METHOD FOR CARRYING OUT OFF-SHORE GEOELECTRICAL PROSPECTING BY FOCUSING ELECTRIC CURRENT (VARIANTS)

摘要

The invention relates to off-shore geoelectrical prospecting which involves exciting an electromagnetic field in an investigated medium layer by means of rectangular pulses generated by a horizontal dipole source. Said source is towed through a seabed area on one or two rails which are placed in parallel to a measuring rail situated on the seabed and are displaced in an orthogonal direction in respect thereto. The first and second axial and orthogonal differences of electrical potentials and any of four possible segmental electrical potentials between two nearest external measuring electrodes, which are equally spaced from a central electrode along both coordinate axes, are measured. According to measured data, the focusing factors are determined and two interpretable parameters, which are independent of current intensity and the horizontal current density component, are formed at a sounding site, wherein one of the parameters is based on geometrical sounding and the other parameter is based on sounding carried out during transient processes. The parameters are not affected by the lateral effect of three-dimensional geological heterogeneities situated outside of the sounding site. The thus obtained parameters are used for solving an inverse problem according to a differential equation for the electric field strength of a dipole source in an electrochemically polarisable conductive medium, and the electroconductivity, induced polarisation and the decay time constant of the potential difference of the induced polarisation are determined.