Numerical Simulation Of Annulus Cementing Dynamic Displacement Interface

In cementing process, replace efficiency is very important to cementing quality. For replacement, there is a consistency of conclusion that is turbulent flow is better than Laminar flow or Plug flow.But in many cases.people have to use the laminar replacement for the low formation pressure. Cementing laboratory experiments show that, we cannot achieve a dynamically stable interface many times. But it should be achieved according to mechanics analysis. The limitations on annulus length of test cannot be carned out on the more long distance interface, so it is necessary to use numerical simulation method to replace interface for long-distance study.Based on the non Newtonian fluid mechanics basic theory and basic control equation of fluid motion, and combined with the reconstruction of the VOF method in the free interface a two-phase displacement flow model is established. Then the interface of long-distance flow is be simulated in CFD software FLUENT. Respectively to simulate the different degree of eccentricity, density contrast, speed, fluid rheological properties under the condition of interface in the process of displacement. According to simulation results, the changing process of interface and the velocity distribution on the interface are done. The influence of the above factors on the interface and the displacement efficiency under different interface are achieved. After the start of the replacement the length of the interface is constantly stretched, the interface will reach fluctuated in a range of dynamic stability or absolute stability based on the positive density contrast, and be moved forward. In concentric annulus, the interface is absolute stability as long as the density contrast is positive. In Eccentric annulus, the absolute stability condition is high density contrast, otherwise a dynamic stability interface would be achieved. Under the negative density contrast interface are unable to achieve stability. From the effects of interface, the descending order of the degree of eccentricity, the density contrast, replaced speed and fluid rheological properties. The decrease of casing eccentricity, the density contrast, displacement speed, the value of n and k of the displacement fluid, and reduced by the value of n and k of the drilling fluid, which can reduce the dynamic interface length and improve the efficiency displacement. In Eccentric annulus, there is tangential velocity on the interface between wide and narrow gap clearance, the tangential flow caused by the wide gap fluid to narrow gap fluid extrusion was the mainspring of narrow gap interface moving forward.Comparing simulated results with lab experimental ones, the conclusions obtained in this paper are highly similar with the experimental results which based on short distances annulus. The simulation results have a very good role in guidins on annulus cementing.