Phase-field simulation of slurry displacement efficiency in borehole with a sudden contraction or expansion

Abstract

Due to the influence of geological and engineering factors, the irregular wellbore is commonly found in the field operation, resulting in a low slurry displacement efficiency. Compared with experimental and analytical methods, numerical simulation is an effective method to investigate the slurry displacement in a wellbore system with complex geometry. However, the present numerical simulation methods are usually unsuitable for the irregular wellbore because of the numerical dissipation triggered by the sharp curvature or difficulty in interfacing tracking. In this work, based on the fluid mass conservation equation, Navier-Stokes equation and Cahn-Hiliard equation, the phase-field mathematical models for slurry displacement is established. Through this method, the flow field and the evolution of the displacement interface in the irregular wellbore are analyzed in detail. The results show that, the disturbance of the irregular part can (1) generate the vortex within the expansion region or the downstream corner of the contraction, (2) cause unstable fluid-fluid interface, both of which result in poor displacement efficiency and subsequent poor cementation quality. Higher slurry's consistency coefficient, slurry's rheological index, the displacement rate or displacement time facilitate the improvement of the displacement efficiency in the irregular wellbore. The proposed phase-field method could avoid the numerical dissipation and track the fluid-fluid interface, and this method can also be applied for the displacement process in a channel with small size, such as slim hole or eccentric annulus due to the incorporation of surface force.