One of the most effective thermal methods for oil recovery enhancement in case of high-viscosity oil reservoirs is the technology of steam cyclic stimulation of the well. Using this method, RITEK LLC was able to put into development previously unprofitable high-viscosity oil reservoir in the Volga-Ural oil and gas bearing region. However, sequential laboratory studies of physico-chemical processes occurring in carbonate rock during steam cyclic treatment of the reservoir at temperatures of 250-350°C allowed to identify processes that affect the reduction of rock permeability, which leads to a decrease in the treatment efficiency. In the course of determining the relative phase permeability in the stationary mode during the filtration of oil and water, a significant irreversible decrease in the permeability of the core model was noted. Extended studies of samples of rock-reservoirs of high-viscosity oils allowed to identify a series of sequential, interrelated processes that underlie the reduction of permeability. Such a process is partial or complete destruction of the microcrystalline calcite rim with subsequent colmatation, local formation of organic hydrophobic films in the pore space, as well as the formation of needle-like technology-induced crystals at high temperatures. This study is devoted to the study of newly formed minerals as a result of high-temperature filtration experiments on the core model and hydrothermal impact on the rock crumb in reservoir conditions. The study of the rock was carried out by a number of lithological-mineralogical methods: petrographic study of thin sections, X-ray phase analysis, scanning electron microscopy, transmission electron microscopy with electron diffraction, micro-X-ray spectral analysis. According to the results of the study, it was found that during the hydrothermal impact on carbonate rocks in the presence of quartz, minerals of the group of calcium hydrosilicates (tobermorite, xonotlite, etc.) are formed, which fill the void space and significantly reduce the pore space and filtration ability of the rock, which worsens the filtration of fluids in the reservoir. The obtained results will allow to reasonably approach the development of ways to prevent the filling of the void space with newly formed crystals during the steam cyclic stimulation, which will lead to an increase in oil recovery.
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