Injecting A Viscoplastic Fluid In A Channel Filled With A Lower Density Newtonian Fluid: Effects Of Premixing

Abstract

Oil wells are normally abandoned using several cement plugs. Plugs above the deepest one are called off-bottom. The balanced plug method is the most used technique to place off-bottom plugs. In most cases, the initial stage of the balanced plug method includes injection of the cement slurry in cased wells. A tube smaller than the casing is inserted to the depth where the plug should be placed. Cement slurry is then injected through the tube into the cased wellbore, that is initially filled with wellbore liquids. Under field conditions, mixing of the fluids inside the injector is inevitable.In this study, we model the above cement injection process in a representative two-dimensional domain. We explore the effect of fluids premixing inside the injector on the dynamics below it. We first consider an idealized case where the displacing fluid fills the injector initially. To model the fluids premixing, we consider three other cases where the injector is initially filled with the displaced fluid, a buffer layer of both fluids and a combination of both.Our preliminary results show that the injection in the idealistic case results in a cement finger developing below the injector. The finger then breaks due to an interfacial instability. As a result, a mixed layer forms below the injector. The premixing of fluids in the injector result in qualitatively similar dynamics as above. Mixed fluids advect below the injector. Shortly after, unsteady dynamics, within the injector or below it, facilitate the formation of a mixed layer below the injector.