Abstract
When identifying the conditions required for the sustainable and long-term
exploitation of geothermal resources it is very important to assess the
dynamics of processes linked to the formation, migration and deposition of
particles in geothermal systems. Such particles often cause clogging and
damage to the boreholes and source reservoirs. Solid particles: products
of corrosion processes, secondary precipitation from geothermal water or
particles from the rock formations holding the source reservoir, may
settle in the surface installations and lead to clogging of the injection
wells. The paper proposes a mathematical model for changes in the
absorbance index and the water injection pressure required over time. This
was determined from the operating conditions for a model system consisting
of a doublet of geothermal wells (extraction and injection well) and using
the water occurring in Liassic sandstone structures in the Polish Lowland.
Calculations were based on real data and conditions found in the
Skierniewice GT-2 source reservoir intake. The main product of secondary
mineral precipitation is calcium carbonate in the form of aragonite and
calcite. It has been demonstrated that clogging of the active zone causes
a particularly high surge in injection pressure during the fi rst 24 hours
of pumping. In subsequent hours, pressure increases are close to linear
and gradually grow to a level of ~2.2 MPa after 120 hours. The absorbance
index decreases at a particularly fast rate during the fi rst six hours
(Figure 4). Over the period of time analysed, its value decreases from
over 42 to approximately 18 m3/h/MPa after 120 hours from initiation of
the injection. These estimated results have been confi rmed in practice by
real-life investigation of an injection well. The absorbance index
recorded during the hydrodynamic tests decreased to approximately 20
m3/h/MPa after 120 hours.
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