4The In Salah CO 2 storage project in Algeria has injected over 3 million 5 tonnes of carbon dioxide into a water filled tight sand formation. Interfer-6 ometric Synthetic Aperture Radar (InSAR) range change data revealed a 7 double lobbed pattern of deformation that has been modeled as the opening 8 of a sub-vertical fracture, or damage, zone. The location and geometry of 9 the linear feature were subsequently verified using a seismic reflection sur-10 vey. The elastic properties of the fracture zone, including anisotropic Poisson 11 ratio (ν), Young's (E) and shear (G) moduli, were estimated from coupled 12 geomechanical and hydrological modeling of surface deformation and pres-13 sure variations in the injection well. The elastic moduli reflect the fracture 14properties after CO 2 flow through the fracture zone. Thus, the seismic sig-15 nature of the fracture zone could be used for monitoring the CO 2 plume.
16Using the estimated fracture model, we built two and three dimensional mod-17 els consisting of an anisotropic fracture zone embedded within an isotropic 18 background. Finite-difference modeling of seismic shot gathers allows us to 19 estimate the effects of scattering from the fracture zone, potentially further 20 constraining the geomechanical model. From the seismic modeling results, 21 we find diffracted waves, induced by the fracture zone, which behave similar 22 Page 3 of 57to point source diffractions. This modeling is intended to guide a search for 1 diffraction events in the 3D surface seismic field data. The modeling results 2 indicate that using the moduli estimated from geomechanical modeling, frac-3 ture scattered events would be 100 times lower amplitude than the interface 4 reflections, and thus would be hard to detect. While diffracted waves are ob-5 served in the field data, which may imply the need for revision of the fracture 6 model, including shape and elastic moduli, we are not able to match the field 7 observation whith our modeled events. This work presents a frontier study 8 on the integration of geomechanical and geophysical methods at the In Salah 9 site as a means to test the estimate of the subsurface CO 2 flooded fracture 10 properties.
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