Results of the Study of Epigenetic Changes of Famennian–Tournaisian Carbonate Rocks of the Northern Marginal Shear Zone of the Caspian Syneclise (Kazakhstan)

Abstract

Various genetic and morphological types of voids in carbonate reservoirs make it difficult to diagnose them, which can be seen in the determination of reservoir properties in the northern marginal shear zone of the Caspian Syneclise. A macro- and microscopic study of rocks was carried out by staining carbonates in thin sections with alizarin (determination of the mineral composition, structure, texture, void and fracture spaces, rock genesis). Instrumental methods (X-ray, DTA—differential thermal analysis, TGA—thermo-gravimetric analysis, and probe microanalysis) established the composition of rocks, the nature of their diagenetic transformations, and the formation of void space. The elemental and oxide composition of a number of samples was carried out using the X-ray probe microanalysis method, and mineral formations with intermediate thermochemical properties were found. The results of X-ray, DTA, and TGA measurements and the data of probe microanalysis made it possible to reveal thermally inert formations of oxides of calcium, magnesium, silicon, iron, and other compounds in the composition of carbonates. A relatively low-cost express method was used to determine the material composition and the nature of epigenetic changes and to obtain data on the void space as a result of the development of tectonic fracturing and diagenetic processes of leaching and secondary mineral formation in bedded carbonate reservoirs.