Acoustic signatures of sonar-based fracture diagnostics in horizontal wells

Post-fracturing fracture information needs to be acquired in a low-cost, efficient, and non-intrusive manner, which remains a significant challenge. Sonar-based fracture diagnostics conducted at the wellhead is emerging as a promising solution. It emits acoustic waves into the wellbore and interprets fracture parameters by monitoring reflected signals. However, the propagation mechanism of acoustic waves within the wellbore–fracture system remains poorly understood. This paper uses pressure acoustic simulations to examine wave propagation across different wellbore–fracture geometries and frequencies, focusing on pressure response, waveguide behavior, and modal interference. Results show that below 300 Hz, wave propagation remains stable regardless of curvature, whereas frequencies above 600 Hz exhibit modal dispersion, leading to phase delays and waveform distortion. When the fracture surface is modeled as a rock-impedance boundary, strong reflections occur at the perforation, and the reflected signal is particularly sensitive to the perforation diameter and fracture width. Meanwhile, acoustic waves that enter the fracture undergo multiple internal reflections and absorption along the fracture wall, making it difficult for them to return to the wellhead. Further simulations of a single-stage, multi-cluster fracturing scenario indicate that reflected signals can effectively reveal fracture initiation. A waveguide-based interpretation is introduced to explain the frequency-dependent behavior observed in the simulations, suggesting that modal interference may contribute to waveform distortion and localized amplitude increase at higher frequencies. These findings provide theoretical guidance for interpreting reflected signals and optimizing the selection of incident wave center frequency.