Shock-induced wave propagation over porous and fractured borehole zones: theory and experiments

Borehole waves are strongly affected by adjacent porous zones or by fractures intersecting the borehole. A theoretical description for both porous and fracture zones is possible based on the introduction of an effective borehole fluid bulk modulus, characterizing the wave attenuation via borehole wall impedance. This impedance can be calculated for both porous and fracture zones adjacent to the borehole, thus predicting borehole wave attenuation, transmission, and reflection over such zones. A shock tube setup generates borehole tube waves that are used for porous and fracture zone characterization. A PVC sample is used to introduce and vary fractures in a cylindrical sample. Shock wave experiments show that attenuation in boreholes adjacent to porous zones can be predicted by theory. The transmittivities of a borehole tube wave over 1 and 5 mm fractures are correctly predicted, thus showing the potential of borehole wave experiments for fracture detection and characterization.