Modeling of Acoustic Fields and Experimental Validation of Flexural Guided Wave Modes in Fluid-Constrained Dual-String Pipe Systems

Fluid-filled dual-string pipe systems are widely utilized in the petroleum industry. Taking the example of a concentric structure composed of production tubing and cemented casing strings, the bonding integrity of the outer string plays a critical role in ensuring safe extraction operations. This study conducts theoretical modeling and acoustic simulations of flexural mode guided waves in dual-cased wells, with a focus on comparing modal responses under varying media conditions in the B annulus of the outer casing. Theoretical and experimental results demonstrate that when the B annulus is fluid-filled, significantly more flexural modes (particularly higher-order modes) are excited compared to cemented scenarios. These higher-order flexural modes can be effectively utilized as acoustic indicators to evaluate annular bonding quality. The findings provide a theoretical foundation for non-invasive integrity evaluation in multi-string well systems.