Abstract: Techniques involve determining the conductivity profile of a formation from a well between a surface location and a borehole location. The method involves placing a first sensor at the surface location, a second sensor located at the borehole location, obtaining a first signal by detecting Schumann resonances from the electric field occurring at the first location, obtaining a second signal by detecting Schumann resonances from the electric field occurring at the second location with the second sensor; and combining the first and the second signal to determine the conductivity profile of the formation between the first location and the second location.

Abstract: Techniques involve determining the conductivity profile of a formation from a well between a surface location and a borehole location. The method involves placing a first sensor at the surface location, a second sensor located at the borehole location, obtaining a first signal by detecting Schumann resonances from the electric field occurring at the first location, obtaining a second signal by detecting Schumann resonances from the electric field occurring at the second location with the second sensor; and combining the first and the second signal to determine the conductivity profile of the formation between the first location and the second location.

Abstract: A downhole electromagnetic telemetry unit for use with a tubing string (5) includes an insulated electrically conductive member (31) and a processing unit (15). The insulated electrically conductive member (31) is electrically coupled to the tubing string (5) at an upper measuring point (23) and a lower measuring point (25). The processing unit (15) is configured to process a voltage difference measured between the upper measuring point (23) and the lower measuring point (25) across the insulated electrically conductive member (31) and to derive therefrom a signal transmitted from a surface location (13).