Low-temperature hydrothermal activity in Iceland is
apparently mostly controlled by dikes and fractures.
Conventional methods of production data analysis are not
readily applicable in cases of heterogeneous/anisotropic
fracture dominated hydrothermal systems. Moreover, the
dikes and fractures may control the heat uptake mechanism
of low-temperature activity.
The free-surface response functions of analytical
reservoir models are presented and methods for analyzing
production data on the basis of such models are
developed. Based on a homogeneous and isotropic half-space
model apparent permeability estimates of 0.7
millidarcy are obtained for two low-temperature systems
in Tertiary strata in N-Iceland whereas estimates of 5-20
millidarcy are obtained for two systems in Quaternary
strata in SW-Iceland. A vertical two-dimensional flow
model is, however, more consistent with the apparent
linear dike/fracture control of many hydrothermal systems
and results in higher permeability estimates.
Methods of simulating long term production data by
simple lumped capacitor/conductor ladders based on only
production/drawdown data are developed and the responses
of analytical as well as real systems are shown to be
easily simulated by such simple systems. The parameters
of simulation ladders also provide information on global
hydrological characteristics of hydrothermal systems.
A possible dike/fault controlled source mechanism of
low-temperature activity in Iceland is considered. This
process involves the downward migration of open sections
of unwelded quasi-vertical fractures resulting from
cooling and contraction of the adjacent rock, in
conjunction with vertical heat transfer in the fracture.
The rate of downward migration is estimated and found to
depend very strongly on the magnitude of the horizontal
regional stress. Stress conditions may therefore
determine whether a low-temperature system can evolve at
a given location as well as determine the intensity of
hydrothermal activity. / Graduation date: 1986
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/29135 |
| Date | 06 June 1985 |
| Creators | Axelsson, Gudni |
| Contributors | Bodvarsson, Gunnar |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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