The Kimal Converter Substation - The Challenges of Geoelectric Modeling in a Desert Environment

This paper presents the challenges of geophysical surveys and geoelectric modeling for the grounding grid design of the future Kimal Converter Substation, to be built in the hyperarid

Atacama Desert, in the northern area of the Chilean Central Depression.

The surficial ground is known as Caliche, a cemented layer of carbonates and sulfide sediments with very high electrical resistivity, which forms in arid and semi-arid regions where evaporation exceeds precipitation. Below the caliche, the resistivity drops significantly due to subsurface salt deposits. Three geophysical sounding methods were applied:

• electrical survey – 3 ERT (electroresistivity tomography) profiles, probing the shallow ground (tens of meters), from which were extracted 3 sets of Vertical Electrical Soundings

(VES) with Schlumberger configuration; and

• near-surface electromagnetic survey – 4 collocated AMT (audiomagnetotelluric) and TEM

(time-domain electromagnetic) soundings, probing the deep ground (hundreds of meters).

ERT and AMT geophysical sounding methods require measurements of the electrical fields at the soil surface; therefore, both are affected by static shifts, a consequence of near-surface inhomogeneities. The data processing required filtering and adjustments to account for deviations introduced by high contact resistance and high contrasts in subsurface resistivity.