Modelling of geochemical properties of mud volcano eruption products and relationship with oil and gas prospects within the South Caspian megadepression of Lower Kura region

Abstract

During the activity of mud volcanoes, a large amount of solid, liquid and gaseous products are thrown to the surface of the earth, which are widely used in the prospecting for oil and gas deposits, as well as being considered as the main indicator of the productivity of the basin and oil and gas generation. According to the laboratory results of solid, liquid and gas products of mud volcanoes, detailed information can be obtained about the lithological composition of rocks, conditions of sedi- ment accumulation, and oil and gas saturation of sediments at a depth that is impossible to study with wells. The main oil-gas complex involved in the geological structure of the deposits of the Lower Kura depression is the Productive Series (PS) sediments. The eruptive apparatus of all volcanoes cuts through the Productive Series, and oil and gas deposits are also found within this layer. The amount and age of gas emissions of mud volcanoes is one of the main factors in assessment of oil and gas potential and gas generation zones of Earth’s interior. In this regard, solving the problem of oil and gas content of deep-lying sediments is closely related to the study of mud volcano gases. The results of numerous analyses show that the chemical composition of the gases of the mud volcanoes of Azerbaijan is the same. In this regard, the study of the geochemical composition of the mud volcanoes of the Lower Kura depression plays a major role in the discovery of new oil-gas and gas-condensate deposits. In addition, luminescent-bituminological and gas-geochemical studies have been conducted and 32 samples analysed taken from mud volcanoes that complicate the local folds of the Lower Kura depression. Using the results of the analysis, the change in the chemical composition of the gases of mud volcanoes in the Lower Kura depression was clarified, and in order to evaluate the prospect of oil-gas-bearing of the deep-lying sediments, the composition of methane gas, heavy hydrocarbons, carbon dioxide, nitrogen were determined, and the isotopic characteristics CH4 and CO2 were investigated. Based on these analyses, the amount of methane gas in the Lower Kura depression ranges from 78.6 to 99.13%. The presence of rheologically active clays of Oligocene-Miocene (Maykop) age, ancient Cretaceous rock fragments, which form its root in the solid wastes of the mud volcanoes of the Lower Kura depression, a large percentage of CH4 (98%), according to geochemical analysis, and the intersection zone of the latitudinal and longitudinal faults within the tectonic structure of the uplifts allow us to assume that there is a tectonic friction zone with natural gas under the base of the volcano. This is proven once again by the presence of gas flows (600,000 m3/day) in the Babazanan-Durovdag area. The fact that a large amount of gas is released in mud volcanoes proves that there are porous reservoirs in the deep layers of the area, where rich gas deposits are located. The presence of oil films in the eruption products of some volcanoes indicates the accumulation of oil simultaneously with gas.