TY - JOUR

T1 - Analysis of water-gas system equilibria in Jurassic-Cretaceous reservoirs (by the example of the Yamal-Kara Depression)

AU - Novikov, D. A.

N1 - Funding Information: The research was conducted with financial support of the Basic Science Research FNI project No. 0331-2019-0025 ”Geochemistry, origin and formation of the chemical constituents of groundwater in Arctic segments of the Siberian sedimentary basins” and from the Russian Foundation for Basic Research, project No. 18-05-70074. Publisher Copyright: © 2020 Publishing House of Siberian Branch of the Russian Academy of Sciences. All rights reserved. Copyright: Copyright 2020 Elsevier B.V., All rights reserved.

PY - 2020/8

Y1 - 2020/8

N2 - The paper presents results of the pioneering study of equilibria in the water-gas system by the example of Jurassic- Cretaceous deposits of the Yamal-Kara depression located within northern West Siberia and its Arctic regions. Numerical modeling of physicochemical equilibria and evasion-invasion processes in the water-gas system allowed determination of the degree of groundwater saturation with gases and the nature of diffusive redistribution of gases in the media that form at the hydrocarbon deposit-groundwater contact. According to the degree of water saturation with gases (Kg), aquifers with poorly (<0.2) to ultimately (0.8-1.0) gas-saturated waters have been established. The revealed increase in the degree of groundwater saturation with gases in sinking producing reservoirs reflects its dependence on their total gas saturation. All waters with a total gas saturation of more than 1.8 L/L become ultimately saturated with gases (Kg = 1.0), thus theoretically predetermining the formation of hydrocarbon accumulations. Major gas condensate deposits are confined to the zone of gas-saturated waters with Kg from 0.8 to 1.0, while oil accumulations, to waters with lower gas saturation. Based on the established nature of water-gas, we can argue that oil and gas accumulations in Jurassic-Cretaceous reservoirs act as a conservative element of the lithosphere, i.e., its geologic and geochemical "relics". The surrounding subsurface waters, as a more active constituent of the system, have largely anticipated its geochemical development, which is manifested in the differentiation of the fugacity ratios of individual gases in groundwater and hydrocarbon accumulations. The composition of the latter is therefore subjected to slow directional changes while the equilibrium is established, to usher in the qualitatively new state of the geochemical water-gas system.

AB - The paper presents results of the pioneering study of equilibria in the water-gas system by the example of Jurassic- Cretaceous deposits of the Yamal-Kara depression located within northern West Siberia and its Arctic regions. Numerical modeling of physicochemical equilibria and evasion-invasion processes in the water-gas system allowed determination of the degree of groundwater saturation with gases and the nature of diffusive redistribution of gases in the media that form at the hydrocarbon deposit-groundwater contact. According to the degree of water saturation with gases (Kg), aquifers with poorly (<0.2) to ultimately (0.8-1.0) gas-saturated waters have been established. The revealed increase in the degree of groundwater saturation with gases in sinking producing reservoirs reflects its dependence on their total gas saturation. All waters with a total gas saturation of more than 1.8 L/L become ultimately saturated with gases (Kg = 1.0), thus theoretically predetermining the formation of hydrocarbon accumulations. Major gas condensate deposits are confined to the zone of gas-saturated waters with Kg from 0.8 to 1.0, while oil accumulations, to waters with lower gas saturation. Based on the established nature of water-gas, we can argue that oil and gas accumulations in Jurassic-Cretaceous reservoirs act as a conservative element of the lithosphere, i.e., its geologic and geochemical "relics". The surrounding subsurface waters, as a more active constituent of the system, have largely anticipated its geochemical development, which is manifested in the differentiation of the fugacity ratios of individual gases in groundwater and hydrocarbon accumulations. The composition of the latter is therefore subjected to slow directional changes while the equilibrium is established, to usher in the qualitatively new state of the geochemical water-gas system.

KW - Arctic

KW - Degree of water saturation with gases

KW - Equilibrium

KW - Fugacity

KW - Hydrocarbon deposit

KW - Modeling

KW - Total gas saturation

KW - Water-gas system

KW - West Siberia

KW - Yamal- Kara depression

UR - http://www.scopus.com/inward/record.url?scp=85093827206&partnerID=8YFLogxK

U2 - 10.15372/RGG2019179

DO - 10.15372/RGG2019179

M3 - Article

AN - SCOPUS:85093827206

VL - 61

SP - 874

EP - 890

JO - Russian Geology and Geophysics

JF - Russian Geology and Geophysics

SN - 1068-7971

IS - 8

ER -