Vol 61 Iss. 2

Assessment of the degree of similarity or difference of geological structures has always been of interest to researchers, as it has practical implications: questions of the genesis of structures and predictions of the distribution of mineral deposits are largely solved taking into account possible analogies. The complexity of this assessment is compounded by the fact that natural objects, unlike the products of human technological activity, are in their individual features necessarily unique. Even in the simplest cases, one can reasonably expect some difference between nearby structures having the same origin. A significant difficulty is the selection of those indicators (attributes) by which the degree of closeness of the compared geological structures is assessed. Heightened interest in certain aspects (genesis, ore content, metamorphism, etc.) may manifest itself in the fact that some features will subjectively receive greater importance than others, while some will be entirely omitted from the analysis.

Based on the vast experience of seismic exploration in oil- and gas-bearing areas, the methodology and systems of observations using reflected and refracted waves as applied to the study of gentle structures of sedimentary rocks have been well developed and are still being improved. At the same time, in recent years, the seismic exploration method is increasingly used to study the consolidated crust and, in particular, structures composed of highly metamorphosed and crystalline rocks in regions where ore deposits are being explored for. Under these conditions, seismic exploration is tasked with studying very complex folded and highly dislocated structures formed by rocks that are relatively poorly differentiated in terms of elastic wave propagation velocity.

The search for ore bodies of enhanced electrical conductivity by the method of dipole inductive profiling with amplitude-phase measurements is based on the study of changes in the magnetic field of a harmonic magnetic dipole as a function of its movement along the profile (relative to the ore body).

Precambrian platforms and shields, occupying the main part of the territory of the continents and containing in their interiors huge reserves of minerals, have been insufficiently studied geologically. The subdivision and correlation of Precambrian strata by classical methods of paleontological, petrographic and structural-geological analysis are extremely difficult, because deeply metamorphosed and granitized rocks in many cases retain only relict textural-structural and lithological features of the original geological formations. Geophysical methods, in particular gravity and magnetic exploration, have great potential for studying the structure and reconstructing the development history of Precambrian shields.

The existing methods of determining the parameters of geological objects from gravity anomalies are based on the approximation of the original data by analytical expressions, the parameters of which are subject to determination.

As is known, electrical exploration methods identify well-conducting objects, which can be both sulfide bodies and graphitized zones or zones of tectonic faults. While the latter can often be identified using amplitude and phase components of the eletromagnetic field during dipole profiling, it is still impossible to separate anomalies associated with sulfide ores from those associated withgraphitized zonesby means of electrical exploration.

Under dipole inductive profiling (DIP) is understood a sequential study of the amplitude and phase of the magnetic field of a harmonic magnetic dipole, performed with simultaneous movement of the dipole generator and dipole-measuring device (measuring point) along a certain direction (profile) on the surface of the earth. The reciprocal spatial position of the dipoles (generator and receiver frames) is kept constant during profiling, so the relative field changes at the measurement points are only a function of the geoelectric cross sections of the areas traversed by the installation. ...

The advantage of dipole inductive profiling (DIP) is the optimal relationship between the transmitter, receiver, and the target object, which is technically easy to implement. At the same time, a depth practically comparable in many cases with other inductive methods is achieved through the use of simplified portable equipment, which allows to significantly increase the productivity of electrical prospecting.

The industrial oil-shale bed of the Leningradskoye field is confined to the Kukruse horizon of Ordovician limestones. The thickness of the overlying strata varies from 50-60 m in the north to 80-100 m in the south. In the northern part, Ordovician limestones occur directly under Quaternary sediments; in the southern part, in addition to Quaternary sediments, they are overlain by Middle Devonian sediments (marls, sands and clays). The thickness of Quaternary sediments is on average 5-10 m.

The method of borehole magnetic exploration is currently used almost exclusively for magnetite deposits of various genetic types. There is practically no experience in applying this method to relatively weakly magnetic objects. This is explained mainly by the insufficient resolution of modern borehole magnetometers, which do not allow measuring the magnetic field in the borehole with an accuracy higher than ± (1000–1500) gammas for the full field vector and 500 gammas for its vertical component.

One of the important tasks of borehole logging in ore districts is the delineation of ore intervals and determination of the metal content in the ore. At the sulfide copper-nickel deposits of the Pechenga region, a complex of geophysical methods can now confidently distinguish only the zones of sulfide mineralization with which the ores are associated. ...

Significant volumes of drilling in prospecting and exploration of copper-nickel ores within the Pechenga and Alla-Akka-Yarvinsky ore fields lead to constant efforts aimed at improving borehole logging and increasing its efficiency. To date, the issues of integrating standard logging methods have been solved and the possibilities of both the complex as a whole and of individual methods for identifying the main types of rocks and ores have been clarified.

Vertical seismic profiling (VSP) in the wells of the Pechenga region is carried out under conditions of steep dips of geological boundaries, and the wells themselves are deviated (zenith angles of 5–20°).

In 1968, a seismic station with intermediate magnetic recording — POISK-1-48-KMPV-OV — was introduced into the practice of regional seismic work on the Baltic Shield. The use of magnetic recording made it possible to analyze seismic data in laboratory conditions for the purpose of deciphering interference sections of the wave field and for more reliable correlation of the main waves in the interference zones.

Seismic data obtained during detailed studies in the Pechenga district of the Murmansk region are characterized by the presence of a large number of short coherent axes, from which subsequently reflecting elements are constructed by the apparent-velocity method. ...

In the joint application of several geophysical research methods, an approach is widely used in which, on the basis of data from individual methods, special corrections are calculated and applied to the readings of other methods. This significantly increases the detail and reliability of the overall conclusion about the identified features of the geological structure. ...

The specificity of the problem under consideration is that the analytical expressions for the Za and ΔT fields include not the dip angles themselves, but some auxiliary angles (respectively, ν and ε), which depend not only on the direction and dip angle, but also on the inclination of the magnetization vector and the strike azimuth of the bed.

In permeable rock formations, natural filtration of formation water can be observed, corresponding to its movement from the recharge area to the discharge area. If a well intersects such rocks, this phenomenon affects the temperature regime of the medium within it.

Stationary filtration of groundwater affects the thermal state of rocks and creates an anomalous temperature distribution in wells. The amplitude of the temperature anomaly on such geothermograms recorded in wells under a steady-state thermal regime can be used to calculate the filtration rate in the aquifer by means of formulas...