Construction
of Cross Sections and Maps from Dipmeter Data
Arnaud Etchecopar
This work describes a new use of dipmeter data for constructing geological cross sections and maps near boreholes. This method, called the similar fold method, is now implemented in the Schlumberger Geological Advisor.
The method relies on two hypotheses. First, layers are assumed to be
initially parallel, which implies the method cannot be applied if a major
unconformity exists in the selected interval. Second, each structure of
deformation is regarded as a similar fold, so that each stratification can be
constructed from the others by a translation parallel to the axial plain for a
fold or parallel to the fault
plane
for brittle structures. This model is
appropriate for drags and rollovers and is a good approximation of folded
structures.
An interactive computer procedure has been developed which comprises three
steps. (1) Localize major discontinuities (i.e., faults, unconformities) and
compute the fault
plane
or the axial
plane
of the continuous structures (i.e.,
folds, drags, rollovers) between them. Axial
plane
or
fault
determination has
been automated, even in the case of overturned points. (2) Generate the cross
section by translating the different dip traces parallel to the axial
plane
or
to the
fault
plane
determined above. (3) Construct the map from cross sections
at different azimuths.
Different examples analyzed with this method show realistic results, although somewhat crude due to the initial approximation of structures by similar folds (parallel translation). Work is under way to use such cross sections and maps to improve borehole seismic migration near the wells.
AAPG Search and Discovery Article #91032©1988 Mediterranean Basins Conference and Exhibition, Nice, France, 25-28 September 1988.