Unlocking the Flow: A Comparison of Off-Bottom Plug Placement Techniques in Well Abandonment

Abstract Plug and abandonment (P&A) of oil and gas wells are essential for the protection of the environment and public safety. In Western Canada, a common abandonment technique involves placing cement plugs along the wellbore, utilizing either the balanced-plug or the dump-bailing methods. The balanced-plug technique employs a constant injection flow rate, whereas the dump-bailing method relies on gravity to release cement slurry above a mechanical barrier. Ensuring minimal mixing of cement slurry with wellbore fluids is critical for the integrity of the abandonment process. In this study we develop three-dimensional hydrodynamic models of the two placement methods to compare the flow dynamics and mixing of the slurry and wellbore fluids. The primary difference between the placement methods is the slurry flow rate during the placement process. Our results reveal that the dump bailing approach leads to more extensive mixing of the slurry and wellbore fluids, especially as the distance between the cement release level and the barrier increases. The balanced plug method typically leads to the accumulation of a cement slurry with water content close to target specifications, contrasting with the dump bailing method, where the water content can vary significantly from the intended design.