Thin-dispersed mineral phases of bitumen-saturated deposits of Tatarstan (Russian federation) under electronic microscopy and energy-dispersive X-ray spectroscopy data

Abstract

© SGEM2019. Bituminous sandy rocks occur in the area between the river Volga and Ural mountains (Republic of Tatarstan, Russia) in the sediments of the Permian age. According to the mineral composition, they belong to the graywacks and are composed of quartz grains, feldspars, effusive fragments, etc. The study of their composition and structure was carried out in order to identify the factors of localization of oil and bituminous substances. However, mineral particles of pelitic and smaller dimensions remained practically unexplored. Studies carried out using a scanning electron microscope with energy-dispersive spectroscopy, allowed to study in detail the finely dispersed component of tar sands and sandstones. It is established that ultra-disperse mineral phases are characterized by a large variety of composition and genesis, which is caused by sedimentological, post-sedimentological factors and by the influence of hydrocarbons penetrating from the lower horizons of the earth's crust. According to the conditions of formation, ultra-dispersed mineral phases are confidently divided into groups of allochthonous and autochthonous. Allochthonous mineral particles are rock-forming minerals: Quartz, feldspars, etc. They can also be divided into two groups, represented by the products of destruction of the parent rock complexes and the newly formed ones, which arose during hypergenic destruction and transfer. The autochthonous group of ultra-dispersed mineral phases is represented by minerals formed in the formation of rocks in the process of diagenesis as a result of deposition on geochemical barriers arising within the reservoir system. The evolution of the sedimentary sequence is restored by ultrafine mineral phases, and the stages of its formation are revealed. The paper discusses the causes and forms of the appearance of various minerals in the studied sandy sediments. One of the unexpected findings was palladium with a content of up to 1% in point analysis. Its source can be destructed basic-ultrabasic rock complexes of the ancient Ural mountains. From the weathering zones, it was transferred in the form of soluble in water metal-organic complexes and accumulated in natural waters by sorption of sediment with clay minerals and organic matter under reducing conditions. This is evidenced by the genetic relationship of palladium with framboidal pyrite, illite and montmorillonite. Despite their small size, ultra-dispersed mineral particles can have a significant impact on the field development process, precipitating and blocking the migration routes of hydrocarbon fluids, as well as creating technogenic accumulations in production pipes.