Insights from simultaneous acoustic and resistivity imaging

Abstract

We describe a method of thin-bed petrophysical analysis that exploits the availability of both acoustic and resistivity images of the same rock. In developing our method we have gained a number of insights into the contrasting response of these images to rock properties, which may be of general interest to the imaging community. The case-study we present is from a thin-bedded, deep-water siliciclastic depositional environment. The resistivity image was used to increase the resolution of a conventional resistivity device. Comparison of bedding dips between the two images suggests a resistivity depth of investigation of around three inches. However, the best fit between image and conventional resistivity was obtained using a somewhat deep-reading resistivity measurement. The acoustic image was used to increase the resolution of our porosity measurement. The best fit to acoustic image amplitude was with the neutron porosity log, rather than with density, slowness, or with any combination of two porosity logs. Given high-resolution resistivity and porosity measurements from the images, and the precise information on bed boundaries that images provide, we proceeded with petrophysical analysis at a much higher resolution than obtainable from the conventional logging suite.

Microresistivity and ultrasonic imagers: tool operations and processing principles with reference to commonly encountered image artefacts

“…It is noted that the two types of images are complimentary. Hayman et al (1994) and Hansen & Parkinson (1999) show how interpretation can indeed be enhanced when both types of images are available.…”

“…It would be safer in such cases to compare dips from microresistivity devices with cores or other measurements. Hansen & Parkinson (1999) report a depth of investigation of 5-7 cm in a study comparing images from microresistivity and ultrasonic devices. Trouiller et al (1989) mention that in thick homogeneous or finely laminated beds, the depth of investigation of a button is similar to that of a shallow laterolog, which is roughly 25 cm.…”

High-resolution petrophysical characterization of samples from an aeolian sandstone: the Permian Penrith sandstone of NW England

“…The difficulty is in obtaining a quantitative resistivity measurement at a similar scale to the resolution of the imaging device. In thickly bedded, homogeneous sequences the constraints are such that calibration may be feasible (Hansen & Parkinson 1999). Unfortunately, in thinly bedded or heterogeneous zones the devices sample different volumes and thus comparison and calibration is less reliable.…”