Azimuthal anisotropy using shear dipole sonic: insights from the AIG 10 well, Corinth Rift Laboratory

Within the Corinth Rift Laboratory, dipole sonic data have been acquired in the AIG 10 well between depths 711 and 1004 m during three passes of a sonic logging tool at three different borehole fluid pressures. Specific sections of the well reveal clear characteristics of either moderate-to-large azimuthal anisotropy (9–25%) below the Aigion Fault, e.g., 779–784 and 809–816 m, with a fast-shear azimuth directed 105°, or homogeneous isotropic medium (i.e., 735–753 m) between the casing shoe and the fault. The presence of the fault is coincident with the identification of lower velocities over an interval of approximately 12–14 m. Analysis of the data reveals that the formation is not acoustically stress-sensitive to the 3 MPa differential pressure applied. Interpretation of the sonic data with complementary image logs suggests the anisotropy is due to intrinsic fractures and bedding, and the fast-shear direction 105° is consistent with the regional maximum horizontal stress. To cite this article: R. Prioul et al., C. R. Geoscience 336 (2004).