HYDROGEOLOGICAL CONDITIONS FOR THE PRESENCE OF OIL AND GAS IN THE WESTERN SEGMENT OF THE YENISEI-KHATANGA REGIONAL TROUGH

Abstract

This article describes the petroleum potential of the Mesozoic deposits in the western segment of the Yenisei-Khatanga regional trough, as assessed from the hydrogeological data. The study area includes the Krasnoyarskregion and neighbouring zones of the Yamal-Nenets Autonomous District (Fig. 1). In tectonic terms, it is confined to the Yenisei-Khatanga regional trough and separates the Taimyr system of tectonic dislocations from the Siberian Platform [ Kontorovich, 2011; Pronkin et al ., 2012 ]. The Meso-Cenozoic section (up to 6–12 km) [ Dolmatova, Peshkova , 2001 ] is limited by the Malokhet-Rassokhin-Balakhnin deep fault and the same name system of mega-ramparts in the east. In the west, it opens up and merges with the structures of the West Siberian megabasin. The hydrogeological materials collected in the study area for almost 40 years, since 1977, remained unconsolidated, and our study did so for the first time. To date, more than 200 deep wells have been drilled in this area, and more than 25 hydrocarbon fields have been discovered. Most geologists acknowledge the leading role of water in the processes of formation, migration, accumulation and degradation of hydrocarbons: water is a medium and an active participant in mass transfer. In this regard, the compositions of groundwater, water-soluble gas and organic matter are widely discussed as hydrogeological criteria that may suggest the presence of oil and gas. The hydrogeological criteria for petroleum prospecting have been classified, and it is now possible to take into account the origin and significance of each indicator, integrate their impacts and attempt at forecasting the regional, zonal and local oil and gas fields. In the Mesozoic section, sodium chloride ground waters predominate. The inversion type of vertical hydrogeochemical zoning is dominant in the study area, and involves the entire complex of deposits: the mineralization decreases from 16–20 g/dm 3 in the Apt-Alb-Senoman complex to 5–10 g/dm 3 or less in the Jurassic aquifers (Fig. 4). The inversion is accompanied by a change in the ion-salt composition of groundwater. The concentration of HCO 3 ion increases with depth; the type of groundwater changes from predominantly sodium chloride (at a depth of ~2300 m) to chloride-hydrocarbonate sodium and hydrocarbonate-chloride sodium. Using the hydrogeological data, we assessed the petroleum potential of the sedimentary cover in the western segment of the Yenisei-Khatanga regional trough. Based on the analysis of the set of criteria and their individual contributions to the overall assessment of the prospects, we have identified 16 highly promising and 20 medium-potential structures that can substantiate further oil-and-gas prospecting, which may discover skipped and new fields. Prospecting can prove highly effective in the Cretaceous reservoirs (Upper Sukhodudinka and Lower Kheta) located in the Nadadyan, Middle Yarov, Tokachin, Turkov, Yarov and other areas (Fig. 6). The Jurassic deposits are promising for small- and medium-sized oil-and-gas reservoirs, as suggested by the geological exploration of previous years, which discovered the Zima (1966) and Khabei (1982) fields. According to the proposed set of the hydrogeological criteria, the most promising among the Jurassic reservoirs is the Malyshev reservoir in the Deryabin, Pelyatkin, Middle Yarov, Tampei and Turkov areas. Promising to a lesser extent are the Sigov (Rassokhin and Sukhodudinka areas) and Nadoyakh (Sukhodudinka area) reservoirs.