Flow Characteristics and Response Surface Methodology‐Based Pressure‐Loss Prediction Models for the Reverse Circulation Converter in Double‐Wall Drill Pipes

ABSTRACT The reverse circulation drilling technology using double‐wall drill pipes has been widely applied in deep and complex formations due to its advantages of efficient cuttings transport, elimination of annular pressure loss, reduction of bottom‐hole pressure, and mitigation of lost circulation. As the core component linking the inner and outer annuli, the reverse circulation converter is crucial for ensuring smooth cuttings return. However, its structural design has largely depended on field experience, with limited systematic theoretical research on its flow characteristics. Based on the operating principle of the double‐wall drill pipe reverse circulation converter, this study establishes finite element models of the inner and outer annular flow domains to investigate their velocity and pressure distributions and underlying mechanisms. The influences of drilling fluid flow rate, density, and rheological parameters on annular pressure drop are also examined. Results show that, under identical conditions, the inner annulus exhibits higher maximum flow velocity and pressure drop than the outer annulus, along with significantly stronger and more extensive turbulent dissipation. Moreover, pressure drops in both annuli increase with drilling fluid flow rate, density, plastic viscosity, and yield stress. The sensitivity ranking of the total pressure drop to drilling fluid parameters is: flow rate > plastic viscosity > density > yield stress. Based on the numerical simulation results, second‐order response surface methodology (RSM) models were developed for rapid and accurate prediction of pressure losses in the inner and outer annuli. The model shows good agreement with the CFD simulation results, indicating its capability to accurately reproduce the numerical trends. The findings indicate that drilling fluid flow rate and plastic viscosity should be prioritized for optimization to effectively control pressure drop while satisfying operational requirements. This work provides robust theoretical guidance and practical predictive tools for structural optimization and engineering application of reverse circulation converters in double‐wall drill pipe systems.