NUMERICAL MODELLING OF FLUID FLOW AND HEAT TRANSFER IN A DUALPOROSITY DOMAIN IN THE SHALLOW ZONE OF THE NESJAVELLIR GEOTHERMAL SYSTEM

Abstract

A numerical model of the warm wastewater re-injection zone was developed for the Nesjavellir geothermal field in Iceland. A detailed shallow 3D geological model was built to constrain the numerical model, with a dual-porosity based on Multiple Interactive Continuum (MINC) was considered as fracture model. The calibration method used was underground water temperature data measured between 1998 - 2019, along with tracer test data carried out in the area between 2018 - 2019. The temperature simulation showed acceptable results matching with the temperature field, and the tracer model closely matches the overall tracer return in the most of the monitoring stations. With the model calibrated we proceeded to simulate two future scenarios for a period of 20 years. The first scenario assumes that the injection continues, and in the second scenario the injection is completely stopped. The numerical model in this study allowed a better characterization of the fracture matrix interface and the porosity of postglacial lava flows, along with a clearer understanding of the connections between injection wells and monitoring stations, providing solutions for sustainable management of the geothermal resource and the surrounding environment.