Publication Date:
2016-10-10
Description:
All sites drilled on Leg 57 were logged as weather
conditions permitted. The logging was done by the Singapore
office of Schlumberger, and because of short
notice the special logging tools required to pass through
the Challenger drill pipe were not available. The standard
centralizer, excentralizer, and caliper tools were
not appropriate, and those modified aboard ship were
not completely satisfactory. In addition, we suspected
that vertical motion from the ship's heave degraded the
quality of logs. Both the sonic and neutron density tools
were operated beyond their normal working ranges. Despite
these operational difficulties, the logs from different
runs in a hole, both repeat sections and runs with
different tools, show generally the same features. Over
intervals of 5 to 10 meters the field logs seem to be good
indicators of the physical character of the section penetrated
(Carson and Bruns, this volume).
The recovery of continuous core as well as logs differs
from normal industrial drilling practice, in which a
major purpose of logging is to establish lithology. Since
lithology is best established by direct examination, the
log analysis focused less on identifying a specific lithology
than on continuous measurement of in situ
physical properties, especially at Sites 438, 439, and 440,
where recovery was good. However, the logs were used
to establish the lithology of missing intervals, especially
at Site 441, where recovery was poor. Lithology and
physical properties aspects of the log analysis are covered
in the individual site chapters and in a comparative
analysis of laboratory measurements of physical properties
and logged physical parameters (Carson and Bruns,
this volume). In the present chapter we concentrate on
log precision, correlation of key horizons in seismic
records and core lithology, and on fracturing as indicated
by the logs. We do this by using the results of a
study of corrected logs and the derivative products from
computer programs developed by the Scientific Software
Corporation (SSC) and Technology Research Center
and of corrected logs from Schlumberger (available
from DSDP).
Type:
Article
,
PeerReviewed
Format:
text
DOI:
10.2973/dsdp.proc.5657.150.1980
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