< Return to Guidelines

Guidance

The sonde method as outlined in the general method description is the most common and most easily implemented of tracking methods that allow the operator to keep the borehole on its intended path. As the borehole depth increases, however, sonde methods eventually become ineffective (depending on the soil characteristics). For deeper bores, the most common tracking method uses a “wireline” to connect a tracking mechanism behind the drill head to the surface. This wireline connection presents difficulties because the connection must be maintained as new sections of drill rod are added. The tracking mechanism itself typically uses magnetic field sensors to determine the orientation of the drill string (just behind the drill bit) with respect to the earth’s magnetic field. Knowing this orientation and the distance traveled between measurements, allows the full drill path trajectory to be established. Various adaptations to the basic method are possible – including using an artificially created magnetic field instead of the earth’s magnetic field if sources of magnetic field disturbance are present. Also, the signals from the tracking mechanism at the drill head may be able to be wirelessly transmitted through the ground to the surface. In the so-called “intersect” method to allow very long installations under bodies of water, a homing device may be used at the end of one borehole to allow a tracking device to guide a second borehole to intersect the first borehole at an inaccessible location.

< Return to Guidelines