Three-Component Downhole TEM Surveys

Conventional downhole EM surveys measure only one component of the EM field aligned with the drill hole axis. Consequently interpretations are often inconclusive. Three-component downhole TEM surveys can overcome the rotational ambiguities associated with current filament inversions. However, suitable probes are difficult to construct. New sensors have now been developed incorporating sensitive preamplifiers. Orthogonal components can be measured sequentially and the orientation of the probe can be determined using an absolute gravity reference. The system has been tested in a ground traverse over a major conductor and the results are consistent with the response obtained using coincident loop techniques.