Publication Date:
2016-10-25
Description:
In the northern Barbados accretionary wedge, several Deep Sea Drilling
Project (DSDP) and Ocean Drilling Program (ODP) legs (DSDP Leg
78 and ODP Legs 110, 156, and 171A) targeted the décollement and the
seaward extension of the décollement, the proto-décollement. During
Leg 171A, the logging while drilling (LWD) technique was used to determine
the physical properties variations along a profile across the deformation
front. Because of the unstable borehole conditions in
accretionary wedges, LWD is the most effective method for the measurements
of physical properties in these poorly consolidated sediments.
LWD data are acquired just above the drill bit a few minutes
after the formation has been drilled, yielding measurements as close to
in situ conditions as possible.
The large amount of LWD data and the demand for a quick, objective,
and reliable evaluation calls for the application of multivariate statistical
methods. The multivariate factor analysis is a method of
reducing the amount of logging data while giving them a new integrated
meaning with no loss of important information, resulting in factor
logs that are helpful tools for further interpretation. The cluster
analysis of the two or three most significant factors proved to be a useful
and objective method to identify and confirm significant logging
units. The main objective of the application of multivariate statistical
methods in this study is twofold. First, Leg 171A was a stand-alone logging
leg, where no cores were retrieved. The factor analysis was used as
an objective tool for a classification of the drilled sequences based on
their physical and chemical properties. The new factor logs mirror the
basic processes behind the measured geophysical properties and make
them easier to interpret. Second, in the succeeding cluster analysis, similar
geophysical properties are grouped into one cluster, reflecting one
logging unit. These objectively defined logging units can be compared
to statistical electrofacies, which are helpful in differentiating lithologic
characterizations. In particular for LWD measurements, the multivariate
statistical methods of factor and cluster analysis are helpful tools for
a fast, reliable, and objective definition of logging units, which should
be considered for future legs.
Type:
Article
,
NonPeerReviewed
Format:
text
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