Influence of Structural and Tectonic Factors on the Hydrogeochemical Zonation of the Lower-Middle Cambrian Litvintsevskaya Suite Aquifer

Abstract

Groundwaters of the Lower–Middle Cambrian Litvintsevskaya suite aquifer within the study area, located in the northeastern part of the Upper Lena artesian basin, are used for water supply in reservoir pressure maintenance systems during oil field development. The relevance of the study is driven by the need to understand the significant factors controlling the formation of their chemical composition. The aim of the study is to determine the nature of the influence of the structural and tectonic factor on the hydrogeochemical zonation of the object. Research methods: data preparation, classification and clustering, statistical characterization of groundwater chemical composition parameters, calculation of major ratios, and thermodynamic modeling of groundwater equilibrium with the main rock-forming minerals. Results. For the first time for the object under study within the investigated area, the following results were obtained. In the Western tectonic block, weak brines of chloride-sodium composition are distributed, while in the Central and Eastern blocks, fresh and slightly brackish waters of the hydrocarbonate and sulfate class, calcium group, occur. The mineralization of groundwater increases with depth and in the direction of flow; in fault zones, it mixes with deep brines. In the Central and Eastern areas, the main hydrogeochemical processes are the weathering of carbonate and silicate rocks; in the Western area, dissolution of rock salt or influx of deep waters dominates. The groundwaters of the object are supersaturated with calcium; in the Western block, they are close to equilibrium with respect to gypsum and anhydrite. The significant difference observed in the level of mineralization and the ionic‑salt composition of groundwater suggests a separate evolution of groundwater on either side of the western fault. The chemical composition of the waters directly depends on their interaction with the rocks, the structural-tectonic factor has a significant influence, which determines the formation of the hydrogeochemical zonality of the object. The established patterns serve as a basis for predicting groundwater quality. A promising direction is further research into the hydrogeochemical processes occurring during groundwater formation and assessment of their impact on the technological parameters of oil field development.