Department of the Lithology and Geochemistry

Department of Lithology and Geochemistry includes:

• Lithology and Mineralogy Laboratory
• Chemical and Spectral Laboratory

The laboratories carry out a wide range of analytical works on various methods for a large number of geological objects. A particularly large and largely unique experience is accumulated by analyzing various bottom sediments, iron-manganese nodules, sulphide ores. The department has a large fleet of analytical and auxiliary equipment for a full cycle of analyzes, starting with sample preparation. The equipment fleet is constantly being modernized and equipped with new instruments, fr om classical spectral instruments to gas chromatographs and devices for determining the carbon content in the samples. The laboratories are part of the Analytical Center FSBI "VNIIOkeangeologia", certified as an analytical laboratory in accordance with ISO 9001.

In addition to the analytical work, the department actively participates in field work both in traditional regions of the World Ocean and in new water areas, carrying out complex studies and their further geological processing and interpretation.

Currently, the contract with Vietgazprom is being fulfilled.

Further prospects for the development of the department are related to two areas:

1. Introduction of precision methods for studying geological objects, such as ICP spectroscopy and gas chromatography with the expansion of a set of gases - it will allow not only to ascertain the content of individual elements, but also to solve genetic problems.
2. Optimization of the technique of complex gas-hydro-technical survey for various stages of geological survey.
   

The method of marine gas-geochemical survey used in our laboratory allows us to determine the concentrations of hydrocarbon (C₁-C₅) and non-hydrocarbon gases (CO₂, He, H₂, O₂, N₂) in the gas phase extracted fr om the samples of seawater and bottom sediments, and calculate the gas saturation of the samples for each of the listed components.

The extraction of the gas component from water samples and bottom sediments as a part of gas-geochemical research

Degassing of water and bottom sediments provide with a supersonic ejector degassing system "SUOC" and "SUOK-DG". The supersonic ejector developed by the FSBI "VNIIOkeangeologia" staff (patent RU (11) 78 333 (13) U1). The gas sampling method that is used involves a combination of vacuum and supersonic degassing, which ensures a complete separation of the gases contained in the water and bottom sediments, including hydrocarbon fractions. The methodical problem of extracting gases from solid-phase material (bottom sediments) is effectively solved by completely eroding the sample with previously degassed water in a special storage tank of the "SUOK-DG" unit and creating a homogeneous fine dispersion circulated in the system. The velocity of degassing compared to traditional vacuum degassing is reduced from 10-12 minutes to 1-2 minutes in the case of water and 5-6 minutes in the case of the bottom sediments. Heavy manual and unreliable operations to manipulate vacuum valves and buffer solutions are eliminated. The possibility of loading large volumes of the initial material causes the extraction of large volumes of the gas component, which is necessary for some types of analysis. Installations of "SUOC" and "SUOK-DG" successfully proved themselves in operation both in stationary and ship conditions.

Study of the composition of gas samples using a gas chromatograph Shimadzu GC-2014.

Gas-geochemical surveying in the waters of shelf zone with the purpose of searching and exploring oil, gas and gas condensate usually involves studying of the qualitative and quantitative composition of gaseous hydrocarbons C1-C5. The significant excess of the concentration of these components (of which methane is always dominant) over the base level in samples of bottom sediments and bottom water may indicate the presence of gas emanation from the oil or gas deposits in the studied zone. The results of calculating the intragroup balance of the concentrations of some components may indicate of the origin of gases (biogenic, thermometamorphic). 

Analysis of the composition of gaseous hydrocarbons is carried out using a gas chromatograph Shimadzu GC-2014, equipped with a flame ionization detector. Nitrogen is used as the carrier gas. Depending on the work conditions and the performance target, chromatographic columns are used as packed (in combination with an injection valve and injector without a flow divider), and capillary (in combination with an injector equipped with a flow divider and sample injection with a syringe). The chromatographic columns provide less qualitative separation of components, but they are cheaper and they are tolerant to large volumes of samples. The lim it of detection of hydrocarbon components in the gas sample in all cases does not exceed 0.1 ppm.

For the analysis of non-hydrocarbon components (He, H₂, CO₂, O₂, N₂), which is also of great importance for the geochemical exploration of deposits, the gas chromatograph Shimadzu GC-2014 with the thermal conductivity detector is used. The detection lim it of this method for helium and hydrogen, the gases present in the samples in the smallest amount, is 1.5 ppm, which is significantly lower than the equilibrium background concentrations of these components.

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