Print this pageResistivity Calibration Technique for Micro-Resistivity Image Logs: Applications for Thin-Bedded, Shaly Sand Reservoirs, Gulf of Mexico
GLOBE, MICHAEL J., WAYNE K. CAMP and ROGER D. HAIRR
A new technique is presented for calibrating resistivity measurements recorded by micro-resistivity image devices. This technique involves converting the recorded electrical power measurements to a scaled true resistivity. The scaled micro-resistivity curve represents an average of multiple sensors on a given pad or pad and flap combination. This scaled average curve agrees well with standard electric log shallow resistivity measurements over equivalent intervals. The scaled image log allows for accurate and quantitative resistivity comparisons that is not possible with the standard processed image logs.
Pseudo-color borehole images were generated from the scaled micro-resistivity curves and compared with core data from two offshore Gulf of Mexico fields to evaluate their reliability. Dynamic normalization image enhancement techniques resulted in greater resolution of apparent stratigraphic details in the uncalibrated images. Dynamic normalized uncalibrated images may reflect real resistivity variations in the well bore, resolving subtle textural variations in grain size and clay morphology, and thus may be preferred for certain log interpretation applications. The calibrated images exhibited better correlation to lithologic features observed from the cores. The scaled images allow for quantitative resistivity variations which may be useful in characterizing hydrocarbon saturations within the flushed zone of the wellbore. The scaled images are preferred for net pay and net sand counts within thin-bedded shaly sand reservoirs.