Abstract
The features of the oil-bearing capacity of the productive strata of Permian deposits in the interval of 117.5-188.6 m along the section of individual wells of the Ashal’cha field of heavy superviscous oil (Tatarstan) were revealed depending on the content, composition, and thermal effects of organic matter (OM) oxidation in the rocks. It is shown that the rocks are very heterogeneous in their mineral composition and in the content of both free hydrocarbons by extraction with organic solvents and insoluble OM closely associated with the rock. The total content of OM in rocks varies from 1.72 to 9.12%. The features of group and hydrocarbon composition of extracts from rocks are revealed depending on their mineral composition and the content of organic matter in them. According to the molecular mass distribution of alkanes of normal and isoprenoid structure, extracts from rocks are differentiated according to three chemical types of oil: type A1, in which n-alkanes of composition C14 and above are present, and types A2 and B2, in which n-alkanes are destroyed to varying degrees by processes microbial destruction, which indicates a different intensity of biochemical processes in productive strata of Permian sediments. These processes lead to a decrease in the amount of OM in the rocks and an increase in the content of resins and asphaltenes in the oil extracted from them, as well as an increase in the viscosity of the oil. Using the method of differential scanning calorimetry of high pressure, it was found that the studied rock samples differ from each other in quantitative characteristics of exothermic effects in both low-temperature (LTO) 200-350°С and high-temperature (HTO) 350-600°С zones of OM oxidation. The total thermal effect of destruction processes of OM depends on the content of OM in the rocks and its composition. The research results show that when heavy oil is extracted using thermal technologies, the Permian productive strata with both low and high OM contents will be involved in the development, and the general thermal effect of the oxidation of which will contribute to increased oil recovery.
Highlights
The huge amount of heavy oil and natural bitumen resources are concentrated in the territory of Tatarstan, in deposits of Permian system [1,2,3,4,5,6,7,8,9,10]
The sandstones of the Sheshmin horizon form traps that can be combined into specific zones with certain conditions of their formation, development history and structural features, which determined the conditions of occurrence, the placement, and the distribution ratio of formation fluids—heavy oils, bitumens, and formation waters
In the context of modern methods of converting heavy oils and natural bitumens directly into the oil-bearing rocks, a comprehensive study was conducted of the material composition of oil and bitumen-containing rocks selected from the depth interval of 117.5–188.6 m in the individual wells of the Permian deposits of the Ashal’cha field
Summary
The huge amount of heavy oil and natural bitumen resources are concentrated in the territory of Tatarstan, in deposits of Permian system [1,2,3,4,5,6,7,8,9,10]. Most of the explored deposits of heavy oil and natural bitumen in Tatarstan are concentrated in the Kazan and Ufa deposits of the Permian system and are associated with the main part and the western slope of the South Tatar Arch (STA) and the eastern side of the Melekess Depression [4,5,6, 9, 11]. An analysis of the occurrence conditions of the deposits of the sandy bundle of the Sheshmin horizon shows their complex and heterogeneous structure within the Permian deposits of the structural zone of the western STA slope [9, 15]. Studies of many authors [1, 2] showed that the conditions of occurrence of heavy highviscosity oil and natural bitumen deposits in Tatarstan largely determine their composition and nature of saturation of the rock with bitumen, and depend on the choice of areas of exploration and methods for their development
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