Plug and abandonment (P&A) operations prevent oil and gas leakages from hydrocarbon zones to different formations, freshwater underground resources, and the surface. Cement plugs that are used in P&A operations play a crucial role in impeding reservoir fluid migrations. The dump bailing method is one of the common methods of the cement plug placement in which a determined volume of cement is dumped by a bailer on a bridge plug in the wellbore, to replace the in-situ fluid while filling the wellbore and the annular region outside the bailer. In this paper, we experimentally investigate the placement of a heavy fluid to remove and replace an in-situ light fluid in an inclined closed-end pipe, representing the dump bailing method from a fluid mechanics perspective. The two fluids are Newtonian and miscible, and they have a density difference. We examine the effects of the injection fluid properties and flow parameters, on the fluid placement efficiency, the degree of mixing and quality of the placement. We use high-speed imaging and non-intrusive measurement techniques to provide ample placement flow characterizations. Our results show that the most efficient heavy fluid placement ensues from smaller dumping heights. Also, increasing the density and viscosity differences strengthens the efficiency of the in-situ fluid removal. In addition, the influence of a higher rate of injection is more discernible in smaller dumping heights, where it results in the removal of the light fluid promptly from the flow domain, with minimum mixing and placement time. The results are in general helpful for improving the quality of the cement plug placement in P&A operations.

即插即弃（P＆A）操作可防止油气从碳氢化合物层泄漏到不同的地层，淡水地下资源和地表。在P＆A作业中使用的水泥塞在阻止油藏流体运移方面起着至关重要的作用。排污法是水泥塞放置的常用方法之一，在该方法中，由固定锤将确定体积的水泥倾倒在井眼中的桥塞上，以在填充井眼和环形区域的同时置换现场流体委托人外。在本文中，我们通过实验研究了重油的放置，以去除和替代倾斜的封闭端管道中的原位轻油，从流体力学的角度代表了转储卸油方法。两种流体是牛顿流体和可混溶的，并且它们具有密度差。我们检查了注入流体特性和流动参数对流体放置效率，混合程度和放置质量的影响。我们使用高速成像和非侵入式测量技术来提供足够的贴装流特征。我们的结果表明，最有效的重油放置来自较小的倾卸高度。而且，增加密度和粘度差会增强原位流体去除的效率。此外，在较小的倾卸高度下，可以更清楚地看到较高注入速度的影响，从而可以在最小的混合和放置时间的情况下，从流域中迅速清除轻质流体。这些结果通常有助于提高P＆A作业中水泥塞放置的质量。