107 2. Surface geophysical methods Figure 2.40 3D shear velocity model obtained with surface data (Saade et al., 2024). Conclusion In conclusion, we have introduced the physical properties of rocks and pore spaces, followed by a review of geophysical methods and their field applications, notably for geothermal energy. These methods play a crucial role in building 2D or 3D subsurface models: • gravity and gravity-gradiometry are sensitive to density variations, • magnetic methods respond to rock magnetization properties, including magnetic susceptibility and remanence, • electrical and electromagnetic (EM) methods capture resistivity variations, • seismic methods are influenced by both velocity and density variations. The selection of a geophysical method must be guided by the specific contrasts in petrophysical properties best suited to detecting the desired anomalies. Additionally, acquisition parameters need to be carefully chosen to target the appropriate depth, and both vertical and horizontal resolutions must be evaluated to ensure the method’s suitability for identifying anomalies of a given size. In many cases, combining multiple geophysical methods can improve the recovery of several physical rock properties simultaneously or enhance the capabilities of one method through the complementary strengths of another. For instance, the resolution of EM methods can be significantly enhanced through the integration of seismic methods (Alvarez et al., 2017).
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