LWD Standard Data Processing

 

ODP logging contractor: LDEO-BRG

Hole: 1249B

Leg: 204

Location: Hydrate Ridge Cascadia Margin (NE Pacific)

Latitude: 44° 34.211' N

Longitude: 125° 8.842' W

Logging date: July 24, 2002

Water Depth (as seen on logs): 788 mbrf

Total penetration: 74.9 mbsf

 

Logging Tools

 

The logs were recorded using the LWD (Logging-While-Drilling) technique, which allows acquisition of open-hole logs using instruments that are part of the drill string itself. The advantages of this technique include being able to log in formations that would not provide a stable hole for wireline logging (e.g. the upper section of sedimentary formations), and logging a hole immediately after it is drilled, so that it is in good condition and free of wash-outs.

 

The 'Logging While Coring' technology took place in Hole 1249B for the first time in the ODP. This consisted of a modified 8-inch RAB tool, which permits cores to be taken through it. The test was successful: RAB images were acquired and 8 cores were recovered (32.9% recovery).

 

In Hole 1249B the penetration rate generally ranged between 10 and 25 m/hr.

 

 

Processing

 

Depth shift: Original logs have been depth shifted to the sea floor (-788 m). The sea floor depth was determined by the step in gamma ray and resistivity values at the sediment-water interface.

 

Gamma Ray data: Processing of the data is performed in real-time onboard by Schlumberger personnel. Gamma Ray data is measured as Natural Gamma Ray (GR): it has been corrected for hole size (bit size), collar size, and type of drilling fluid.

 

Resistivity data: The resistivity curves are sampled at a 0.0304 m (1.2 in) sampling rate.

 

Quality Control

 

During the processing, quality control of the data is mainly performed by cross-correlation of all logging data. The best data are acquired in a circular borehole.

 

Additional information about the logs can be found in the 'Explanatory Notes' and Site Chapter, ODP IR volume 204. For further questions about the logs, please contact:

 

Cristina Broglia

Phone: 845-365-8343

Fax: 845-365-3182

E-mail: Cristina Broglia