Fluid displacements for conventional and reverse circulation primary cementing

Abstract

The effective cementing of wells for oil and gas production, geothermal energy recovery and geological carbon storage is critical for ensuring well integrity and preventing fluid migration along the wellbore. This thesis investigates fluid displacement during primary cementing operations using both conventional and reverse circulation methods. Conventional cementing involves displacing drilling fluid with cementing fluids within the annulus around the casing from the bottom and toward the surface. Reverse circulation cementing involves the direct injection of cement into the annulus from the surface. This technique is advantageous for wells with weak or depleted formations because of reduced circulation pressures. Nevertheless, there are issues associated with unstable fluid densities caused by the fact that cement slurries are denser than drilling fluids. Inadequate removal of drilling fluid from the annular space between the casing and the wellbore or excessive mixing and contamination of the cement slurry can both impede the zonal isolation behind casings. If zonal isolation is broken, formation fluids can move freely along the wellbore and seep into shallower, more permeable formations or to the surface. To address these issues, this research employs both experimental and computational methods to analyze the displacement of cementing fluids under various conditions. Two different test setups were used in experimental studies: a reverse-circulation flow loop with downward imposed flow in the multiphase laboratory at the University of Stavanger (UiS) to mimic reverse circulation displacement and a conventional circulation flow loop with upward imposed flow in the complex fluid laboratory at the University of British Columbia (UBC) to simulate conventional circulation. The numerical simulations were performed using the OpenFOAM v2012 computational platform to explore the effects of a wider range of various parameters. Our investigations began by analyzing the impact of the density difference between two Newtonian iso-viscous fluids under stable, neutral, and unstable conditions as well as the potential stabilizing influence of imposed flow velocity. Subsequently, we broadened our research scope to include the effects of viscosity ratios on density-stable and densityunstable fluid displacement, encompassing both Newtonian and non-Newtonian fluids, as well as the effect of inclination and eccentricity of the annulus. Our findings suggest that reverse circulation cementing can cause increased mixing and potential contamination of the cement slurry due to unstable density configurations. High flow rates can stabilize the displacement front, while low flow rates exacerbate mixing and backflow. The viscosity ratio between the displacing and displaced fluids is crucial for effective displacement, with a more viscous displacing fluid generally improving displacement efficiency. Breaking the symmetry of the flow due to eccentricity or inclination was shown to further complicate the displacement process, highlighting the need for careful planning and optimization of cementing operations in such conditions. In conclusion, this thesis offers a comprehensive investigation into the dynamics of fluid displacement during primary cementing operations, specifically highlighting the complexities associated with density unstable displacement in reverse and conventional circulation cementing. The insights gained from this research provide a foundation for future advancements in cementing technologies, with the potential to significantly improve the reliability and safety of well construction in the oil and gas, geothermal energy, and carbon storage industries. The results can provide guidance for the development of fluids used in future reverse and conventional circulation displacement operations.