In-situ formation stress determination using sonic logs and In- Borehole-Tomographic-Reconstruction of the near-borehole shear wave distribution

Abstract

For advanced borehole logging interpretation of cross-dipole shear wave sondes with `In-Borehole-Tomographic-Reconstruction' techniques an effective method for the determination of the mechanical stress distribution in the formation was developed. The method includes the reconstruction of the 3D-shear wave velocity distribution in the immediate surrounding area of the borehole formation with tomographic algorithms. The composition of the stress-induced shear wave velocity and comparison to the modelling results allow a quantitative interpretation. This log of the local formation stress anisotropy is excluded from both caliper-effects and the influences of shear wave velocity anisotropies caused by sedimentary effects. As examples, logs of ratios of the local minimal/maximal formation-stress amplitudes DSh/SH(z) were generated in a range of 0.86-0.99 for two gas production boreholes.