The microresistivity curves recorded by dipmeters give much diverse information about evaporitic formations because these curves have a fine vertical resolution (approximately 1 cm) and show the very high contrast in resistivity between evaporites (with high resistivity) and clay and carbonate rocks, which are porous and conductive. Examples are taken from the Paleogene salt sequence and its overlying formations of the Bresse Trough in southeastern France.
The consistency of the 4 to 8 dipmeter curves allows clear recognition of different salt facies (primary salt, secondary salt, and mixed patches of clay and carbonate within displacive halite layers) and sulfate facies (massive anhydrite, nodular anhydrite, etc). The correlation of thin continuous carbonate and clastic beds using resistivity curves discloses, with a high degree of precision, the geometry of the various formations between wells. Examples show the detection of small-magnitude halite dissolution (a few meters vertically) and the lateral effect of anhydrite hydration.
In this paper, a method is proposed for determining structural dip of salt beds by computing dip angle and azimuth of thin conductive beds within the salt using the DUALDIP computer program. A frequency distribution plot of these dip angles and azimuths gives a good indication of the dip of the salt beds.