Characterization of the hydraulic properties of a planned Aquifer Thermal Energy Storage (ATES) system during well development

For all applications dealing with the production or injection of groundwater, it is extremely important to know the hydraulic characteristics of the aquifer for a proper site planning and successful project development. The hydraulic tests required for this are usually carried out after drilling and setting the filter and include a first well development in order to minimize the influence of the drilling mud and the alteration of the near wellbore area caused by the drilling operation. This normally requires a temporal decoupling of the first well development and the main hydraulic test to be carried out afterwards. In order to optimize the ATES development, a combination of well development and hydraulic testing including physicochemical monitoring is suggested. This method was carried out at the High-Temperature Aquifer Thermal Energy Storage (HT-ATES) site in Berlin Adlershof to show that hydraulic parameters, such as productivity index, skin factor, transmissibility, and storage coefficient can also be determined already during the well development. For this purpose, five- and two-stage step-rate tests were carried out, each with subsequent shut-in phases. The combination of analytical and numerical modelling was employed to analyse the test performance. For the analysis, radially varying permeability around the borehole was assumed in order to identify the influence area of the drilling mud and to determine its transient course. The application of a combination of a classic transient pressure analysis together with numerical models leads to a reliable characterization of the aquifer. For the Hettangian (Jurassic) aquifer, which was accessed via a filter section between 369 and 387 m TVD, this combination of methods, indicates a permeability of 1.5 to 2.0 D and a productivity index of 1.1 to 1.2 l/s/bar. The method enabled to determine the drilling mud influence area which is in the range of 0.35 m and corresponds to, a skin factor of 0.7 to 1.8.