A wellbore flow model for large-size-disparity annulus based on downhole flow-splitting tool

Large-size-disparity annulus, often generated by staged cementing, causes severe flow maldistribution during drilling, undermining safe and efficient operations. A downhole flow-splitting tool offers a promising solution by redistributing drilling fluid between annular sections. However, existing studies have neither established segmented wellbore flow models capable of capturing variable flow distributions nor addressed the local hydraulic losses introduced by flow-splitting tools. In this study, surface experiments were conducted to measure the local resistance coefficients of flow-splitting tools with different diversion port diameters. Based on these data, a segmented wellbore flow model was developed using a fully implicit finite-difference method, explicitly accounting for flow rate, pressure, and temperature variations with depth induced by splitting. A case study of ZS102 Well was then carried out, covering a flow-allocation scheme design, diversion port sizing, and field drilling analysis. Results show that the local resistance coefficient of the tool remains nearly constant (ζ ≈ 0.4688) across a diversion port diameter range of 4–18 mm. Model validation against experimental data yielded maximum relative errors below 5%. Application to ZS102 Well demonstrates that activating the tool reduces bottomhole pressure from 86.57 to 80.97 MPa and standpipe pressure from 31.98 to 9.96 MPa while maintaining adequate borehole cleaning. These results confirm the tool's practical value in mitigating lost-circulation risks and improving hydraulic efficiency in complex wellbore geometries. The findings deliver a robust theoretical foundation for the flow-allocation scheme design, tool optimization, and the advancement of intelligent downhole flow-splitting technologies in challenging drilling environments.