Marine geochemical exploration
In the search and exploration of oil and gas in the seas (shelf), as well as in lakes (reservoirs), the main geochemical method is gas geochemical surveying in the near-bottom waters and bottom sediments in which, as a result of sub-vertical migration of hydrocarbons from oil and gas deposits (gas hydrate strata), geochemical anomalies. The presence of oil and gas deposits is recorded in seawater and bottom sediments in the form of gas-geochemical, lithogeochemical, bituminous anomalies in which the content of hydrocarbon compounds (liquid and gaseous) many times exceeds their background concentrations. The most contrasting geochemical anomalies are recorded in the bottom waters above the zones of active faults and permeable sections of the sedimentary section, most often in methane, its homologs, hydrogen, carbon dioxide, helium, especially if the faults are located within the oil and gas-bearing strata.
The production technologies of the offshore GPNG include regional and prospecting-and-evaluation oil and gas exploration of the water areas using a litho and gas survey in conjunction with seismic and electrical prospecting (DNME) works. When carrying out engineering and geological surveys at the stage of preparation of sites for deep exploratory drilling, detailed gas geochemical sampling of bottom sediments using sorption tubes and bottom grabbers is carried out. Also, in the study of high-water areas, detection of gas hydrate and permafrost sequences, point geochemical studies are used for bottom stations and core wells.
The tasks of geochemical research in the water areas include:
- The sorting, ranking, and classification of local objects, identified by geophysical methods, according to the degree of oil and gas potential;
- operative assessment of oil-prospecting zones and local facilities based on express analysis of bottom-water gases from the bottom of the vessel using portable gas chromatographs;
- seismic and electrogeochemical forecast of the oil and gas potential of the sedimentary section based on the complexation of seismic prospecting (2D), electrical prospecting of DNME, and geochemical studies;
- outlining the hydrocarbon deposits with the determination of the saturation nature of the productive strata, the separation of the GVK (VNK), the zones of the wedging of the reservoirs;
- Isolation and delineation of gas hydrate and permafrost sequences, allocation of dehydration and thawing sites in them;
- mapping of tectonic disturbances (TOZ) with the determination of their fluid permeability;
- geoecological research in geophysical and drilling operations;
- a detailed study of bottom sediments by litho- and gas-geochemical testing in the production of engineering-geological surveys