Downhole reception and transmission of electromagnetic data telemetry signals

A system for receiving electromagnetic (EM) telemetry signals, the system comprising:

• a wireline deployable into a first wellbore comprising a first casing, the wireline comprising one or more electrical conductors extending longitudinally along the wireline from an uphole end of the wireline to a signal pickup on the wireline, the signal pickup comprising a wireline electrode electrically connected to a first electrical conductor of the one or more electrical conductors of the wireline;
• a reel operable to move the signal pickup to a position along the first wellbore,
• a reference electrode;
• and
• an EM telemetry signal decoder connected at the uphole end of the wireline, the EM telemetry signal decoder having an input electrically connected to the wireline electrode by way of the first electrical conductor of the wireline and electrically connected to the reference electrode, the EM telemetry signal decoder configured to monitor a potential difference between the wireline electrode and the reference electrode;
• and
• surface equipment configured to measure a signal to noise ratio (SNR) of the potential difference as a function of the position along the first wellbore and to facilitate deploying the signal pickup at a location in the first wellbore that is determined at least in part by the SNR of the potential difference,
• wherein the wireline electrode is adapted to electrically contact an inside surface of the first casing when the signal pickup is deployed into the first wellbore.