A conceptual geothermal deposit model was created based on available geologic, geophysical, and hydrogeologic data. This model assumes that most of the Tbilisi hydrothermal basin is impermeable including the Upper Eocene thereby creating artesian conditions. Another assumption is that there is little or no hydraulic connection between the Tbilisi Central and Lisi districts. Several factors convince us that this is true. For example, hydraulic gradients in the "Lisi" thermal field are much larger than in the Central district suggesting the possibility of lower transmis-sivity. Low values of transmissivity might be caused by greater depths in the "Lisi" aquifer and because lithostatic pressure of upper rocks leads to decrease the size and total volume of permeable fractures. Conversely, decreasing pressure leads to the opening of cracks and thus to an increase in the fracture permeability.
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