Telluric currents interfere with cathodic protection systems and cause variations in pipe-to-soil potentials, which can exceed the levels recommended for protection of the pipeline steel. The amplitudes of telluric currents observed in a pipeline depend on three factors: (1) the level of the geomagnetic activity, (2) conductivity of the underlying earth and (3) pipeline electromagnetic properties and geometric parameters. These factors have been incorporated into mathematical models that are used to estimate the pipe-to-soil potential variations due to telluric activity. The time when pipe-to-soil potential variations exceed the recommended level can be different depending on the different telluric activity at the pipeline locations. To evaluate this, a simple model for the telluric electric field has been set up, based on the geomagnetic data and an earth conductivity model. A statistical study based on the long records of the geomagnetic data from Canadian magnetic observatories and conductivity structures of the deep earth allows evaluating telluric activity for 30 years period. In order to show the geographical areas with different levels of activity, a set of maps has been produced and is available through Atlas of Canada web page: http://atlas.nrcan.gc.ca/auth/english/maps/environmentlnaturalhazards/space_weather. The estimated telluric electric fields were used as an input to model pipe-to-soil potential variations on a pipeline. In order to do this, the developed pipeline model has been incorporated to provide an on-line service for different users. The on-line service allows the user to evaluate the pipe-to-soil potential fluctuations at a particular location for a user-defined pipeline.

At extreme latitudes the magnetotelluric method is not generally utilized. This is due primarily to difficulties in making electrical contact with the ground sufficiently well to measure the electric f eld. Because of this, the magnetotelluric technique has not been previously investigated to direct detect gas hydrate in on-shore permafrost environments. The authors present the results of recent field tests at the Mallik gas hydrate production research well site, Northwest Territories that demonstrate good quality magnetotelluric data can be obtained in this environment using specialized electrodes and buffer amplifiers similar to those utilized previously by other workers. This result suggests that subsurface images from larger magnetotelluric surveys will be useful to complement other techniques to detect, quantify, and characterize gas hydrate.

Telluric currents cause variations in pipe-to-soil potentials, which can override a pipeline’s cathodic protection system. The cumulative effect of the “unprotected” time can be significant in areas where telluric activity is high, such as the Canadian north. This paper presents a general approach to the assessment of telluric activity. Telluric currents observed in a pipeline are the result of three simultaneously operating factors: (1) variations of the Earth’s natural geomagnetic field, (2) conductivity of the underlying Earth and (3) pipeline electromagnetic properties and pipeline structure. The first two factors were combined to give an estimation of the telluric electric field that produces variations of the pipe-to-soil potentials in a pipeline. This geoelectric field then can be combined with a particular pipeline equivalent circuit model which gives the pipeline response to the telluric activity in an area. We assess the occurrence of the geomagnetic and telluric activity for a typical year, assuming a general uniform conductivity structure across Canada. A more detailed case study has been done for the auroral zone than spans northern Canada. This includes not only a statistical evaluation of the geomagnetic activity but also specification of regions with different earth conductivities (layered earth structures), which when combined with the geomagnetic evaluation lead to the existence of different regions of telluric activity in the area of investigation. Using results from the assessment of telluric electric fields as an input into the pipeline model, the effects can be interpreted in terms of telluric variations in pipe-to-soil potential.