In situ estimation of formation stress for Frac-strategy using sonic logging methods
There is a new interpretation method that has been developed for quantitative formation stress anisotropy borehole-logging using commercial cross dipole shear-wave sonic logs. Based on “In-Borehole-Tomographic Reconstruction” (IBTR) of the shear waves travelling through the immediate surrounding area of the borehole formation with the penetration depth as a function of the source receiver offset, a 3D-shear-wave velocity vs-distribution around the borehole was reconstruced. The formation stress anisotropy reflecting vs-distribution around a borehole is decomposed repeatedly in a quantitative minimal/maximal formation stress ratio for each depth. The method operates in both vertically and horizontally inclined boreholes.
As examples logs of ratios of the local minimal/maximal formation-stress amplitudes DrotSh/SH were generated for two gas production boreholes in the Rotliegend-Formation of northern Germany in a range of 0.86…0.99.