Dynamic modelling of geothermal systems

Abstract

The energy production capacity of hydrothermal systems is predominantly controlled by the reservoir pressure decline caused by the hot water production, which is in turn determined by the size of a geothermal reservoir, its permeability, reservoir storage capacity, water recharge and geological structure. More generally the capacity of all geothermal systems is also controlled by their energy content, dictated by their size and temperature conditions (enthalpy if two-phase). Hydrothermal systems can in most cases be classified as either closed, with limited or no recharge, or open, where recharge equilibrates with the mass extraction in the long run. Modelling plays a key role in understanding the nature of geothermal systems and is the most powerful tool for predicting their response to future production. Predictions are used to estimate their production capacity. Reliable models are also an indispensable part of successful geothermal resource management during utilization. In addition to the volumetric assessment method (static modelling) different methods of dynamic modelling are the main techniques used for geothermal reservoir modelling and resource assessment. The dynamic modelling methods apply simple analytical models, lumped parameter models or detailed numerical models to simulate the nature and production response of geothermal systems as well as to calculate future predictions. The modelling method applied should be determined by the purpose of a study and the data available for calibrating a model, as the time and cost involved are highly variable. All reliable models of geothermal systems, whether static or dynamic, should be based on an accurate conceptual model of the corresponding system. The results of geothermal system modelling may, moreover, lead to changes in their respective conceptual models.