Three-Dimensional Hydrodynamics of Off-Bottom Plug Placement in Eccentric Wellbores

Abstract Successful plug and abandonment (P&A) operations in oil and gas wells are critical for environmental protection and cost-efficiency. A standard practice involves placing at least two plugs, with the upper plug (referred to as the off-bottom plug) playing a vital role in ensuring well integrity. In western Canadian practices, cement slurry is injected into wells filled with water during the initial stages of off-bottom plug placement. Ideally, the injector and wellbore are perfectly aligned, but in real-world scenarios, misalignment (eccentricity) is inevitable and can compromise plug integrity. In our previous studies, we developed a 2D model to simulate the early stages of off-bottom plug placement under eccentric conditions, revealing that water content on the narrow side of the annulus can significantly exceed target levels. Building on this foundation, the present study introduces a 3D model to provide a more comprehensive and representative analysis of the mixing dynamics between the injected slurry, modeled as a viscoplastic fluid, and the wellbore liquid, represented as a Newtonian fluid. The study investigates a range of eccentricity levels and compares the hydrodynamic behavior and water content predictions between 2D and 3D models. By delivering enhanced predictive accuracy, this work aims to optimize P&A operations, improving plug placement reliability and overall success rates.