The data provides information about geology, structure, fractures, stress orientation and acts as a template for orientating cores and providing depth control where core recovery is incomplete.
The High Resolution Optical Televiewer (Hi-OPTV) provides a continuous very high resolution oriented image of the borehole walls using a conventional light source. A unique optical system based on a fisheye lens allows the probe to survey 360 degrees simultaneously. This information is processed in real time to produce a complete ‘unwrapped’ image of the borehole oriented to magnetic north. The probe offers superior resolution to the High Resolution Acoustic Televiewer (HRAT) and produces images in real colour. While, unlike the HRAT, it can operate in air-filled boreholes, it is unsuitable for boreholes containing mud or cloudy fluids.
The High Resolution Acoustic Televiewer (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 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.