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 aquifer. Although this peculiarity reduces installation costs it also imposes limits on the heat ¯ow withdrawable (generally less than 100 kW), and, therefore, on the use of DHEs in small applications such as greenhouses, small buildings or thermal baths. For this reason DHEs are mainly used in super®cial geothermal aquifers (up to 30mdepth), usually with liquid-phase water at temperatures greater than 60 C. A study has been made of the in¯uence of the position of the casing slotted section within an aquifer on the heat withdrawal rates using DHEs. This study numerically simulates an aquifer using the ®nite-element method to determine the heat ¯ow that can be withdrawn by the DHE when the slotted section position is varied within a geothermal aquifer. The simulations carried out also enable us to determine the in¯uence of the main characteristics of the aquifer and the extraction plant on the design of the tube casing slotted section. On the basis of the numerical results obtained, a particular con®guration of slotted section is proposed where this is subdivided into di€erent sections, one placed in the lower part of the aquifer and the other in the upper part. The results obtained have shown that this con®guration optimizes the heat ¯ow drawn by the DHE from the geothermal aquifer. # 2001 CNR. Published by Elsevier Science Ltd. All rights reserved.