South Caucasus Palaeogeography and Prospectivity: Elements of Petroleum Systems From the Black Sea to the Caspian

Abstract

Nine Mesozoic and Cenozoic palaeogeographic maps are presented to illustrate the petroleum prospectivity of the South Caucasus from a fresh perspective and as part of the wider Caucasus region. Previously, elements of petroleum systems – reservoir, source and sealing lithologies, and the timing of their formation – have mostly been examined within individual sub‐basins or licence blocks, and regional understanding has been limited. Emphasis is placed here on the onshore prospectivity of Georgia and Azerbaijan; the well‐known Pliocene Productive Series of eastern Azerbaijan and the southern Caspian is not considered. The Great Caucasus Basin (GCB) formed in the Early Jurassic following closure of PalaeoTethys, and remained a significant feature, despite structural modifications, until end‐Eocene underthrusting and uplift converted the basin into the Greater Caucasus mountains. By the Toarcian a major delta system had developed along its northeastern margin, while the Transcaucasus block to the south was mostly covered by a shallow sea with limited sediment supply. Bajocian volcanism across the South Caucasus was accompanied by modification of the structure of the Great Caucasus Basin with the intrusion of tholeiitic dykes, possibly associated with onset of northward NeoTethyan subduction. Rising sea levels led to the abandonment of the GCB delta system. Relative uplift of the South Caucasus in the Bathonian created lowlands surrounded by marginal settings in which paralic deposits and coals were laid down. Jurassic hydrocarbon source rocks include deep‐marine shales deposited within the Great Caucasus Basin together with coals; their potential is confirmed by numerous seeps within both Georgia and Azerbaijan. Various Middle Jurassic sandstones are potential reservoirs. Carbonates dominated by the late Callovian, with widespread development of Oxfordian reefs and of Late Jurassic evaporite basins in the North Caucasus. Bedded anhydrites in Georgia comprise potential seals. Shallow‐marine clastics again became widespread across the Caucasus in the Cretaceous, later replaced by carbonates including chalk‐like limestones. Deeper‐marine conditions persisted in the Great Caucasus Basin, which became less well‐defined and split into separate depocentres. Fractured chalks are known reservoirs in the North Caucasus and prospective reservoirs in the South Caucasus. Uplift of the southern South Caucasus during the Paleogene led to northward transport of sediment into evolving E‐W to ESE‐WSW basins in eastern Georgia and western Azerbaijan. Marine deposits within these basins form reservoirs, including thick fractured volcanogenic turbidites in eastern Georgia. Reduced sediment supply here at the start of the Late Eocene allowed organic‐rich restricted‐marine source rocks to accumulate. Rapid uplift of the GCB associated with underthrusting at the end of the Eocene led to emergence of the Greater Caucasus mountains. The prolific Maikopian source rocks were deposited in restricted‐marine conditions during the Oligocene and Ear...

Reservoir Characterization of the Pliocene Red Series, Lam Field and Surrounding Areas, Offshore Western Turkmenistan

“…This is widely assumed also to be the case in the eastern, Turkmenistan, sector of the basin (Torres, 2007), but there is no direct evidence for this owing to the absence of pre-Pliocene outcrops or relevant well penetrations of the equivalent horizons here. Although Iranian outcrops in the SE of the Basin indicate the absence of significant Cenozoic source rocks in this area (Zeinalzadeh et al, 2021), regional palaeogeographic mapping indicates that potential Maikopian source rocks are more likely to have developed in the NE of the basin, in the offshore Turkmenistan sector (Blackbourn Geoconsulting, 2001;Blackbourn et al, 2021), and we regard the Maikop Group as the most probable major source of hydrocarbons within LAM and adjacent fields.…”

“…The South Caspian Basin is thought to have been formed originally as a back-arc basin lying to the north of the northern margin of NeoTethys during the Middle Jurassic (Blackbourn et al, 2021). It now accommodates over 20 km of sediments, a substantial proportion of which (perhaps up to 7 km) has accumulated since the beginning of the Pliocene owing to a period of rapid subsidence associated with compressional underthrusting of the South Caspian crust beneath the Apsheron-Prebalkhan uplift zone.…”

“…2 shows a general stratigraphic column for the eastern South Caspian Basin and Western Turkmenistan (Torres, 2007). The Oligocene to middle Miocene Maikop Group along with the upper Miocene Diatom Formation are considered to be the key source rocks in this region, and are responsible for charging reservoirs at fields both in the South Caspian and in the wider Greater Caucasus area (Goodwin et al, 2020;Blackbourn et al, 2021;Tari et al, 2021;Sachsenhofer et al, 2018a). Both structural and stratigraphic traps at these fields are widespread (Tari et al, 2021).…”

An Interpretation of Crustal Structure and Hydrocarbon Evolution of the South Caspian and Kura Basins, Azerbaijan

“…A vast multiplicity of sources contributed to the synthesis of isopach maps which allowed the construction of the rst regional geologic model that incorporates key bounding surfaces and stratigraphic units (Abdullayev et al, 2017;Abreu and Nummedal, 2007;Blackbourn et al, 2021;Bochud, 2011;Glumov et al, 2004;Green et al, 2009;Guliyev et al, 2001). Temperature data was obtained from over 150 onshore and offshore wells, with depths ranging from 100 to 6000 m (Alizadeh et al, 2017;Mukhtarov, 2004;Mukhtarov, 2018).…”

“…GCFTB forms a barrier along the southern margin of the Scythian Platform from the Eastern Black Sea to SCB (Bochud, 2010). GCFTB is an inverted relict of the deep-water Greater Caucasus Basin (GCB), formed as an elongated WNW-ESE trending rift basin located along the early Cimmerian suture, sub-parallel to the Neo-Tethyan ocean margin (Blackbourn et al, 2021;Tari et al, 2021). Kura Basin is divided into three subordinate sub-basins: 1) the Upper Kura basin or Kura-Qabirri inter uve; 2) the Middle (Central) Kura basin, mostly occupied by the Yevlakh-Agcabedi Depression (YAD); and 3) the Lower Kura basin separated from the Middle Kura by the volcanic Kurdamir-Saatli uplift and the West Caspian fault (Fig.…”