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
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.
Processing
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