BOREHOLE STONELEY WAVE PROPAGATION ACROSS PERMEABLE STRUCTURES1

Abstract

AbstractThis study investigates the propagation of borehole Stoneley waves across permeable structures. By modelling the structure as a zone intersecting the borehole, a simple 1D theory is formulated to treat the interaction of the Stoneley wave with the structure. This is possible because the Stoneley wave is a guided wave, with no geometric spreading as it propagates along the borehole. The interaction occurs because the zone and the surrounding formation possess different Stoneley wavenumbers. Given appropriate representations of the wavenum‐ber, the theory can be applied to treat a variety of structures, including a fluid‐filled fracture. Of special interest are the cases of permeable porous zones and fracture zones. The results show that, while Stoneley wave reflections are generated, strong Stoneley wave attenuation is produced across a very permeable zone. This result is particularly important in explaining the observed strong Stoneley wave attenuation at major fractures where it has been difficult to explain the attenuation in terms of the single planar fracture theory. In addition, by using a simple and sufficiently accurate theory to model the effects of the permeable zone, a fast and efficient method is developed to characterize the fluid transport properties of a permeable fracture zone.