OIL AND GAS PROSPECTS OF THE SHAMAKHY-GOBUSTAN DEPRESSION IN RELATION TO ITS STRUCTURAL AND TECTONIC PROPERTIES

• Main Authors: Gultar Jumshud kizi Nasibova, Khuraman Z. Mukhtarova
• Format: Article
• Language: Russian
• Published: Tomsk Polytechnic University 2021-04-01
• Series: Известия Томского политехнического университета: Инжиниринг георесурсов
• Subjects: thickness; sand content; prospects; zone; structure; sediments; amplitude; age; cover; tectonic fault; overthrust; cleavage; oil; gas
• Online Access: http://izvestiya.tpu.ru/archive/article/view/3143/2440

For quality assessment of intensity of the area distribution of compressional stresses (geodynamic factor in the Shamakhy-Gobustan depression) and to study its impact upon folding, faulting and mud volcanism, the authors have studied the morphological properties of locally developed uplifts and mud volcanoes, and based on the results obtained have built the maps showing the properties of the magnitude variation of the amplitudes of the faults complicating the structures as well as isomorphic maps reflecting area distribution of compressional stress within the stratigraphic units of the Cretaceous for the northern, Maikopian – for the central and Productive Series – for the southern zones. The studies have revealed that the cones of mud volcanoes, common in the northern zone, where intense compressional stresses are manifested, are relatively smaller than the cones of mud volcanoes of the central zone, and those of the southern zone are larger, that is, the cone dimensions increase from north to south in the direction of decreasing intensity of compressional stresses. It should be noted that this can also be associated with a favorable change in the lithofacies composition of the section in the same direction, which is one of the main factors in the formation of mud volcanoes. In order to determine the role of the lithofacies factor in the formation of both mud volcanoes and faults of various types within the study area, based on the composite lithostratigraphic section the authors drawn the diagram, reflecting the clay and carbonate content in the corresponding stratigraphic time intervals. At the same time the maps reflecting natural oil and gas shows and well data for the zones of the Shamakhy-Gobustan depression under study, where natural oil and gas shows of various types and origin are widespread, were made and based on the studies carried out for each zone, association of oil and gas shows with folding and faulting as well as that of the physical and mechanical properties of rock complexes with geodynamic processes were established. Relevance. The Shamakhy-Gobustan depression, located in the southeastern part of the Greater Caucasus megaanticlinorium, is distinguished by a complex tectonic structure. According to its geomorphological, tectonic, lithological and stratigraphic properties, as well as oil and gas content, the depression is divided into northern, central, southwestern, southeastern Gobustan and Alat tectonic zones. Local uplifts developed within these zones are complicated by high-amplitude overthrusts and tectonic nappes. The study of the impact of compressional stresses (geodynamic factor) upon folding and faulting, mud volcanism and oil and gas content for the zones of the area under investigation stands out for its relevance. Decrease in intensity of compressional stresses from north to south along with increasing prospects of oil and gas content of the area is observed within the depression. The reason, as a rule, is the migration of fluids from high pressure zones towards low pressure zones. At the same time, along with the geodynamic factor, the reasons for the high prospects of the southern zone of the study area are the increase in the thickness of the Maikop, Chokrak and Productive Series (N21b) sediments southwards and the spread of horizons of sandy reservoirs of sufficiently high thickness in the lithological composition. The main aim of the study is to investigate the areal distribution properties of the main geodynamic factor – compressional stresses, which play an important role in formation and evolution of local uplifts and faults of various types complicating them, also of mud volcanoes, and in distribution of oil and gas fields within Shamakhy-Gobustan depression. Subjects: structures and their lithofacial composition formed by Mesozoic deposits in the northern, Paleogene-Miocene deposits in the central and Pliocene deposits in the southern zones of the Shamakhy-Gobustan depression. Methods. Using the morphology variation properties of folds developed in the Shamakhy-Gobustan depression, maps reflecting the magnitudes of the fault amplitudes along with isomorphic maps for the surfaces of Cretaceous, Maikop and Pliocene, northern, central and southern zones, as well as a diagram of the prospects for the oil and gas content of the area were built, intensity of distribution of compressional stresses in each zone were assessed. Results. Compressional stress, as a geodynamic factor, played a significant role in formation of structural and tectonic layout of the sedimentary cover of the Shamakhy-Gobustan synclinorium. Local uplifts developed in all three zones of the Shamakhy-Gobustan depression were formed under the impact of both longitudinal and transverse bending mechanisms; widely developed mud volcanism, which is an indicator of oil and gas content, within the Shamakhy-Gobustan synclinorium and numerous natural oil and gas seeps make it possible to highly assess the prospects for oil and gas potential of autochthonous limbs of thrust and cover type structures; due to the direct impact of the distribution properties of the compressional stresses on fluid migration and formation of accumulations, depending on the geodynamic regime in the sedimentary cover, there is decrease in intensity of compressional stresses and increase in the oil and gas content of the area from north to south.