Thermohydrodynamic modeling of the influence of deep faults and degassing channels on groundwater dynamics

Abstract

The authors developed a thermohydrodynamical 2D model of a vertical section of the geological environment of groundwater, taking into account deep active geodynamic zones. Such zones (fast filtration and migration zones — FFMZ) are actually permeable faults and their associated surface depressions and under-depression degassing channels. Their depth may be different, but they are also very deep (more than 7 km). Under these conditions, the formulation of a purely hydrodynamic problem is insufficient. It is necessary to take into account the heat flux coming from the interior and affecting the hydrodynamic features of the filtration. The HYDROTHERM program used by the authors, developed by the US Geological Survey, allows us to solve such problems. The hydrogeological schematization of the model section is selected in accordance with its intended location within the left bank of the Kyiv region, the Dnieper―Trubizh interfluve. To build the model, the authors used the available data on the location, distribution density over the territory, and the characteristics of the FFMZ activity. The vertical distributions of temperature and fluid flow rates are obtained, and the deep influence of the FFMZ on their formation is clarified. The presence of a dilatency zone, which is characterized by branching of fractures in the geological environment, is confirmed at a depth of 3―7 km at specified parameters of the model. In this zone, with a decrease in depth, an intermittent process of discharge of a stress-strain state of rocks, a decrease in the pressure of the ascending fluids, and their gradual degassing occur. The activation of fluid flows at these depths without preliminary specifying increased permeability in the model indicates the participation of fluids in the formation of the dilatancy zone.