Physical, chemical and biological processes controlling groundwater flow in geothermal reservoirs

Maren Brehme1, Guido Blöcher1, Simona Regenspurg1, Peter Leary2, Fatih Bulut3, Harald Milsch1, Axel Sanden4, Floris Veeger4, Siklosi Istvan5, Robertas Valickas6, Sigitas Petrauskas6
1 Geothermische Energie Systeme, GFZ Potsdam
2 Institute of Earth Science and Engineering, The University of Auckland, New Zealand
3 Kandilli Observatory and Earthquake Research Institute, Geodesy Department, Bogazici University, Istanbul, Turkey
4 VEEGEO Geothermal Energy, 3032 AL Rotterdam, Netherlands
5 Mezőberény Város polgármestere, Mezőberény, 5650 Hungary
6 UAB GEOTERMA, LT-94100 Klaipėda, Lithuania

P 3.6 in Deep geothermal energy and deep groundwater

Characterization of groundwater flow in geological media is essential to sustainably develop geothermal reservoirs. Groundwater flow in geological media occurs on grain scale in spatially correlated physical structures where few high permeable structures control the main flow volume. When these high permeable structures are clogged by small particles, fluid flow decreases very fast leading to negative commercial implications for the site. Clogging processes are often related to field operations or artificially intruded materials and can be of physical, chemical or biological nature. However, which processes are triggered by field operations, how the different processes interact and the subsequent implications on the reservoir are still insufficiently understood.

However, basic analysis of fluids and solids sampled at the site already explain fundamental controls on fluid flow in the reservoir. In this study we investigate a wide range of field data from different geothermal fields in Europe. The geothermal power plants are in different phases of operation, from drilling to operation.

Water, gas, core and filter residual samples have been analyzed with various methods and compared to historical data from each site. Results give information on rock structure, hydraulic properties, chemical composition and biological activity in rocks and fluids. Chemical processes observed are e.g. mineral precipitation and corrosion. Microbial activity causes biofilm while fines migration is caused by changes in physical conditions of the reservoir. Moreover, different processes can affect each other and trigger further reactions. At one site e.g. microbial activity triggers corrosion in surface pipelines.

We conclude that field data already allow to elaborate on subsurface processes. Especially the interaction of physical, chemical and biological processes is important to consider. Reasons for injectivity decline should be understood at an early stage to avoid long-term reservoir degradation.