Survey tools, in terms of trenchless construction, are downhole tools lowered into the hole to check the progress and condition of a bore. These tools include sensors, electromagnetic telemetry, and BHA modules. Sometimes called wireline tools, they can be integrated into the bottom hole assembly (BHA) or introduced into the bore as part of the bore completion process. Survey tools are used to verify that the bore is within the design path in trenchless construction.
A trenchless construction project may include survey tools used by the land surveyor — transits, laser theodolites and other equipment to measure angles and distance. However, the survey tools used in trenchless technology are downhole tools used to ensure accuracy of the bore path.
Each survey tool has a different purpose. Drill string sensors indicate the angle of the bore, the direction in which the bore runs and the orientation of the tool face to the working surface. Electromagnetic telemetry systems transmit data about the path of the drill string and the bore to receivers on the surface, allowing the driller to adjust the drill and maintain the design pathway. Compact BHA modules provide the driller and the project engineer insight into the materials the drill encounters, allowing them to make adjustments as necessary. The BHA module provides directional and geological information based resistance and X-ray measurements.