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| Titel |
Estimating the reactivation potential of existing fractures in subsurface granitoids from outcrop analogues and in-situ stress modeling: implications for EGS reservoir stimulation with an example from Meiningen (Thuringia, Central Germany) |
| VerfasserIn |
Kamil Ustaszewski, Norbert Kasch, Melanie Siegburg, Payman Navabpour, Manuel Thieme |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250088920
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| Publikation (Nr.) |
 EGU/EGU2014-3099.pdf |
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| Zusammenfassung |
| The southwestern part of Thuringia (central Germany) hosts large subsurface extents of
Lower Carboniferous granitoids of the Mid-German Crystalline Rise, overlain by an up to
several kilometer thick succession of Lower Permian to Mid-Triassic volcanic and
sedimentary rocks. The granitic basement represents a conductivity-controlled (‘hot dry
rock’) reservoir of high potential that could be targeted for economic exploitation as an
enhanced geothermal system (EGS) in the future. As a preparatory measure, the federal states
of Thuringia and Saxony have jointly funded a collaborative research and development
project (‘Optiriss’) aimed at mitigating non-productivity risks during the exploration of such
reservoirs.
In order to provide structural constraints on the fracture network design during reservoir
stimulation, we have carried out a geometric and kinematic analysis of pre-existing fracture
patterns in exposures of the Carboniferous basement and Mesozoic cover rocks within an area
of c. 500 km2 around the towns of Meiningen and Suhl, where granitic basement and
sedimentary cover are juxtaposed along the southern border fault of the Thuringian Forest
basement high. The frequency distribution of fractures was assessed by combining
outcrop-scale fracture measurements in 31 exposures and photogrammetric analysis of
fractures using a LIDAR DEM with 5 m horizontal resolution and rectified aerial images at 4
localities. This analysis revealed a prevalence of NW-SE-trending fractures of mainly
joints, extension veins, Permian magmatic dikes and subordinately brittle faults
in the Carboniferous granitic basement, which probably resulted from Permian
tectonics.
In order to assess the reactivation potential of fractures in the reservoir during a
stimulation phase, constraints on the current strain regime and in-situ stress magnitudes,
including borehole data and earthquake focal mechanisms in a larger area, were
needed. These data reveal a presently NW-SE-trending maximum horizontal stress
SHmax and a strike-slip regime (Heidbach et al. 2008). In-situ stress magnitudes at a
reservoir depth of 4.5 km were calculated assuming hydrostatic pore pressures and
frictional equilibrium along pre-existing fractures. Our estimates allow predicting that
NW-SE-trending fractures in the reservoir would probably be reactivated as dilational veins
during stimulation. In order to ensure that the stimulated rock volume is as large as
possible and injected fluids circulate along newly-formed fractures rather than other
pre-existing fractures, hydraulic fracturing at reservoir depth should follow a well
trajectory parallel to the minimum horizontal stress Shmin, i.e.subhorizontal and
NE-SW-oriented.
References:
Heidbach, O., et al., 2008, World Stress Map database release 2008, doi:10.1594/GFZ.WSM.Rel2008. |
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