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HRAT - High Resolution Acoustic Televiewer

The HRAT is the latest RG development in acoustic borehole imaging and replaces the previous borehole televiewer probe (BHTV). It provides high-resolution orientated 'unwrapped' images of the borehole walls.

Applications 

  • Fracture identification and orientation
  • Stratigraphic studies
  • Local stress studies (break-out) Core orientation

Principles of Measurement 

The probe uses a fixed acoustic transducer and a rotating acoustic mirror to scan the borehole walls with a a focussed ultrasound beam. The amplitude and travel time of the reflected acoustic signal are recorded simultaneously as separate image logs. Features such as fractures reduce the relected amplitude and often 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. The HRAT includes many new features such as automatic optimisation of head rotation speed according to borehole diameter, cable speed and desired resolution. A new design of acoustic transducer provides improved image focus and resolution compared to the previous BHTV probe.

RG-DIP, the RG image interpretation package, offers manual and automatic feature recognition options. Feature orientations (dip/strike and azimuth) are automatically calculated. Display options include stereographic projections of zone axes, orintation frequency plots and 'synthetic cores' for comparison with real core data. The last option is invaluable for orientating core samples, particularly in the case of incompete recovery. The HRAT format is also compatible with the popular IMAGER interpretation package from Geomechanics International (GMI), available through RG.

Interpretation

Geolog now also offers interpretation of HiRAT (Borehole Televiewer) data. HiRAT data collection and interpretation can be arranged as a stand alone service or in combination with other wireline service and data presentation.