The concept of the development of geochemical prospecting is based on a systematic, comprehensive study of the geophysical and geochemical indicators of the sedimentary section, based on their relationship and interdependence in space and time, and is most clearly manifested in the phenomenon of paragenesis of zonal-ring-shaped anomalies of geochemical and geophysical fields over hydrocarbon deposits.
The methodological basis of geochemical methods is the repeatedly established fact of the existence of dispersion halos of hydrocarbon gases (bitumen) and re-altered rocks above oil and gas deposits, recorded in near-surface sediments, in water and air in the form of gas-hydrogeochemical, lithogeochemical, phytogeochemical, bituminous and other anomalies … In a generalized form, the geological – geochemical model of hydrocarbon deposits and dispersion halos according to A.V. Petukhov is presented in the form of zonal – ring-shaped anomalies of geochemical indicators. In practice, depending on the geological and tectonic structure of the sedimentary section, the type of reservoirs and the nature of their saturation, various dispersion halos are observed. Thus, for the south of the Siberian platform, 4 types of hydrocarbon dispersion halos have been identified, differing in morphology by their position in the section: circular, linear – banded, arched, combined.
A – geochemical anomalies (a-helium, б-HC-gases, в-liquid HC, г-biochemical indicators);
Б – generalized lithogeochemical section for anomalous objects and geochemical zones (I-IX)
A scientifically substantiated forecast of oil and gas content can only be carried out on the basis of a comprehensive study of the geophysical and geochemical indicators of the sedimentary section, because geochemical and geophysical fields are characterized by interconnection and interdependence in space and time, and most clearly manifested in the phenomenon of paragenesis of zonal-ring-shaped anomalies of geochemical and geophysical fields over hydrocarbon deposits. The need for the mandatory use of geochemical studies in combination with geophysical work is that the material composition of rocks and the fluids that include them, as well as their features, predetermine changes in the physical properties of the sedimentary section.
The methodological basis of geochemical methods is the repeatedly established fact of the existence of scattering halos of hydrocarbon gases (bitumen) and authigenically altered rocks over oil and gas deposits recorded in near-surface sediments (soil, soil, rocks), in water and air in the form of gas geochemical, hydrogeochemical, biogeochemical, lithogeochemical, phytogeochemical, bituminous, radioactive and other anomalies. The latter are objects of mapping and study by land-based geochemical and geophysical methods.
Field and analytical work methodology
The complex of geochemical studies includes: carrying out field geochemical works, as well as laboratory chemical and analytical studies and cameral processing of the obtained factual materials by the method of graphic constructions together with the results of geological and geophysical studies.
Field geochemical work
Performed in the summer in the form of a comprehensive hydro-gas geochemical survey of surface water sources and free gas outlets. The work is carried out along the river network and includes: water-gas (RUVG, O2, N2, CO2, H2, He), hydrochemical (mineralization, salt composition, VROV, Br, H2S, pH, Eh) sampling of surface waters.
- The bulk of geochemical research is carried out in the winter, together with geophysical work, seismic and electrical exploration (ZSB, DNME). The methodology and technology of geochemical works together with seismic prospecting were tested as a result of experimental and methodological studies carried out by Irkutsk State University together with PGO Irkutskgeofizika. The complex of geochemical sampling includes sampling of cuttings and bottomhole air (sorbed gases) from seismic and explosive wells. In contrast to foreign technologies (passive “hot sorber” method, USA), the developed technique is an “active hot sorber”, which allows more efficient and rapid forecasting of oil and gas content. The technique used allows the study of dispersed gases of closed (HZP cuttings) and open pores (freely released at the bottom of the wells) of the rocks. Sludge samples are subjected to thermal vacuum (mechanical) degassing to determine RUVG, CO2, H2, N2, O2 and crushing-sieve analysis to determine Corg., CBA, heavy metals, carbonates and physicochemical parameters.
Geochemical studies of deep well sections
One of the effective methods for studying well sections is geochemical research (geochemical logging): gas, bituminous, lithogeochemical. The most widely used is gas logging, the resolution of which allows, based on gas saturation and component composition of hydrocarbon gases of rocks, waters and drilling fluid, to carry out operational analysis and assessment of sedimentary deposits exposed by drilling. The GTI operational control stations used in recent years only make it possible to qualitatively assess the exposed deposits, since the gas-logging instruments included in the station have low sensitivity (10-3% vol.), Record a narrow range of combustible gases: paraffin hydrocarbons from methane to hexane and hydrogen.
Therefore, in the difficult geological conditions of Eastern Siberia, there is an acute issue of a detailed and deep study of the gas component of rocks based on the use of more effective methods – thermal vacuum degassing of flushing fluid, thermal desorption of sludge and core using modern gas-liquid chromatographs, which allow for the most complete extraction and study of gaseous and liquid naphthides in a wide range – from methane to decanes and higher, including isomers, normal and cyclic compounds. The latter make it possible to more reliably evaluate and identify oil and gas saturation intervals, as well as to determine the phase and component composition of the formation fluid before opening, during opening and after opening potentially productive deposits. We use the technology of sampling and analysis of lifespan samples, which allows us to obtain reliable information about the composition of formation fluids, using all the geochemical information obtained during drilling. So, in the gas measurement of the pancreatic fluid, mainly the gases of open pores and cracks are investigated. The share of closed pore gases, which carry the most reliable and complete information on the composition of formation fluids and dispersed hydrocarbons, is insignificant. Such information is supplemented on sorbed gases of rocks (gases of closed pores and occluded by a mineral matrix), as well as on dispersed naphthides (bitumen) and lithogeochemical parameters.
Our company performs in deep wells:
- sampling of flushing fluid (cuttings) and, if necessary, core samples
- thermal vacuum degassing of samples of flushing fluid (sludge) and formation water
- mechanical degassing (MD) of core (sludge)
- thermal desorption of cuttings and core samples
- express analysis of the chemical composition of gases of flushing fluid (sludge) and formation water
- determination of the component composition of the pancreatic fluid gases, cuttings, core samples and formation fluids
- determination of the chemical composition and physicochemical properties of formation water
- luminescence-bituminological analysis of cuttings and core samples
- determination of organic carbon in core (sludge)
- lithogeochemical studies of samples of drilling fluid, cuttings and core samples
- determination of petrophysical parameters of reservoir rocks