Borehole Stoneley Wave Propagation across Permeable Structures: Comparison between Theory

The attenuation of borehole Stoneley waves across a permeable structure (e.g., fractures or fracture zone) is correlated with the permeability of the structure. Using a simplified Biot theory, the structure can be modelled as a permeable porous layer intersecting the borehole. In order to study the effect of such a structure on Stoneley waves and to evaluate the theoretical model, we performed laboratory experiments using ultrasonic borehole models. The porous layer model is made of fine-grained sands with high permeability and porosity. The experiments are carried out with three saturant fluids: water, alcohol, and glycerol. The iso-offset Stoneley waveforms are recorded by moving the source and receiver across the porous layer. In this way, robust estimates of Stoneley wave transmission coefficients are obtalned. The experimental transmission coefficients are compared with the theoretical coefficients calculated using the borehole and permeable zone parameters. There is good agreement between theoretical results and experimental results. For low viscosity fluid water and ethyl alcohol, the agreement is very good. For high viscosity fluid, glycerol, the agreement is fair with the experimental Stoneley attenuation higher than the theoretical value.