Abstract: When displacing the cementing of horizontal wells, it is usually difficult to realize the replacement in turbulent flow because of instrumental limitation. In laminar flow, however, the transport mechanism of two-phase flow in the eccentric annulus can be quite complex. Based on the computational fluid dynamics method, we developed a geometric and numerical model, tracked the displacement interface of two-phase flow using the fluid volume method, and analyzed the transport mechanism of displacing fluids in the eccentric annulus of horizontal wells under various displacing flow rates. The following conclusions are drawn from the results:(1) With a low eccentricity, one-time use of isolation fluid can realize 90% displacing efficiency. When the eccentricity is greater than 0.5, the displacing efficiency becomes relatively small. In this case, increasing the amount of isolation fluids cannot further increase the displacing efficiency; (2) Considering the severe eccentricity of the casing, reducing the flow rate from 1.0 m/s to 0.2 m/s can help stabilize the interface and results in 6.8%higher displacement of drilling oil. Furthermore, this approach can also resolve the retention issue on the narrow side and pointing issue on the wide side; (3) The cementing displacement process in the eccentric annulus of horizontal wells is affected by multiple factors, including the eccentric effect, gravity effect, and viscous effect. These factors interact and inhibit with each other. Therefore, a reasonable design of cementing process parameters based on the actual well conditions on site can not only improve cementing quality, but also reduce cost and increase efficiency.

Key words: horizontal well, eccentricity, displacement flow rate, displacing efficiency, flow interface