Denis P. Schmitt

Acoustic multipole logging in transversely isotropic poroelastic formations

The properties of the modes generated by multipole sources in a fluid‐filled borehole embedded in (radially layered) formations that include transversely isotropic poroelastic layers are investigated. These layers are modeled following Biot’s and homogenization theories, under the assumption that the principal axes of symmetry of both the transversely isotropic skeleton and the complex permeability tensor are parallel to the vertical axis of the borehole. A general formulation based on the Thomson–Haskell method accounts for any combination of fluid, elastic, and poroelastic layers, either isotropic or transversely isotropic. The investigation is achieved through the computation of dispersion and attenuation curves, and frequency‐dependent sensitivity coefficients with respect to the parameters. In the presence of a fast or slow radially semi‐infinite transversely isotropic poroelastic formation with an impermeable borehole wall, the shear‐wave transverse isotropy of the skeleton can be determined using t...

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...