Fluid experiments on the dump bailing method in the plug and abandonment of oil and gas wells

Abstract

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.