About Wireline Surveying

Drillhole surveying is the process of the delineation of the path of a bore hole relative to a known start position

When a bore hole is drilled in the earth (or even large concrete structures such as dams), deviation from the initial start point will always take place. This can be relatively minor for short, large diameter holes or extreme for long small diameter holes. In some cases holes may be deviated intentionally to intersect a particular underground target.  Where information is being extracted from drill holes for the delineation of ore bodies and geophysical modelling or the hole has been drilled for an engineering purpose such as a blast hole, it is extremely important to know its path. To achieve this many systems have been developed to survey the deviation of bore holes

Most modern systems consist of an instrument encased in a protective pressure barrel lowered into a bore hole which takes discrete measurements of the inclination and direction of the hole at known depths. From this information (depth, inclination and direction) the co-ordinate position can be deduced relative to the top of the hole or the local map grid.

Surtron Technologies uses two main methods for Drillhole survey purposes; one is a gyroscopic method and the other magnetic based.

Magnetic type systems use either a compass (very simple systems) or solid state fluxgate magnetometers to determine direction. Using the Earth's magnetic field for determining direction is fast and relatively accurate, however magnetic anomalies either in the surrounding rock formation or generated by the drill string can have a marked effect on the accuracy of such systems.

Gyroscopes have been used to survey drill holes since the 1930s, they offer accuracy and are impervious to magnetic anomalies. Gyroscopes can be used inside a steel drill string with no detriment to accuracy. Surtron Technologies uses gyroscopes referenced to the local geographic grid system or in north seeking form.

In general, gyroscopic surveys are preferred by the mining and petroleum industries due their inherent accuracy, flexibility and in the right application speed of operation.