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Titel |
Numerical simulations of saltwater displacement via fault systems due to exploitation of the subsurface |
VerfasserIn |
Maria Langer, Elena Tillner, Thomas Kempka, Michael Kühn |
Konferenz |
EGU General Assembly 2015
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 17 (2015) |
Datensatznummer |
250111872
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Publikation (Nr.) |
EGU/EGU2015-12019.pdf |
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Zusammenfassung |
Injection of fluids into deep saline aquifers induces an increase in pore pressure in the storage
formation, and thus displacement of resident brines. Upward brine migration into shallower
aquifers via hydraulically conductive faults may therefore lead to unwanted salinization
of potable groundwater resources. In the present study, we investigated different
scenarios for a prospective storage site close to the city of Beeskow in the Northeast
German Basin by using a representative 3D regional-scale model (100 km x 100 km x
1.34 km) that includes four regional fault zones. The focus was on assessing the
impact of fault length and permeability as well as model boundary conditions on the
potential salinization of shallow groundwater resources. Moreover, the effects of an
overlying secondary brine-bearing reservoir as well as varying initial salt-freshwater
boundaries were investigated. We employed numerical simulations of brine injection as
a representative fluid based on an example case study discussed by Tillner et al.
(2013).
Our simulation results demonstrate that pressure build-up within the reservoir
determines the fluid rates and duration through the faults, and hence salinization of
shallower aquifers. Application of different boundary conditions proved that these
have a crucial impact on reservoir fluid displacement. If reservoir boundaries are
closed, the fluid displaced via the faults into the shallow aquifer corresponds to the
overall injected fluid mass. In that case, fault length and permeability as well as the
presence of an overlying secondary reservoir have only temporal effects on brine
migration. A fault zone with a hydraulically conductive segment of only two kilometres
length causes brine flow into the shallow aquifer of 330 years, which is thus five
times longer compared to the case with four faults open over their entire length of
193 km. The presence of an overlying secondary reservoir leads to an additional
retardation of brine inflow into the uppermost aquifer up to a factor of three. If the
reservoir boundaries are open, salinization is considerably reduced. In the presence of
a secondary reservoir, 33 % of equivalent brine mass migrates into the shallow
aquifer, if all four faults are completely hydraulically open, whereas the displaced
equivalent brine mass is only 13 % if accounting for a single fault of two kilometres
length. Without the secondary reservoir, 66 % of the brine mass is displaced in the
four fault and about 30 % in the 2 km single fault cases. Taking into account the
considered geological boundary conditions, the brine mainly originates from the
upper 16 m to 300 m of the investigated faults, and hence the initial salt-freshwater
boundary present in the fault is of high relevance for the resulting shallow aquifer
salinization.
The present study successfully demonstrates that a quantification of brine displacement
using numerical simulations is feasible at regional scale.
Tillner, E., Kempka, T., Nakaten, B., Kühn, M. Geological CO2 Storage Supports
Geothermal Energy Exploitation: 3D Numerical Models Emphasize Feasibility of Synergetic
Use (2013) Energy Procedia 37:6604-6616. doi:10.1016/j.egypro.2013.06.593. |
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