| Title | Residual Strain Analysis By Neutron Diffraction On Granites From The Drilling EPS1 Of The Geothermal Site In Soultz-Sous-Forêts, France |
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| Authors | Carola Meller, Birgit Müller, Frank Schilling, Christian Scheffzük |
| Year | 2015 |
| Conference | European Geothermal Workshop |
| Keywords | |
| Abstract | The porphyritic granite of the soultz‐sous‐forêts geothermal site has been intensely altered during several hydrothermal alteration events. These events caused the dissolution of primary minerals and the precipitation of secondary minerals, e.G. Clay minerals (Figure 1). The presence of clay inside the rock matrix and fractured zones is affecting the mechanical strength. Mechanical contrasts in rock masses are supposed to change the ambient stress field locally (E.G. Valley 2007). The intrinsic strain parameters of the drill core samples reflect the local stress field to which the samples were exposed in‐situ. Strain develops in rocks and minerals as a response to the applied stress field. Rock deformation is reflected by a change in the lattice constants of the minerals, which can be measured by x‐ray scattering or by neutron scattering. The advantage of neutron scattering is its larger penetration depth into samples. For multiphase rock material, a large penetration depth (I.E. Large measured gauge volume) Is essential to measure a representative number of lattice constants from different mineral phases and directions. The applicability of neutron‐tof‐diffraction for strain analysis has been demonstrated earlier by siegesmund et al. (2008) And scheffzük et al. (2014). The determination of strain parameters of samples with different alteration grades will show inasmuch the intrinsic stress in altered samples with a large mechanical contrast to the surrounding rock deviates from the global stress field. |