MARINE GEOLOGICAL ELECTRICAL EXPLORATION WITH ELECTRIC CURRENT FOCUSING

摘要

The invention relates to marine geological electrical exploration with the use of a dipole source of rectangular current pulses. The measurements are carried out by means of a measuring device consisting of five electrodes, i.e. a central electrode and four electrodes disposed around it at the summits of a square, the opposite sides of which square are positioned in parallel to the axis of the profile. Geometrical sounding is carried out along the profile during a pulse, sounding on transient processes being carried out during a dead time. The electric potential difference between the external electrodes and the central electrode and the electric potential difference between three pairs of the external electrodes are measured. While the dipole source passes through differ points, the equipotentiality of a closed line, which passes through the four external electrodes of the measuring device, is provided, thereby excluding the horizontal current density component jxy inside said line at each sounding site. Two standard interpretable electric parameters, which are not susceptible to the lateral influence of three-dimensional geological inhomogeneities situated beyond the sounding site, are calculated according to the values of the measured electric potential differences. The thus obtained parameters are used for solving an inverse problem on the basis of a differential equation for the electric field strength of the dipole source in a medium, the medium model is defined and the time sections for said model are built according to the electroconductivity of the sections, the coefficient of the induced polarization thereof and the decay time constant of the potential difference of the induced polarization.