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.