The assessing of the quality of geothermal reservoirs on the example of the Lower Triassic aquifer in the Mogilno-Łódz Trough (Polish Lowlands)

Abstract

Petrographic and petrophysical investigations of the aquifers allow to estimate their productivity and infectivity, as well as allow for better recognition of the origin of the chemical composition of geothermal waters. Deep deposition of the Lower Triassic sediments in the analysed area (locally above 5000 m b.s.l.) is conducive to high temperatures (above 90°C) within the reservoir and causes deterioration of reservoir parameters. The Lower Triassic geothermal reservoir consists of fine and mixed grain-size sands and sandstones layers from 10 to 650 m thick; depending on the depth. The water within the reservoir exhibits mineralization ranging from 2 to over 100 g L-1 and its temperature ranges from 30 to 100°C. The mineralization of waters varies from 140 g/dm3 (Warsaw basin) to over 350 g/dm3 in the deep zones of the basin (axial fragments of the Mogileńsko-Łódz trough). The average permeability of reservoir layers in the Polish Lowlands is 145.5 mD.