Schlumberger

Neutron Density Imaging Service

Overview Library

Azimuthal images of bulk density and caliper

The imaging density neutron standoff caliper tool provides a bulk density image, along with conventional bulk density, neutron porosity, and photoelectric index (PE) logs. Tool standoff and caliper measurements are provided by a pair of ultrasonic transducers.

Bulk density images are a graphical representation of the variation in bulk density around the circumference of the borehole. This imaging is possible because of the collimated source and detectors of the density tool that focus the density measurement on the formation directly in front of the sensor.

As the drillstring and tool rotate, the density and ultrasonic sensors are sampled at a high frequency, allowing compensated density, PE, and standoff data to be collected around the entire circumference of the borehole. A proprietary imaging algorithm employs a weighting technique to focus the measurements on discrete azimuths—or sectors—around the borehole. Memory images use 64 sectors, while images of up to 16 sectors can be transmitted to surface in real time.

Compensation for borehole quality

Readings from the ultrasonic transducers are used to make environmental corrections and to provide high-quality bulk density and neutron porosity measurements with the help of a proprietary standoff weighting technique. This algorithm gives the highest weight to a subset of the rotating data with minimum standoff from the borehole. Thus, data of the best possible quality is ensured even when hole conditions are poor. The highly rugged transducers are aligned with the density and neutron detectors for accurate dynamic standoff-based processing.

Geosteering applications and geomechanical analysis

The image functionality of the tool makes it ideal for geosteering applications. The contrast in the formation density and PE of adjacent beds results in the characteristic sinusoids on the image log that allow formation bed dips to be calculated and clearly indicate which direction the geological structure is being traversed. This information helps determine whether the drilling assembly should be steered up or down to remain in the zone of interest. Image data obtained from the ultrasonic transducers can be used to produce 3D views of the borehole for visualization of hole quality and wellbore stability and as an input for geomechanical analysis.

The tool can operate at temperatures up to 350 degF [175 degC] and pressures up to 25,000 psi.

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