Numerical simulation of geothermal resources: a critical overlook

The numerical simulation is a challenging part of the study of the geothermal resources. In this paper some of the main problems, criticalities and issues related to both simulation of reservoirs and ground thermal analysis are treated. Numerical simulation is successfully applied in several scientific fields and to solve a great number of engineering problems. Several applications in geothermal energy are possible, like reservoir engineering, ground heat exchange for HVAC (Heating, Ventilation and Air Conditioning) applications, environmental impact, hydrogeology. An interdisciplinary approach is necessary to pursue an aware and reliable utilization of the numerical models, due to the great complexity of the geothermal phenomenon. The different backgrounds involved are Numerical Analysis, Earth Sciences, Energy Engineering, Geochemistry. In this paper the authors discuss about the numerical simulation of the resource (generally considered): large spatial scale (reservoir engineering) and small spatial scale (shallow systems) examples are both illustrated. Particular attention is paid on these aspects: thermophysical parameters, boundary conditions, physical equations of the model, potential assessment, coupling of the “plant-reservoir” system. All of them are important to elaborate a critical and engineering point of view. For example, physical hypothesis and assumptions about the system are two of the main criticalities in the application of numerical approach; they have to be clear and reliable and their consequences should be known before the simulation is set up. The principle “trash in, trash out” should be known since the accuracy level of the input data is not always dealt as a problem, but it has a great influence on the results. The industry and market operators sometimes look at numerical models in a wrong way. Models should be related to the decisions about the utilization plant (heat/power) size. If the sustainability of a utilization project is seen from a global point of view, in which Environment, Economy, Technology are merged, the numerical models can be seen as the synthetic instrument to elaborate industrial strategies in relation to the resource durability. A discussion about when and why numerical models should be successfully implemented is carried on, also taking into account case studies and practical examples