An Integrated Modelling Study of Hellisheidi Geothermal Reservoir

Abstract

Performance of geothermal reservoirs can be controlled by the hydrodynamic, thermal, mechanical, and chemical interactions taking place during heat extraction. Fracture network characterisation can affect the life span of geothermal reservoirs and operational constraints. In SW-Iceland Hellisheidi geothermal reservoir, production and re-injection of geothermal aqueous phase can cause significant permeability variations due to local changes of effective stress. To assess the long-term performance of the reservoir, numerical modelling can be employed to investigate coupled impacts of these complex processes. Using the information acquired from laboratory experiments, a field-scale model was constructed to take into account the hydro-thermo-mechanical processes. The flow paths were tuned using results of tracer tests performed at the site. For the characterising the flow paths, the stress dependent fracture permeability was used. After calibrating the model with detailed structural mapping field data and laboratory measurements, the distributions of fracture permeability and porosity throughout the reservoir were mapped. The reservoir has two permeable layers separated with relatively lower fracture connectivity. Also, spatial distribution of fracture porosity can indicate the favourable conditions for mixing between injected and formation fluids. The outcome of this multi-scale study sheds light on the long-term performance of Hellisheidi geothermal reservoir, which would be utilised to guide further development of the region.