Clarification of the genesis of deposits of Qala Suite of the Hovsan-Zykh area by methods of stratigraphic and lithofacies analysis based on 3D seismic and Well Logging data (Absheron oil and gas bearing region, Azerbaijan)

Abstract

The major share of oil, gas and gas condensate produced in Azerbaijan comes from deposits of the Lower Pliocene Productive Series. In this relation, a detailed study of the struc- ture of the Productive Series (PS) deposits and the conditions of their formation is of great practical importance. For this purpose, new, highly data-rich methods of analysis have been widely used in recent years: seismic and sequence stratigraphy. The prediction of non-anticlinal traps and reservoirs in conditions of sharp facies variability of deposits is an urgent problem facing these methods. In recent years, various methods of facies analysis have also been widely used, which allows us to reconstruct the facies conditions and sedimentation conditions of sand bodies and clay de- posits of the PS in the absence or limitation of core material. In this connection, the focus of the work was on studying the conditions of formation of sandy reservoir bodies and clayey screen rocks of fluvial-deltaic and coastal-marine genesis within the Productive Series of the Qala Suite, which is promising from the point of view of oil-bearing capacity, according to both seismic survey and well logging data. The object of the study was the Hovsan-Zykh area, located 20 km east of Baku, in the southern coastal part of the Absheron Peninsula. The industrially significant oil bearing capacity in this area is associated with the deposits of the Qala Suite Productive Series. In order to study the formation conditions of the Qala Suite deposits based on seismic data, paleostructural constructions, as well as seismic stratigraphic and seismic facies analysis of 3D seismic data were performed. Seismic stratigraphic complexes were identified in the section of the study area, and various facies types were defined and analyzed within the Qala Suite strata. Sequence-stratigraphic analysis was performed on the basis of well logging data within the studied formation. In the process of research, the method of logging facies was also applied, which allows lithologic and facies diagnostics of sediments based on well logging data. Taking into consid- eration the new seismic and reinterpreted well data, the deposits in the eastern and western parts of the Hovsan field are divided into individual objects. In the area under study, the deposits of the Qala Suite are represented by alternating interbeds of clayey and sandy rocks and are subdivided into three strata: QaS-1, QaS-2, and QaS-3. Sedimentation conditions for all three units of the Qala Suite are similar, only the paleorelief and the amount of transported material differ, which affected the size and location of the formed traps. According to earlier researches, the boundaries for all deposits in the Qala Suite of the field were determined conditionally due to the lack of more detailed seismic surveys at that time.