Stratigraphy, Sedimentology and Geochemistry of the Oligocene – Lower Miocene Maikop Group in Dagestan, Ne Caucasus

Exploration efforts around the Greater Caucasus region started towards the end of the 19th century and established a wide range of petroleum play types in various basin segments around the orogen. All these plays are associated with the flanks of the inverted thrust-fold belt and the adjacent foreland basin systems, but display significant variation among the basin segments depending on the tectonostratigraphic units involved and the degree of exploration maturity. Whereas the same main source rocks have generated most of the hydrocarbons in all the basins (namely organic-rich shales in the Oligocene -Lower Miocene Maykop Group and the Eocene Kuma Formation), it is primarily the trapping style, both proven and speculative, which is responsible for the broad spectrum of play types observed. Eleven play type diagrams across six main petroleum provinces of the Greater Caucasus region are presented in this paper and summarize the current exploration understanding of the existing discoveries and potential new play targets. These play cartoons offer a prospect-scale summary of both mature producing and underexplored basin segments in a coherent visual manner, and are therefore intended to promote future exploration efforts in the Caucasus region. The testing of new play types requires the proper risking of the two most critical elements in the region: hydrocarbon kitchen effectiveness, and post-charge trap modification. The de-risking of these factors will require properly designed, fit-for-purpose acquisition of modern geological and geophysical data sets.

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Geochemistry of Oils in the Terek‐caspian Foredeep and Prikumsk Swell, Ne Greater Caucasus, Southern Russia

Yandarbiev

Sachsenhofer

Ajuaba

et al. 2021

Journal of Petroleum Geology

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Hydrocarbon reserves of the order of 1140 MM brl oe have been identified in the northern foreland of the eastern Greater Caucasus, principally in the Terek-Caspian fold-and-thrust belt and the Prikumsk Swell in the north of the Terek-Caspian foredeep. Despite the great economic significance of these areas and their long exploration history, the origin of the hydrocarbons is still poorly understood. In the present paper, geochemical data from 73 oil samples representing 28 fields are used to investigate the presence of oil families and to correlate the oils with potential source rocks.Biomarker composition of oils in Cretaceous and Miocene reservoirs in the Terek-Caspian fold-and-thrust belt is mainly controlled by reservoir depth (100-5700 m) and maturity (0.70-1.15 %R o ), and it is therefore difficult to separate maturity and facies effects. For example, a downward increase in diasterane/sterane ratios may indicate a change in source rock facies or may be attributed to increasing maturity. Some shallow oils are biodegraded. The presence of short-chain n-alkanes in biodegraded oils indicates recent hydrocarbon migration. Biomarker data (e.g. the presence of oleanane) and compound-specific isotope data suggest that the Khadum Formation in the lower part of the Maikop Group is the main source rock. However data from Cretaceous and Paleogene organic-rich rocks, which may also have contributed to the accumulated oils, are urgently needed in order to quantify their possible input.In the Prikumsk Swell, at least two oil families, characterized by low and high C 28 /C 29 sterane ratios respectively, can be distinguished in reservoir rocks of Triassic to Cretaceous age. Most oils are characterized by low C 28 /C 29 sterane ratios and the absence of oleanane ("Group B oils"). These characteristics suggest a pre-Upper Cretaceous source for the oils, which is also supported by the geological setting. Hierarchical cluster analysis suggests the presence of four sub-groups (Sub-Groups B1 to B4). Typically, biomarker ratios in oils in Cretaceous reservoirs are more uniform than those in Triassic and Jurassic reservoirs. Potential source rocks include Lower Triassic deep-water clayey limestones and shales as well as Middle Jurassic and Aptian-Albian marine shales. Three oil samples from Triassic and Cretaceous reservoirs form a separate oil family ("Group A"), which is genetically related to oils from the Terek-Caspian fold-and-thrust belt. Group A oils have high C 28 /C 29 sterane ratios and in general contain at least some oleanane. A contribution by Cenozoic source rocks to Group A oils is likely.

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Stratigraphy, Sedimentology and Geochemistry of the Oligocene – Lower Miocene Maikop Group in Dagestan, Ne Caucasus

Cited by 6 publications

References 35 publications

Stratigraphy of the Cenozoic succession in eastern Azerbaijan: Implications for petroleum systems and paleogeography in the Caspian basin

Stratigraphy of the Cenozoic succession in eastern Azerbaijan: Implications for petroleum systems and paleogeography in the Caspian basin

Exploration Plays in the Caucasus Region

Geochemistry of Oils in the Terek‐caspian Foredeep and Prikumsk Swell, Ne Greater Caucasus, Southern Russia

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