Prediction of Oil and Gas Occurrence in the Jurassic Reservoirs of the Zone of Junction of the Yenisei–Khatanga and West Siberian Basins

Abstract

Abstract—Based on a comprehensive analysis of the geologic structure, hydrogeology, and hydrogeochemistry, we predict oil and gas occurrence in the Jurassic reservoirs of the zone of junction of the Yenisei–Khatanga and West Siberian basins. We have established the regularities of formation of sandstones of the Sigovaya, Malyshevka, Vym, Nadoyakha, Sharapovka, and Zima reservoirs and examined their poroperm properties. The studied Lower and Middle Jurassic deposits, beginning from the Malyshevka reservoir, are characterized by abnormally high formation pressures with an anomaly ratio of up to 1.92. The Jurassic reservoirs bear weakly alkaline, moderately brackish to slightly saline groundwater of Cl Na, Cl–HCO3 Na, and HCO3–Cl Na compositions with TDS = 3.0–23.3 g/dm3. The low-mineralization connate waters determine an inverse vertical hydrogeochemical zoning in the sedimentary cover of the study region.The research data show favorable conditions for the generation and accumulation of hydrocarbon pools. It is shown that the main criteria for oil and gas occurrence are hydrogeochemical (contents of organic compounds, NH4, B, I, Br, naphthenic acids, and benzene; B/Br and HCO3/Cl coefficients), gas (total gas saturation of formation waters, degree of their gas saturation (Kg), and composition of water-dissolved gases), and hydrodynamic (formation pressures and their anomaly ratio (Ka)) indicators. Also, complex anomalies have been revealed in the Jurassic deposits, which trace the gas fields and revealed oil and gas occurrences.The Jurassic reservoirs are most promising for structure-lithologic traps in the peripheral zones of the basin and on the slopes of large positive structures. The Middle Jurassic deposits in the interior of the Yenisei–Khatanga Basin, poorly studied by deep drilling, might also be of interest as potential hydrocarbon pools.