Logging-While-Drilling Data Processing


ODP logging contractor: LDEO-BRG

Well name: 1275C

Leg: 209

Location: Mid-Atlantic Ridge (tropical NW Atlantic)

Latitude: 15° 44.4408' N

Longitude: 46° 54.2234' W

Logging date: June 25, 2003

Water Depth (ass seen on logs): 1565 mbrf

Total penetration: 20 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 RAB tool used on Leg 209 was the RAB-8 (RAB-while-coring) system, used with a standard 9.875 in. ODP RCB bit.


In Hole 1275C the penetration rate generally ranged between 1 and 3 m/hr.




Depth shift: Original logs have been depth shifted to the sea floor (-1565 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: 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 209. For further questions about the logs, please contact:


Cristina Broglia

Phone: 845-365-8343

Fax: 845-365-3182

E-mail: Cristina Broglia