METHODS
The induced polarization (IP) method is an extension of the electrical resistivity method. It’s based on additional measurement of the “capacity” of a geological medium to collect electrical charges. The IP method is used in deep and medium-range prospecting geophysics, for mapping of metallic ore deposits. The method is also gaining popularity in oil exploration in determining the contours of the deposit.
The individual elements of the geological medium, as a result of the polarisation of the induced electric impulse, generate a time-dependent decaying electric current which can be recorded at the ground surface, once it is switched off. Making reliable measurements is due to the fact that the objects of interest generate signals of different amplitudes and signal fading times depending on the structure and mineral composition of the geological medium. The effect of excited polarisation is strongest for the electron-conducting minerals found en masse in metal ore deposits. In contrast, fresh waters show a lack of pulse polarisation.
The chemical processes associated with the diffusion of hydrocarbons in a diffusion stack can, under certain conditions, lead to the formation of diffuse electron-conducting sulfide mineralization in the near-surface zone. This phenomenon gives rise to the application of the IP method in the exploration and mapping of hydrocarbon reservoirs by being able to determine the extent of the diffusion stack (or more precisely the associated pyritization zone). The boundaries of the reservoir are further indicated by anomalous polarisation parameters associated with filter potentials in the water-petroleum contact zone.
