Advanced well model for superhot and saline geothermal reservoirs

Abstract

We present a new well model aimed at simulating deep and superhot geothermal wells within reservoir-scale flow models. The model uses a classic multi-segment approach to solve the well hydrodynamics but also includes several important features significantly expanding its capabilities. Firstly, we use thermodynamic tables allowing us to accurately model fluids at all relevant pressures, temperatures and salinity conditions up to magmatic conditions. The well model can account for the transport of dissolved NaCl salt and its potential precipitation in the form of halite. Secondly, the model includes an air phase and incorporates the transient displacement of the air-water interface in the well. This allows us to simulate the starting of the well using the air pressurization technique. Lastly, the well model is coupled to an unstructured reservoir grid on which magma bodies and feed zones can be explicitly represented. This paper introduces the technical details of the well model and presents several applications showcasing what insights could be gained concerning the performance of deep geothermal wells. We conducted two sets of simulation: first, we simulated a deep resource resulting from strongly enhanced heat flux with a well and a single feedzone; we assessed the effects of the feedzone's permeability, temperature and salinity on well starting and initial performance. In a second set of simulations, we used a more realistic hydrothermal system, driven by a magmatic intrusion. From the results we illustrate examples of which factors control the ability of the well to self-start, if and how air pressurization can aid starting wells, how production from a supercritical resource created near a magmatic intrusion may evolve over up to 200 years, and how halite precipitation may rapidly clog the well in case of production from saline superhot resources.