A Single Shot instrument is capable of one survey per trip into the borehole. In all applications where a directional or tool-facing survey is carried out periodically as the hole is drilled, a single shot instrument is the choice. This procedure will identify the course and position of the hole and whether the deviation is acceptable as the bore is
drilled. Tool-facing surveys could consist of core orientation, wedge setting or in-hole motor directional drilling- all of which are the realm of the single shot instrument.
Multishot instruments can produce a number of surveys per trip and in most cases some control on the frequency of surveys is available. We do not recommend multishot magnetic azimuth instruments in freshly drilled holes in hard rock (see "Azimuth and Relative Heading Surveys"), but many of the relative direction Multishots are particularly efficient when dog-legs (abrupt changes in hole direction) have to be identified or when there is no need to hit a target but the position of the hole must be known. In the latter case, the hole is drilled and sampled and the surveyed. Multishots are also efficient where a large number of previously drilled holes have to be surveyed- the case in all blast-hole arrays. |
