Heat Transfer in a Low Enthalpy Geothermal Well

Abstract

The well from the University of Oradea campus is a typical low enthalpy geothermal well with multiple feed zones, about 3,000 m deep, 80˜85?C well head temperature, and about 30 l/s maximum artesian flow rate. This well was used to study the heat transfer between the geothermal fluid and the surrounding rock during artesian production.

The hydrodynamic and thermodynamic processes that occur during exploitation in the well and surrounding rock, from bottom to surface, are too complex for an exact analytical integration of the differential equations system. An analytical model based on simplifying assumptions was used to estimate the heat losses in the well at different flow rates. This model cannot be used to estimate the pressure and temperature fields in the rock. Furthermore, it shows that a quasi-steady regime is reached in the well after a very long production time, which is not confirmed by practice.

A 3-D numerical model was defined and used to simulate the heat transfer, hydrodynamic and thermodynamic processes in the well and in the surrounding rock along the entire well. The computer code used for the numerical simulation was TOUGH2, PC version. The model was used to simulate the evolution of the pressure and temperature fields in the well and in the surrounding rock during artesian production at different flow rates. It showed that the quasi-steady regime in the well is reached after a relatively short time of constant flow rate production.

The results of the numerical model have been compared with those of the simplified analytical model, showing that the numerical model not only yields more information, but it also offers a more accurate estimation of the hydrodynamic and thermodynamic processes in the well.