Par VAN PHON NGUYEN et A. BABSKOW
It is well known that the resistivity values indicated by the usual electrical
logging arrangements (normal, lateral), are only apparent resistivities which
must be corrected for obtaining actual rock resistivity values for the influence
of the mud in the well bore and in the invaded zone.
In the classical method of calculation, using charts for the lateral electrical
sounding, the invaded zone is admitted to have a constant resistivity throughout
its extension. This hypothesis is certainly not conformal to reality, because
the mud cannot be uniformly spread in the invaded zone. The media theory allows
to study a model which is probably more adequate to represent the reality.
In this model the resistivity varies continuously from its value on the wall
of the hole to its value in the uncontaminated zone. Analytical formulae are
established for the apparent resistivity. Organigrams and a set of lateral
sounding curves, calculated for particular values of the parameters involved,
are presented.