For further questions about the logs, please contact:

 

Cristina Broglia

Phone: 845-365-8343

Fax: 845-365-3182

E-mail: Cristina Broglia