Oil wells are often abandoned when they become uneconomic. Normally, several cement plugs should be placed along cased wells to seal the producing formations. Proper placement protocols, especially for off-bottom plugs, are therefore required to prevent the seepage of oil. Often, heavy cement slurry is injected into wells filled with lighter wellbore fluids, through a centralised tube. To form the cement plug successfully, the injected cement slurry should accumulate at the target zone. Therefore, the current practices involve a major hydrodynamic challenge that can result in failing plugs.In a previous work, we had shown that injecting cement slurry in wellbore fluids can result in developing a cement finger that advects downstream the well. The finger then breaks and aids the formation of a density layer below the injection point. Consequently, the injected cement slurry starts accumulating to form the plug. These flow events were observed in a symmetrical flow domain. In this study, however, we consider different configurations of the injection process to investigate how the previously observed dynamics change. To that end, we consider the cement slurry and wellbore fluid as miscible fluids of different densities, and we model them as viscoplastic and Newtonian fluids, respectively. We conduct systematic numerical simulations based on representative hydrodynamic models using OpenFOAM, an open source CFD software, to identify favorable settings for placing off-bottom plugs.

Placing Off-Bottom Cement Plugs: Effects of Domain Geometry

Paper Proceedings: https://asmedigitalcollection.asme.org/OMAE/OMAE2021/volume/85116

OMAE 2021

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