Geology Reference
In-Depth Information
Figure 5.
Permeability estimated from short-term well tests in fractured
crystalline rocks of Sweden (after Rutquist and Stephansson, 2003)
Even at depths of more than 1000 m, appreciable permeability are reported
in fractured rocks. For examples, Fetter (1988) reported higher permeabilites
from fractures at depths of 664 to 1669 m in granitic rocks of Illinois, USA.
Recent studies under the Continental Deep Drilling Project in Germany
(Kessels and Kuck, 1995) and HDR experiments in the Rhine Graben, France
(Gerard et al., 1996) also showed existence of good hydraulic interconnection
between adjacent boreholes through fractures even at a depth of more than
3000 m.
On the basis of above discussion, it may be summarized that although,
generally in fractured rocks a decrease in permeability with depth is observed
at several places but there is not much justification of such a universal rule.
Therefore, site-specific studies are necessary to establish any such variation.
Permeability is also influenced by mineral precipitation and dissolution
(Fig. 5).
Influence of Temperature on Permeability
Significant changes in rock temperature can occur due to natural weather
conditions viz. alternate freezing and thawing and due to man-induced
changes. Formation of ice in fractures will cause freezing and thawing. It
further causes extension of fractures and can also block the movement of
water producing pressure buildups. The influence of temperature on
