TOURNAISIAN CONNECTIVITY

The article presents the results of a comprehensive study confirming the presence of a hydrodynamic connection between the Kizelovsky and Upino-Malevsky carbonate formations of the Tournaisian stage through a system of natural cracks activated by water injection. Based on the analysis of oriented core, noise measurement data, thermometry, and reservoir pressure dynamics, it was proved that fresh water injection into the injection well of the Kizelovsky formation leads to the opening of subvertical cracks that form the channels of fluid migration into the Upino-Malevsky formation. This is confirmed by stabilization of pressure in production wells during injection and its decrease after its shutdown, as well as a decrease in mineralization of the produced water. The results are key to optimizing reservoir pressure maintenance systems and predicting the behavior of fractured carbonate reservoirs.In the modern oil and gas industry, water injection into productive formations remains one of the key methods for increasing oil recovery and reservoir pressure maintenance. However, in fractured carbonate reservoirs, such as Tournaisian deposits, this process involves risks of uncontrolled migration of injected water through natural fractures. This phenomenon is especially relevant for the Upper Tournaisian and Lower Tournaisian substages, where tectonic disturbances and lithological heterogeneity create channels for inter-stratum flows. The consequences of such migration are multifaceted: these are technical problems (flooding of the underlying oil-bearing horizons, decrease in the efficiency of the reservoir pressure maintenance system, corrosion of downhole equipment), and economic losses (increase in water injection costs). The objective of the study is a comprehensive analysis of the conditions, mechanisms and consequences of injected water migration between the Upper Tournaisian and Lower Tournaisian substages, as well as the development of recommendations to minimize the associated risks. To achieve this goal, the following tasks are solved: assessment of the geological and tectonic features of the Tournaisian deposits, including the distribution of natural cracks; identification of key factors affecting the flow (hydrodynamic, geomechanical processes); formulation of practical control measures.This work offers the first comprehensive study of water migration in Tournaisian deposits, taking into account the regional specifics of the Volga-Ural basin. Practical significance. The results of the study can be used to optimize projects for the development of Tournaisian deposits and reduce environmental risks.