文档介绍：Drilling methods for shallow
geothermal installations
Burkhard Sanner1 and Olof Andersson2
1 Institute of Applied Geosciences, Justus-Liebig-University
Diezstrasse 15, D-35390 Giessen, Germany
2 Department of Engineering Geology, Lund University of Technology
118, S-22100 Lund, Sweden
Introduction
Drilling is a very old technique, for water supply and for exploitation of mineral resources.
Water wells have been drilled in Egypt more than three millenia ago. Fig. 1 shows an example
of a quite sophisticated, hand-operated drill rig used in China to drill several hundred meter
deep in a few month.
Fig. 1: Chinese percussion boring (after Chugh, 1985)
Today, a variety of mechanised drilling equipment is on the market and in use. The size range is
from small augers for post-holes few meters deep to the deepest borehole on Kola peninsula in
Russia with a depth of more than 12 km. Economic considerations as well as technical
problems restrict the drilling depth for shallow geothermal applications generally to around
100 m. In recent times, also deeper holes have been drilled for borehole heat exchangers (BHE)
with ca. 250 m depth, and holes in the 400-m-range are in preparation in Switzerland.
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Although a deeper hole provides access to slightly higher temperature, the increasing problems
with insertion of heat exchanger, grouting and static pressure have to be solved.
For vertical ground heat exchangers, a distinction has to be made between two basic ways of
installation:
· Direct pressing or ramming of the heat exchanger into the ground (in soft ground only)
· Insertion of the heat exchanger in a borehole drilled beforehand
Boreholes can be drilled under almost any subsurface condition From site to site, an optimum
choice for type and installation method is necessary according to the geological situation.
Basic drilling methods
For shallow holes down to app. 100 m, not every drilling method is suitable. Hytti (1987)
presents