Abstract: Apparatus, systems, and methods may operate to couple a power supply to a ground point associated with a well, and to a lower portion of a conductive casing disposed within the well, where the lower portion of the conductive casing is separated by an insulating gap from an upper portion of the conductive casing, the upper portion of the conductive casing being at a higher elevation of the first well than the lower portion of the conductive casing. Further activity may include injecting an excitation signal into the lower portion of the conductive casing to induce a magnetic field in a geological formation surrounding the first well. Additional apparatus, systems, and methods are disclosed.