Wellbore mechanical properties have long been used to model formation responses when planning highly deviated wells, horizontal wells and fracture treatments. Now, with the inclusion of the maximum stress direction and horizontal stress ratio, a complete model of the formation response to stress can be obtained.
The fact that shear waves will split and become polarized parallel and perpendicular to natural fractures is well documented. The fact that the fast shear wave is oriented in the direction of the maximum horizontal stress is also well documented. Cross dipole shear data from a digital sonic tool is processed to obtain oriented fast and slow shear waves. The theory of shear anisotropy processing is reviewed and the quality control and interpretation of the resulting anisotropy log are discussed.
For this case study, azimuthal anisotropy data obtained from dipole shear sonic logging in Western Venezuela is used to determine the direction of maximum horizontal stress and horizontal stress ratio. This information is then used to determine the oriented mechanical properties. These mechanical properties are presented in the form of an oriented wellbore stability analysis.
When the information obtained from dipole shear sonic anisotropy logging is used in the planning of horizontal wells, deviated wells and fracture treatments the overall cost of the well can be reduced. Using this information, efficiency can be increased and potential problems can be avoided.