IMPACT OF AQUIFER HEAT STORAGE ON HYDRAULIC PERMEABILITY - RESULTS FROM A COLUMN EXPERIMENT

Aquifer Thermal Energy Storage (ATES) is a sustainable alternative for storage and seasonal availability of thermal energy (heating or cooling). Its impact on the aquifer, however, is not well known. In Berlin (Germany), the Jurassic (Hettang) sandstone aquifer with highly mineralized groundwater (TDS 27 g/L) is already used for heat storage. The aim of this study was to examine the hydrogeochemical changes that result from the temperature enhancement and its effects on the hydraulic permeability of the aquifer.

A column experiment was conducted, in which a stainless steel column was filled with unconsolidated sediment from the aquifer and was flushed with original groundwater for more than two months. The initial temperature of the experiment was 23°C, comparable to the in-situ conditions within the aquifer. After reaching equilibrium between sediment and water, the temperature was increased to 37° to simulate heating up of the aquifer. During the experiment, physical and chemical parameters (pH, ORP, dissolved oxygen and dissolved carbon dioxide) were measured at the outflow of the column and the effluent water was sampled regularly. Changes in hydraulic properties of the sediment were studied using two tracer tests with Uranin, which were conducted right before the increase of temperature and at the end of the experiment. The observed alterations were verified using a Scanning Electron Microscope for the deposition of precipitated minerals and biofilms on sediment grains.