Logging in natural γ-ray spectroscopy
Logging in natural γ-ray spectroscopy (NGS) is a technique used in the oil and gas industry to assess the content of specific materials in a specified area. This is achieved by measuring the energy of emitted γ-ray photons from natural sources, such as uranium and thorium isotopes, within a given rock formation. Knowing the abundance and concentration of these isotopes in the formation, the resulting natural γ-ray spectra can be used to categorize and differentiate types of subsurface rock formations (e.g., sedimentary, fractured, or volcanic), to estimate the volume of rock in a given area, to assess the composition of minerals, and to detect oil, gas, coal and other hydrocarbons.
NGS measurements involve the use of a detector, typically a gas detector, that is sent down a borehole to depths ranging from several meters to several kilometers. The detector collects γ-ray photons from natural sources within the rock formation, and the resulting signal is converted into a measured spectrum. The spectrum is then compared to a library of known spectra or to a standard reference sample and used as a basis for interpretation.
The primary purpose of NGS measurements is to characterize rocks and sedimentary layers within a given area. By measuring the amount and energy of the γ-ray emissions, the natural spectral features of various rock types can be identified. NGS can be used to measure grain size and assess material properties, such as porosity and permeability, from the spectral features. It can also be used to detect hydrocarbons and other materials, such as coal, oil, and gas.
In order to accurately interpret NGS spectra, the sources of γ-ray emissions must be accurately identified and their concentrations properly estimated. This is the most challenging part of the process and requires a good understanding of the geology of the area being studied as well as a good understanding of the characteristics of the γ-ray emitters. This involves the use of geophysical and geological data as input in the interpretation process.
NGS data can also be used to provide information on the presence of other materials, such as hydrocarbons, carbonates, and ores, in a specified area. For example, NGS data can be used to detect the presence of oil, gas, and coal in a formation. This data can be used to map out potential areas of oil and gas production and better understand the geology of the area.
In addition to its application in oil and gas exploration, NGS is also used in environmental monitoring, nuclear waste disposal, and other areas where characterizing the contaminants present in a given area is of interest.
In summary, logging in natural γ-ray spectroscopy is a useful tool for characterizing various subsurface rocks, sedimentary layers, and materials. By measuring the energy of γ-ray photons from natural sources, the composition, volume, and other properties of rocks and materials in a given area can be determined. NGS can be used for oil and gas exploration, environmental monitoring, and other areas where contaminants and chemical hazards are of interest.
