| dc.description.abstract | When an oil well is constructed it is important to cement the casing in place.The cement’s main objectives is to support the casing and ensure zonal isola-tion to prevent leakage of reservoir fluids to the surface. Primary cementingis therefore crucial for the well integrity. However, primary is considereda complex operation and needs to be carefully planed. There are differenttechniques for cementing, but the main goal is the same; place cement inthe annuls by safely displacing the drilling fluid. The most common wayof displacing is by pumping cement slurry, spacers and washers through theinside of the casing and back up the outside of the casing. However, reversecirculation cementing, is an alternative method, where the cement slurry,spacers and washers are pumped down on the outside of the casing. Reversecirculation cementing has been found to have some advantages while cement-ing lost circulation- and fragile zones compared to conventional cementing[1]. In contrast to conventional cementing, when preforming reverse circu-lation cementing the heavier cement slurry is on top of the lighter drillingfluid leading to a density-unstable ”heavy over light” displacement. Whilethe displacement mechanisms have been explored in depth for conventionalcirculation cementing where the denser cement slurry is below and displacingthe lighter mud upward, little is still known about the displacement efficiencyin reverse circulation cementing with the mechanically unstable configurationof cement slurry above and displacing lighter mud downward.We will in this study continue Camilla Bjørnsen’s work on density-unstableof Newtonian fluid in an annular space. The focus is on different flow ve-locities and density differences between displacing and displaced fluid. Inan experimental setup where colored heavy displacement fluid is separatedwith a valve above a lighter fluid and ran through a pipe is filmed to studythe displacement. The heavy fluid is mixed with NaCl as a weighting agentto achieve various density differences. Further, there is an outlet valve toregulate the flow velocity. Displacement with At of 0.0035, 0.01 and 0.02was ran with flow velocities of 0 mm/s, 10 mm/s, 20mm/s and 40 mm/s.Mixing, transverse flow and back flow was observed in all the experimentsconducted. However, with increasing flow rate the mixing and back flow wasreduced. Furthermore, an increase in At resulted in faster settling of heavyfluid but increased the mixing. | |
