Master of Science in Petroleum Engineering (MSPE)
Effective zonal isolation during primary cementing is only possible when drilling mud in the annulus is completely displaced with cement, while the spacers aid in this process. During the displacement process the rheological properties of fluids used and the operating conditions control the motion of different fluids interfaces; desired stable interfacial displacement leads to piston like motion. Computational Fluid Dynamics (CFD) tool with the Volume-of-Fluid (VOF) has been validated against experimental and used to conduct numerical experiments in a virtual well model consisting of 50 ft vertical section of 8.765" x 12.5" annulus having initially mud and this mud is swept by one annular volume of spacer followed by one annular volume of cement. The 50 ft section was further divided into five subsections each of length 10 ft and average values of quantities for these sections were used for further analysis. The mud and cement properties were kept constant and the spacer density, viscosity and displacement rate were the only controlling parameters to achieve the piston like displacement. The spacer density and viscosity were varied between water and cement with cement being the heaviest and most viscous fluid. Three Reynolds numbers of 100, 167 and 400 were simulated. Temporal variation of the mud volume fraction was used as an indication for the piston like interfacial displacement. For an ideal piston like interfacial displacement the mud fraction reduces sharply with minimum residual mud volume after the spacer sweeps through. A gradual mud reduction represents fluid fingering and the fluctuations in the mud fraction represent fluid mixing. The best displacement was observed when the spacer had the same density as mud while it has the viscosity similar to water. The displacement process was least effective when the spacer had the density equal to cement for all viscosity ranges. Based on the simulation results, a correlation was developed to find the final placed cement volume fraction in the annulus under similar fluid conditions, the utility of CFD based correlation is also presented. Further development of the correlation for varying spacer volume at other operating conditions may be needed to extend its applicability.
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Zulqarnain, Muhammad, "Simulations of the primary cement placement in annular geometries during well completion using computational fluid dynamics (CFD)" (2012). LSU Master's Theses. 2022.