Use of geodesy to discriminate deformation mechanics in geothermal reservoirs

Surface deformation is commonly observed phenomenon in various geothermal fields and reflects subsurface volume change due to shrinkage or dilation. However, faulting and fault reactivation induced by fluid injection (seismic and aseismic faulting) can also be a significant source of surface deformation. Monitoring subsurface deformation is useful in understanding reservoir behavior such as fluid mass and energy transfer and the evolution of transport characteristics. Moreover, detection of slip may allow a more precise understanding of injection-induced seismicity. We assess surface deformations (vertical displacement, surface tilt and horizontal strain) as signatures in two different modalities: (i) isotropic volume change (Mogi model) and (ii) injection induced shear offset (Okada model) and compare the results with both the resolution of current geodetic tools and existing observations of surface deformation. Comparison of predicted deformations with instrumental resolutions confirms that geodetic signals, especially tilt and strain, are indeed sufficiently large to describe reservoir evolution in detail and comparison to field data suggests probability of significant contribution of slip on surface deformation.