dc.description.abstract | Researches in the industry have always ascertained that mud channels affect the two principal
objectives of primary cement job; zonal isolation and structural support. This can lead to envi-
ronmentally, operationally hazardous well. Velocity profile of cement slurry flow, due to no-slip
boundary condition, is among the reasons behind mud channeling. This study aims at cement
displacement efficiency based on investigation of operational parameters and conditions that
control the nature of velocity profile. The effects of cement rheology, flowrate, flow regime,
pipe roughness, and contact time are analyzed through model equations and experiments for
laminar and turbulent flow of Newtonian, Bingham plastic, and Power-law fluids in a horizontal
pipe. Eulerian method of flow description is employed to locate fluid interface through time
along a radially discretized control volumes.
The respective effect of viscosity and flow rate on displacement efficiency was studied both
under turbulent and laminar flow conditions. Increase in flowrate followed by surpass of critical
Reynolds number brings robust displacement efficiency. Around 15% theoretical displacement
efficiency superiority of turbulent regime over laminar flow was recorded at the tested conditions
for both Newtonian and Power-law fluids. After turbulent flow is reached, an increase of flow
rate brought slight decrease of efficiency for Bingham and Power-law fluids while efficiency
of Newtonian fluid still increases. The main reason is shear thinning behavior of the non-
Newtonian fluids which leads spearheading at high rate. A decrease of viscosity that brings
higher displacement efficiency when critical Reynolds number is exceeded. However, decrease
of apparent viscosity during laminar flow of Bingham fluids resulted in decrease of efficiency
as it led to narrow plug flow radius. Pipe roughness and contact time increased efficiency.
Results of this study suggested that cement should necessarily displace mud in turbulent
flow. Laminar cement displacement led cement to channel through mud which prevent accom-
plishment of zonal isolation and casing support during primary cement job. This impact wors-
ens for long, horizontal well cementing since mud remained can be locked and unable to be
removed even at higher pumped cement volumes. Lowering cement rheology within practical
limits improves cement placement and enhance turbulent flow operations | en |