Investigation of displacement fluid performance for enhancing cementing quality in expanding section wellbores through filter cake removal

The expanding section wellbore presents significant challenges during drilling operations. In cementing displacement, residual filter cake and drilling fluid in the annulus are difficult to fully displace, leading to low efficiency and compromised cementing quality. Existing research primarily focuses on improving the drilling fluid displacement efficiency, with limited attention to filter cake displacement. This study addresses this gap by treating filter cake as a high-density, high-yield stress Herschel–Bulkley fluid and developing a three-phase fluid model for eccentric expanding section annuli. The effects of wellbore expansion ratio, displacement fluid flow velocity, density, and rheological properties on displacement efficiency are analyzed. The Ω vortex identification criterion is applied to explore how wellbore expansion influences displacement mechanisms. Results indicate that increasing the wellbore expansion ratio reduces displacement efficiency for both filter cake and drilling fluid due to the formation of larger and more numerous vortices. Optimal displacement fluid flow velocities are crucial, as excessively high velocity can lower efficiency. Higher displacement fluid density and yield stress enhance the displacement efficiency of both filter cake and drilling fluid, improving the overall cementing quality. Conversely, changes in the consistency coefficient and flow behavior index initially reduce efficiency but later improve it, driven by the interplay of flow state and drag force. These findings offer theoretical guidance for optimizing displacement fluid parameters and improving cementing practices in expanding section wellbores, addressing a critical aspect of enhancing wellbore integrity and operational performance.