Transient electromagnetic surveys with unimodal transverse magnetic field: ideas and results
V.S. Mogilatov, A.V. Zlobinskiy and B.P. Balashov
Journal name: Geophysical Prospecting
Issue: Vol 65, No 5, September 2017 pp. 1380 - 1397
Info: Article, PDF ( 14.27Mb )
The theory behind transient electromagnetic surveys can be well described in terms of transverse magnetic and transverse electric modes. Soundings using transverse magnetic and transverse electric modes require different source configurations. In this study, we consider an alternating transverse magnetic field excitation by a circular electric dipole. The circular electric dipole transmitter is a horizontal analogue of the vertical electric dipole. Offshore surveys using circular electric dipole might represent an alternative to the conventional marine controlled-source electromagnetic method at shallow sea and/or for exploring relatively small targets. Field acquisition is carried out by recording either electric or magnetic responses. Electric responses bear information on the 1D structure of a layered earth and successfully resolve highresistivity targets in marine surveys. Land-based circular electric dipole soundings are affected by induced polarisation. On the contrary, magnetic responses are absent on the surface of a 1D earth, and as a result, they are very sensitive to any and even very small 3D conductivity perturbations. In addition, they are sensitive to induced polarisation or some other polarisation effects in the subsurface. At present, circular electric dipole transmitters and magnetic receivers are successfully used in on-land mineral and petroleum exploration.