High Resolution Acoustic Televiewer
The HRAT provides a continuous high-resolution oriented ultrasound image of the borehole wall. The probe uses a fixed acoustic transducer and a rotating acoustic mirror to scan the borehole walls with a focussed ultrasound beam. The amplitude and travel time of the reflected acoustic signal are recorded as separate image logs.
Features such as fractures reduce the reflected amplitude and appear as dark sinusoidal traces on the log. The travel-time log is equivalent to a high-precision 360-arm caliper and shows diameter changes within open fractures and ‘break-outs’. Directional information is also recorded and used to orient the images in real time.
- Diameter: 42mm
- Length: 1.62m (2.06m with natural-gamma option)
- Transducer type: 1.5MHz piezo-composite
- Rotation rate: 5 – 20rev/s
- Sample rate: up to 360/rev
- Fracture identification and orientation
- Stratigraphic studies
- Local stress studies (break-out)
- Core orientation
- Cased-hole studies
Below: Acquisition of HRAT data with Micrologger2 Above middle: HRAT acoustic televiewer probe
Above right: travel time Far right: amplitude Below right: HRAT data used to orient core