Geochemistry of Water-Dissolved Gases of Oil-and-Gas Bearing Deposits in Northern and Arctic Regions of Western Siberia

• Published in: IOP Conference Series: Earth and Environmental Science
• Main Authors: Dultsev, F F, Chernykh, A V
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: IOP Publishing 2020
• Subjects: Arctic; Siberia
• Online Access: http://dx.doi.org/10.1088/1755-1315/459/4/042024; https://iopscience.iop.org/article/10.1088/1755-1315/459/4/042024/pdf; https://iopscience.iop.org/article/10.1088/1755-1315/459/4/042024

Abstract The paper presents a pioneering attempt in the last 35 years, to summarize the accumulated data on geochemistry of water-dissolved gases of oil and gas-bearing deposits in northern and arctic regions of Western Siberia. Water- dissolved gases from all the studied oil/gas fields are characterized by absolute predominance (up to 75-99 vol.%) of the methane series hydrocarbons in their composition. The identified (after the L.M. Zorkin’s classification) four classes of hydrocarbon type of water-dissolved gases (vol.%) are designated as: dry (ΣHH < 1), lean (ΣHH = 1-3), semi-fat (ΣHH = 3-5) and fat (ΣHH> 5). The total gas saturation of groundwaters ranges from 0.3 to 5.7 L/L with CH 4 concentrations averaging 95.5 vol.% in the Aptian-Albian-Cenomanian to 83.3 vol.% in the Lower-Middle Jurassic complexes. The levels of homologues ΣHH (C 2 H 6 , C 3 H 8 , C 4 H 10 , C 5 H 12 and C 6 H 14 ) tend to increase with depth: from 1.34 vol.% in the Aptian-Albian-Cenomanian to 11.67 vol.% in the Lower-Middle Jurassic complex. The maximum ΣHH concentrations reaching 30 vol.% were found at the Neocomian base in the peripheral waters of oil accumulations. CO 2 levels show an increasing trend with depth, whereas N 2 concentrations tend to decrease. Given the increased depths and more severe temperature conditions, the level of hydrocarbon generation remains high, however hydrocarbon series is characterized by a shift towards liquid components and methane homologues (the main zone of oil/fat gases generation). Therefore, the revealed in the Lower-Middle Jurassic complex highly gas-saturated groundwaters (up to 4.5-5.7 L/L) enriched with methane homologues allow to assess their hydrocarbon prospects as very high.