FIELD: physics; geophysics.
SUBSTANCE: invention relates to geophysics and can be used in prospecting for oil and natural gas deposits. Disclosed is an electromagnetic array configured for use in an underground borehole. The array includes a plurality of axially spaced electromagnets and is configured to generate a magnetic field pattern having at least first and second pairs of magnetically opposing poles. Passive ranging measurements of the induced magnetic field may be advantageously utilised, for example, to survey and guide continued drilling of a twin well. The electromagnetic array may also be used in active ranging. An array of permanent magnets providing a similar magnetic field pattern may also be used in active ranging.
EFFECT: high accuracy of survey data.
3 cl, 15 dwg
