Characteristic of Pulse Displacement in Cementation of Vertical Well Washout

Displacement of residual fluid at the corners of washout is a problem during primary cementation. This is due to the nature of flow which will form favor flowing path in the displacement. In this paper, we propose a pulse displacement method in which injecting velocity changes with time according to specific functions. The purpose is to break the prior flowing path and increase the performance of displacement. Firstly, we investigate the difference between pulse displacement and constant velocity cementing. Then, we illustrate the influences of velocity function and washout geometry on pulse displacement performance. Results show that pulse displacement is of advantage in primary cementing of washout. Generally, pulse displacement induces strong and stable circular flow near the entrance of washout assisting sweeping displaced fluid. This circular flow becomes negligible when travels around 20 cm from the washout inlet when average velocity (v_o) is 1 m/s in this paper. However, the performance is similar for both pulse displacement and constant cementing at location far from the entrance. Furtherly, the parametric analysis shows that the displacement efficiency (DE) reduces with rising of average velocity and there is optimal value of velocity frequency (f) and amplitude (a) to have the best displacing performance. Also, combination with high value of f, v_o and a is benefit, but this will induce strong pressure vibration which may lead to downhole problem. Elongation of washout is of advantage for the displacement, but the enlargement of washout diameter has negative effect.