Factors and mechanisms of productive secondary reservoirs formation in deep-lying oil and gas complexes. Article 2. Carbonate minerals – lithogenetic and tectonophysical indicators of the secondary reservoirs conditions formation at large depths

Abstract

Authigenic carbonate minerals, together with clayey matter, play a leading role in the cementation of terrigenous phaneromorphic (granular) rocks. Studying the regularities of carbonate authigenesis is of primary importance for oil and gas geology. Due to a sharp change in the tectonic regime (neotectonic stage of the development of the oil and gas basin), dislocation epigenesis is regionally superimposed on the catagenetic zonation (the leading role of load pressure and increase in conductive heating temperatures). Like catagenesis, it has a regional character, but its intensity, both in section and laterally, varies widely, determined primarily by shear tectonics. The most striking indicator of this radical change is the replacement of ankerite with siderite. The most important feature of siderite is the presence of varying degrees of pronounced hatching, which is characteristic of shear plastic (micro)deformations. This, on the one hand, allows to consider late epigenetic siderite as a tectonophysical indicator, and on the other hand, it indicates a radical change in the tectonic regime, thanks to which catagenesis is replaced by dislocation epigenesis. This allows to draw conclusions that are extremely important for elucidating the mechanisms of formation of oil and gas deposits in general and in deep-seated complexes in particular. So, summarizing the results of research on carbonate minerals of deep-seated secondary reservoirs, we have grounds for defining a fundamentally new stage in their use as indicators of certain stages of epigenesis. At one time, researchers were able to determine a number of chemical-mineralogical and structural parameters of calcite and other carbonates, which made it possible to use carbonate cements as indicators of diagenesis – initial epigenesis (protocatagenesis) and deep epigenesis (meso-apocatagenesis). Now they can be used not only as indicators of various stages of epigenesis, including dislocation epigenesis and hypogenic allogenesis, but also as indicators of tectonophysical factors in the formation of productive secondary reservoirs, in particular, those formed at the neotectonic stage of NGB formation.

Keywords

• carbonate minerals
• secondary reservoirs
• deep-lying complexes
• electron microscopic scanning