Title:

Design of a Convection Cell for a Downhole Heat Exchanger System in Klamath Falls, Oregon

Authors:

Tonya Boyd

Key Words:

downhole heat exchanger, direct use

Geo Location:

Klamath Falls, Oregon

Conference:

Stanford Geothermal Workshop

Year:

2009

Session:

Direct Use

Language:

English

File Size:

224KB

View File:

Abstract:

Downhole heat exchangers extract heat by two methods which are extracting heat from water flowing through the aquifer and extracting stored heat from the rock surrounding the well.

Although the interaction between the water in the well, water in the aquifer, and the rock surrounding the well is poorly understood, it is known that the heat output can be significantly increased if a convection cell can be set up in the well. Also, there must be some degree of mixing (i.e., water from the aquifer) continuously entering the well, mixing of the well water, and water leaving the well to the aquifer. There are three methods of inducing convection: 1) casing perforations, and 2) “pumping and dumping” and 3) installing a promoter pipe.

The promoter pipe is simply a pipe that is open at both ends that is placed in the well. The promoter pipe can be either placed along side or around the DHE, with the first being the more economical since a smaller promoter can be utilized. To set up a convection cell using a promoter pipe the locations of the perforations are important. The proper location of the perforations in a promoter produces the convection cell necessary to increase the temperature of the water over the length of the promoter. The top perforations are usually place below the lowest static water level and the lower perforations are placed in the location of the live water zone.

This paper will present three examples of downhole heat exchanger systems and how they were originally designed and then redesigned. The first system utilizes a promoter pipe which has perforations in three different locations and the second system utilized cased perforations, but the water level decreased and a promoter pipe was installed. The third system did not have perforations in the casing but was open at the live water area only. The three systems have been analyzed that were not getting the expected output from their systems. Solutions used to increase the output of the systems will be discussed.


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