Application possibilities of IP method in the fields of environmental protection, ore- and direct hydrocarbon exploration

From the 1950s the induced polarization (IP) method became well known as an effective geophysical method of ore exploration in the geophysical literature [1–3]. It was applied successfully in ore exploration both in time-domain (TDIP) and frequency-domain (FDIP) measurements, because the metallic polarization phenomenon can occur on the surface of ore showing conductive (free electronic) electric conduction – in a dissociated ionic environment. This type of polarization causes measurable IP anomalies. On the other hand, the metallic content is not the only factor resulting in polarizability of the medium: filtration- and membrane effects as well as electrochemical (redox) properties can also lead to similar phenomena. Due to recognition of this, nowadays the IP method has turned into one of the most efficient geophysical methods for environmental investigations. In electromagnetic geophysical practice [4], however, it is also known that pyrite chimneys may be formed in the roof of productive (containing crude oil, or natural gas) hydrocarbon reservoirs, which causes metal polarization. The ring-like IP anomaly over hydrocarbon reservoirs may be an important feature of productivity in direct hydrocarbon explorations. Time constant analysis means a novel opportunity of application in all three areas (environmental protection, ore- and direct hydrocarbon exploration). The time constant spectrum of the IP signal can be calculated with TAU-transformation [5]. Anomalies appearing in the interval of the short time constants (smaller than 1 sec) can be bound to less dangerous environmental effects (filtration and membrane), while the larger (higher then 1 sec) time constants connected to dangerous polarizations (redox and electrode) indicate chemical and metallic contamination. Analysis of the interval of high time constants makes it possible to define the types of ores and the pyrite chimney above the borders of productive hydrocarbon reservoirs.