Cement Displacement Efficiency in Smooth and Rough Pipes - An Experimental and Theoretical Investigation
Abstract
Researches in the industry have always ascertained that mud channels affect the two principalobjectives 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-slipboundary condition, is among the reasons behind mud channeling. This study aims at cementdisplacement efficiency based on investigation of operational parameters and conditions thatcontrol 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 forlaminar and turbulent flow of Newtonian, Bingham plastic, and Power-law fluids in a horizontalpipe. Eulerian method of flow description is employed to locate fluid interface through timealong a radially discretized control volumes.The respective effect of viscosity and flow rate on displacement efficiency was studied bothunder turbulent and laminar flow conditions. Increase in flowrate followed by surpass of criticalReynolds number brings robust displacement efficiency. Around 15% theoretical displacementefficiency superiority of turbulent regime over laminar flow was recorded at the tested conditionsfor both Newtonian and Power-law fluids. After turbulent flow is reached, an increase of flowrate brought slight decrease of efficiency for Bingham and Power-law fluids while efficiencyof 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 bringshigher displacement efficiency when critical Reynolds number is exceeded. However, decreaseof apparent viscosity during laminar flow of Bingham fluids resulted in decrease of efficiencyas 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 turbulentflow. 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 beremoved even at higher pumped cement volumes. Lowering cement rheology within practicallimits improves cement placement and enhance turbulent flow operations