Azerbaijan - Geology.
- The onshore Lower Kura, Shamakhy-Gobustan and Absheron areas, and the offshore archipelagos of Baku and Absheron. Their thick sandstone formations (Fms) of the Middle Pliocene - known as Productive Series (PS) - are the main reservoirs. They have produced since the late 19th century.
- The Middle Kura depression between the Greater and Lesser Caucasus mountain ranges. Their main oil reservoirs are in the PS. There are poor reservoir properties in some of the Upper Cretaceous volcano-genic rocks and the Paleogene, Miocene and Upper Pliocene Fms. There are fairly large oil and gas reservoirs in the Yevlakh-Aghjabedi trough; oil pools developed in a wide stratigraphic range - such as the Akchagylian, Sarmatian, Chokrakian, Maikopian, Eocenian and Upper Cretaceous Fms.
- The Pre-Caspian Guba region, north of Azerbaijan. Hydrocarbons there are associated with Jurassic, Cretaceous, Paleogene, Miocene and Pliocene sediments.
Also important to note, Azerbaijan is in the first place in the world for the amount of mud volcanoes - one of the visible signs of the presence of oil and gas reserves hidden deep beneath land and sea in the Caspian region. Gas seeps occur when a pocket filled largely with methane gas under the ground finds a passage to the surface. One such famous gas seep is Yanar Dagh (fire mountain) on the Absheron Peninsula where a continuous fire burns along a hill-side. People often go there to see dancing flames which never get extinguished. It is easy to understand how such eternal fires became objects of worship. The appearance of the Zoroastrians in Azerbaijan almost 2,000 years ago is closely connected with these geological phenomena. The name Azerbaijan was derived from the word "fire" in Persian. Fire worship was paramount throughout pre-Islamic history in this region.
Important resources other than petroleum are contained in what mud volcanoes bring out of the earth. There are in the Caspian region about 350 of the world's 800 volcanoes, of which 140 are sub-marine. Eight islands in the Baku Archipelago are mud volcanoes by origin. Mud volcanoes first began their activity in Azerbaijan 25m years ago (see Azerbaijan's mud volcanoes & their resources in Google).
The Middle Jurassic's thickness in Azerbaijan is up to 4,300 metres. Mid-Jurassic deposits are distributed widely in the water-shed section of the Major Caucasian Ridge and in its frame. These are represented by black slates inter-bedded with sandstones and aleurolites. Deposits occur within the Tengi-Beshbarmag anti-clinorium and the super-imposed trough of Gusar-Devechi.
There are deposits from Lusitanian, Kimmeridgian and Tithonian stages in the water-shed section in Tengi's lateral ridge, composed of carbonaceous and sandy-argillaceous rocks and are represented by two lithofacies.
Upper Jurassic carbonaceous litho-facies, mainly of the Tithonian stage, predominate in the Shahdag region. They were traced from the massifs of Shahdag and Gyzulgaya up to the Tengi gorge. They consist of dense and highly fractured limestones and dolomites which are zoogenic and pink. There are abundant sandy-argillaceous litho-facies in the central and south-eastern Caucasus and within the lateral ridge. They consist of clayey slates, alternated with aleurolites, sandstones, marls and partially limestones. The litho-facies subside towards the Shamakhy-Gobustan region.
Lower Cretaceous deposits are trans-gressively over-lain by those of the Upper Jurassic. Upper Jurassic's thickness in these areas is up to 1,500 metres. Cretaceous deposits are spread widely in the Greater Caucasus mountains.
Jurassic sediments are post-mature for oil and gas. Generation may have been late enough to enable migration and accumulation into shallower reservoirs. Hydrocarbons remaining in situ may have been displaced by gas generated at high temperature.