Выпуск: 7 , Том: 63 , Год издания: 2022

Electrical measurements in water areas, as well as on land, are carried out to study the electromagnetic (EM) properties of geologic objects. The specifics of aquatic electrical prospecting are associated with the specific influence of a water column. We present numerical calculations of the EM signal of the transient process for electrical lines in the axial region of the source in 50-250 m deep sea waters in order to demonstrate the manifestation of induced polarization (IP) in the transient-process signal at different setups, to reveal the differences in the manifestation of galvanic (GP) and double induced (DIP) polarization in the transient-process signal, and to explain the causes of these differences. To study the influence of the size of the setup on the manifestation of IP during the transient process, we analyzed the changes in the signal of the transient process (ΔU(t)), in the finite difference between the signals of the transient process (Δ²U(t)), and in the transform P1(t) (the ratio of these values) for a horizontal electrical setup with a 50 to 2000 m long source (AB) and a 50 to 2000 m long three-electrode measuring line (M₁M₂M₃) and with the distance between the centers of the source and the measuring line M₁M₃ (spacing, r) from 100 to 4000 m. Some of these parameters are used in differential-normalized electrical prospecting (DNEP). Comparison is made for ΔU(t), Δ²U(t), and their transforms in the conducting and conducting polarizable models under the same conditions. The setup was placed on the surface and inside a conducting medium (a sea shelf water column) with a conducting polarizable base (geologic medium (earth) covered with a water layer). The polarizability of the base was taken into account by introducing a frequency-dependent resistivity, using the Cole-Cole formula. The performed calculations show that the components of the transient process that are associated with the formation of the EM field and with GP and DIP manifest themselves in different ways at setups of different sizes at different depths. In water area, IP manifests itself in two ways, being associated with both galvanic and eddy currents. In previous practical measurements, DIP was considered to be associated with interference, but this signal is simulated and can be regarded as the information about IP. The factor influencing the IP manifestation in the transient-process signal is the reduced setup height (hΔ), i.e., the distance between the setup and the sea bottom (the polarizable base of the model) referred to the AB length. Depending on the reduced setup height, the IP signal in the transform P1(t) can manifest itself as an ascending branch at later times or can appear as a descending branch passing into the negative values of P1. The duration of the pulse impact and the measurements of the transient process affect the contrasting manifestation of the polarizable base in the signal, but the measurements under setup towing impose certain restrictions. The optimal parameters of EM survey for studying IP should ensure a sufficient polarization range and the proper quality of measurements. The software used in the calculations was developed by OOO Sibirskaya Geofizicheskaya Nauchno-Proizvodstvennaya Kompaniya.