Optimizing the position of the tube casing slotted section for geothermal wells with a downhole heat exchanger

The use of downhole heat exchangers (DHE) in the exploitation of geothermal resources is characterized by an absence of mass withdrawal from the aquif er. Although this peculiarity reduces installation costs it also imposes li mits on the heat flow withdrawable (generally less than 100 kW), and, there fore, on the use of DHEs in small applications such as greenhouses, small b uildings or thermal baths. For this reason DHEs are mainly used in superfic ial geothermal aquifers (up to 30 m depth), usually with liquid-phase water at temperatures greater than 60 degreesC. A study has been made of the inf luence of the position of the casing slotted section within an aquifer on t he heat withdrawal rates using DHEs. This study numerically simulates an aq uifer using the finite-element method to determine the heat flow that can b e withdrawn by the DHE when the slotted section position is varied within a geothermal aquifer. The simulations carried out also enable us to determin e the influence of the main characteristics of the aquifer and the extracti on plant on the design of the tube casing slotted section. On the basis of the numerical results obtained, a particular configuration of slotted secti on is proposed where this is subdivided into different sections, one placed in the lower part of the aquifer and the other in the upper part. The resu lts obtained have shown that this configuration optimizes the heat flow dra wn by the DHE from the geothermal aquifer. (C) 2001 CNR. Published by Elsev ier Science Ltd. All rights reserved.