Correcting sonic logs for shale anisotropy: a case study in the Forties field

摘要

Investigation and comparison of field-wide sonic logs acquired in the Forties field led to the discovery of significant anisotropy in the overburden Sele Shale formation due to strong layering. Propagation of compressional and shear waves at different velocities through anisotropic shales can have a pronounced impact on sonic log readings and their interpretation. These, in turn, can impact geomechanical models used for wellbore stability predictions, as well as completion design and seismic imaging. Neglect of shale anisotropy can contribute to drilling and completion failures, poor well-seismic ties, and incorrect well placements. To characterize anisotropy in the Forties field, Apache and Schlumberger formed a joint team and carried out an integrated geomechanical and geophysical study. This article presents an overview of the challenges, the methodology used to quantify anisotropy and correct sonic logs across the field, and results achieved through well-informed modifications to drilling parameters and practices.