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Experimental study of displacement of viscoplastic fluids in eccentric annulus Foolad, Yasaman


This thesis presents a series of targeted, practical experiments focused on the displacement of viscoplastic fluids with various Newtonian and non-Newtonian fluids in a horizontal, eccentric annuli in laminar, turbulent and transitional flow regimes. The motivation of this study originates from primary cementing of horizontal oil and gas wells. During primary cementing, a sequence of fluids are pumped down through a metal casing and up through an annular region between the casing and a wellbore. Commonly, a low-viscosity, low-density preflush starts the sequence, followed by a denser and more viscous spacer fluid. Eventually, cement slurries are pumped and placed in the annular region to provide hydraulic isolation and mechanical stability to the well. The eccentricity of the annular region, as well as the viscoplastic nature of the fluids involved, might result in several fluid-related defects, such as residual mud channeling that allow the well to leak later. There are existing 2D and 3D models of primary cementing developed for various flow regimes, including the laminar model of Bittleston et al. and the turbulent and mixed model of Maleki & Frigaard. These modelling approaches provide us with valuable information. However, there is an undeniable demand for experimental studies to validate the outcomes of such models. The main objective of our experiments was to experimentally gain insight into the role of flow regime, specifically turbulence, in fluid-fluid displacements that take place in primary cementing. The experiments performed in this study can be classified in three sets, including turbulent displacement flow of viscoplastic fluids in eccentric annulus, as well as comparative studies of laminar-turbulent displacement in eccentric annulus under imposed flow rate and imposed pressure drop conditions. The outcome of this experimental analysis allows us to understand the role of flow regime in the process of cementing in more depth. In particular, we show that some simple statements that are widely employed in industry do not necessarily apply at all design scenarios. Instead, detailed study of the fluids involved and specifying operating flow conditions in accordance to specific features of wells can yield improved displacement quality and reduced cementing complications.

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