Mapping Conductivity With Helicopter Electromagnetic Surveys As An Aid To Planning And Monitoring Pipeline Construction

Helicopter EM surveys have been used to map apparent conductivity as an aid to<br>characterizing ground conditions in advance of pipeline construction. The cost of pipeline<br>construction is strongly dependent on the ground conditions encountered, and accurate<br>prediction of these conditions can reduce the planning risk considerably.<br>A DIGHEMV conductivity survey was used to map ground conditions along<br>approximately 130km of prospective pipeline corridor, 400m in width. The survey took<br>four days to complete, providing a map of apparent conductivity with a resolution of<br>approximately 10m. The results are interpreted to determine the extent of shallow<br>bedrock (which would require blasting) and deeper overburden which could be trenched<br>to the depth necessary for the pipeline. Over much of the survey area it is possible to<br>define a single apparent conductivity value as the borderline between soils, which could<br>be trenched, and rock which would have to be blasted. The data can be mathematically<br>inverted to produce maps of the depth to bedrock.<br>The airborne EM survey reduced the time and cost associated with gaining land<br>access and permission for drilling. The survey also served as a check for buried, unknown<br>power lines and pipelines. Airborne EM surveys have also been used to map ground<br>conductivity after the pipelines have been constructed to detect areas of high ground<br>conductivity due to clays or saline soils. These soils can create conditions in which<br>pipeline corrosion is accelerated.