Dipole logging in cased boreholes

Shear wave logging through casing can be challenging, especially when the surrounding formation is unconsolidated. This study identifies two possible causes of the problem using synthetic microseismograms, dispersion curves, signal processing scheme based on Prony’s method, and frequency‐dependent sensitivity coefficients with respect to the layers’ parameters. The first possible cause is eccentering of the tool when the cased hole is well bonded. The second possible cause is poor bonding, which is modeled by the presence of fluid annulus. An off‐center dipole source located in a well‐bonded cased hole generates a Stoneley wave that is poorly coupled to the surrounding formation and propagates at a velocity close to the compressional velocity of the borefluid. This Stoneley wave can obscure the formation shear wave signal associated with a slow (unconsolidated) formation. In a vertical well‐bonded cased hole, shear wave logging slow (unconsolidated) formations can be reliably performed despite the leaky c...