Radiometric studies are carried out on near-surface sediments in combination with lithological, gas and geochemical, and hydrological gas and geochemical methods, usually on shallow boreholes, holes, or “pits”. Radiometric methods include gamma surveying and radonometry (on soils and surface water).
Radiometric studies are aimed at forecasting oil and gas content, delineating hydrocarbon accumulations and GWC (OWC), zones of lithologic pinch out of reservoirs, mapping tectonic disturbances, and assessing their conductive and screening properties. In the latter case, along with the radiation parameters, indicators such as radon, helium, hydrogen, nitrogen, carbon dioxide, and oxygen are used. Gases of this group have a high migration ability. The first of them is characterized as a “geo-indicator” by a peculiar (short) half-life of a stable isotope (only 3.8 days). It is of practical importance for the indication of geodynamic processes. The presence and activeness of tectonic disturbances and deconsolidation zones are determined by the high concentration of radon in the near-surface layers. The highest radon concentrations correspond to the most permeable sections of snaps and deconsolidated zones and serve to:
- confirm tectonic disturbances revealed by seismic and electrical reconnaissance data and map ground surface outputs of tracing weakened zones;
- differentiate tectonic disturbances into “open” and “healed”;
- differentiate “open” tectonic disturbances into “constantly open” and time-varying;
- identify conditions for the contact of tectonic disturbances with pay zones;
The integration of radiometric and geochemical methods allows more reliable contouring of especially tectonically shielded hydrocarbon accumulations, delineation of tectonic disturbances, and evaluation of their activeness, conductive, and shielding properties.
It has been established that during migration, hydrocarbons have a restoring effect on the host rock with the formation of an adsorption layer on the surface of clay rocks, which makes ion exchange difficult between solid phases of rocks and the environment. Precipitation of uranium compounds occurs most intensively in a reducing medium in the presence of OM (humic acids, carbonaceous impurities) and sulfides. High concentrations of uranium are characteristic for waters with positive reduction potential values. At the same time, oxygenated waters have increased uranium content, while hydrogen sulfide waters are heavily depleted (R.P. Gottikh, 1980).
The content of uranium in rocks reveals its relationship with oxidized forms of naphthides, including dispersed bitumen and alcohol-benzene tars (Pisotskiy and Pastukhov, N, P., 1988).