Проявление низкочастотной дисперсии электромагнитных свойств земли в измерениях переходного процесса на морских акваториях глубиной до 100 м

Abstract

The article presents a study of the low-frequency dispersion of the geological formations’ electromagnetic properties in transient measurements for the offshore areas with a depth of not more than 100 m. The research methods include calculation and analysis of the transient signal change, the finite difference of the transient signal, and the ratio of the two as a function of the electrical probe immersion depth. The probe consists of a source (a horizontal grounded electric line 500 m long) and a receiver (a three-electrode electric line 500 m long). The study has compared the values obtained at the submerged probes with those obtained at the surface probes. The values for the conducting and polarizable conducting models, obtained at the probes located at the same depth, have been also compared. The base polarizability has been included by introducing frequency-dependent electrical resistivity by the Cole-Cole formula. The calculations have shown a uniform distribution of the transient electric field in the conducting medium at the late stage, the transient signal being the same for the probes located at different depths. For a polarizable model base, the distribution of the transient signal at the late stage is non-uniform, the non-uniformity being a function of the distance to the base. Based on the calculations, it can be argued that with the sea depth of up to 100 m, the low-frequency dispersion of the geological formations for the given model is manifested at the electrical probe with the source length of 500 m on the entire depth range.