LWD Standard Data Processing
ODP logging
contractor: LDEO-BRG
Hole: 1249B
Leg: 204
Location: Hydrate Ridge Ü 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
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