Petrological dissecting of the section of volcanogenic deposits based on well-logging

Quantitative criteria for identifying petrotypes in the volcanic deposits sections of the pre-Jurassic basement of the Krasnoleninsky arch of Western Siberia are proposed. Petrological dissecting of the pre-Jurassic deposits section based on well-logging data is a priority task, as it enables to establish the most promising petrotypes and create a basis for the subsequent allocation of reservoirs, estimation of the void space type and filtration-capacitive parameters. The studied deposits are dominated by acidic volcanites. Other types of rocks can be identified based on their natural radioactivity, measured using gamma ray logging. The physical basis of the complexation is the natural increase in density and decrease in natural radioactivity from acidic volcanites to medium and basic ones. The natural radioactivity and density of volcanic-sedimentary rocks depend on the ratio of sedimentary and volcanic material. In the sections of volcanic deposits, there are intra-formationary terrigenous rocks (mudstones, siltstones, sandstones, etc.), characterized by a decrease in natural radioactivity and an increase in density compared to acidic volcanites. The identification of secondary transformations can be performed using the parameters M, N, P, weakly dependent on the porosity coefficient and explicitly reflecting the influence of the material composition, as well as the void space features (fracturing and cavernosity). The separation of lavas and volcanic rocks is performed by the values of the porosity coefficient. Characteristic ranges for the porosity coefficient values for lavas of massive texture, lavas with voids and volcanic rocks are established. The boundaries between these groups are respectively 5-6 and 17 %.

References

1. Kropotova E.P., Korovina T.A., Romanov E.A., Fedortsov I.V., Sostoyanie izuchennosti i sovremennye vzglyady na stroenie, sostav i perspektivy doyurskikh otlozheniy zapadnoy chasti Surgutskogo rayona (Rogozhnikovskiy litsenzionnyy uchastok) (The state of knowledge and modern views on the structure, composition and prospects of pre-Jurassic deposits of the western part of the Surgut region (Rogozhnikovsky license area)),Proceedings of IX scientific and practical conference “Puti realizatsii neftegazovogo potentsiala KhMAO” (Ways of realization of oil and gas potential of KhMAO), Khanty-Mansiysk: IzdatNaukaService Publ., 2006, pp. 133–146.

2. Maleev E.F., Vulkanity (Volcanics), Moscow: Nedra Publ., 1980, 240 p. 

3. Dakhnov V.N., Geofizicheskie metody opredeleniya kollektorskikh svoystv i neftegazonasyshcheniya gornykh porod (Geophysical methods for the determination of reservoir properties and oil and gas saturation of rocks), Moscow: Nedra Publ., 1985, 310 p. 

4. Dobryden S.V., Kornev V.A., Semenova T.V., Petrological separation and interwell correlation of volcanogenic rocks (In Russ.), Neftyanoe hozyaystvo = Oil Industry, 2021, No. 6, pp. 38–42, DOI: https://doi.org/10.24887/0028-2448-2021-6-38-42