Substantiating of oil and gas prospects of Mesozoic sediments based on the geochemical model of mud volcanoes in the Shamakhi-Gobustan structural element of the South Caspian megadepression
Authors: Zeynalova Sevil A. , Manyuk Volodymyr V. , Karimzade Firdus R. , Shahbazov Rufat A. , Zahidova Tamella E. 
Published: September 2024

There are up to 120 mud volcanoes in the Shamakhi-Gobustan region. During the process of mud volcano eruptions, a large amount of solid, liquid, and gaseous products are thrown to the Earth’s surface, which are widely used for the identification of oil and gas deposits and are considered the main indicator of the productivity of the basin. According to laboratory results from the analysis of solid, liquid, and gas products of mud volcanoes, it is possible to obtain detailed information about the oil-gas content of deep-lying sediments. Therefore, the study of the geochemical composition of the mud volcanoes in the Shamakhi-Gobustan trough plays a major role in the discovery of new oil-gas and gas-condensate deposits. To clarify the changes in the chemical and isotopic composition of gases from mud volcanoes in the Shamakhi-Gobustan trough and to evaluate the oil-bearing and gas-bearing potential of Mesozoic sediments, the characteristics of changes in the isotopic composition of methane gas, heavy hydrocarbons, carbon dioxide, ni- trogen, as well as CH4 and CO2, were studied. The amount of methane in the gas emissions released from mud volcanoes in the Azerbaijan region is more than 90%. The amount of CH4 in the mud volcanoes of the Shamakhi-Gobustan trough ranges from 78.5% to 97.56%. The minimum amount of methane is found in North Gobustan (Gizmeydan 86.8%, Malikchobanli 78.5%), while relatively high amounts are mainly noted in Central (Kushchu 97.55%) and South Gobustan (including Dashgil 97.57%, Goturdag 96.55%, Bahar 96.78%). Mud vol- canoes are less developed in the North Gobustan region and are small in size. In the Central zone, both the size and the number of volcanic cones increase significantly compared to North Gobustan. The largest and most active volcanoes have developed in the southern zone of the trough. Huge mud volcanoes such as Dashmerdan, Solakhay, Ayrantoken, Goturdag, Kirdag, and other volcanoes have developed along the Alat range. The mud volcanoes of North and Central Gobustan are mainly confined to Cretaceous and Paleogene sediments, and due to the low occurrence of plastic clay rocks in these sediment sections, mud volcanoes are rare and weakly active. On the contrary, to the south of these zones, that is, in South Gobustan, they are located in Pliocene sediments, and due to the presence of very thick plastic rocks in their section, mud volcanoes are widespread, and they are active volcanoes that are morphologically sharply reflected. It should be noted that in areas where plastic clay rocks with significant thickness and rheologically active properties are developed, large cones of mud volcanoes that erupt frequently are observed. The calculated gas production of mud volcanoes increases from the northern zone towards South Gobustan. Thus, while the calculated gas production of the Nabur volcano located in the Northern zone is 1500 m3/day, the calculated gas production of the Dashgil mud volcano located in South-Eastern Gobustan is 40,000 m3/day. In the central and south- ern zones of the Shamakhi-Gobustan trough, the presence of ancient rock fragments from the Oligocene-Miocene (Maykop) age rocks forming their roots in the solid waste of mud volcanoes (Cretaceous, Paleocene, Eocene), a large percentage of methane gas (97.57%), transverse elevations, and the presence of an intersection zone of longitudinal faults suggests that there is a tectonic rupture zone rich in natural gas below the base of the volcano. This is proven once again by the occurrence of gas flows in Anart (110,000 m3/day), Utalgi (50,000 m3/day), and the Touragay field (20,000 m3/day). The presence of oil films in the eruption products of mud volcanoes indicates the accumulation of oil alongside gas.