| Summary: | When drilling fluids circulate through the well and during the solids control operations, they are exposed to vibrations and oscillations of different frequencies and amplitudes. The secondary flow structures in oscillatory motion influence the liquid shear rate and rheological characterization of drilling fluids. Hence, oscillations understandably influence the cuttings carrying capacity of the drilling fluids and the solids separation efficiency as well. The majority of pipe flow investigations available in the scientific literature are related to the steady flow. However, more attention should be paid to unsteady flows, since there are many industrial and biological applications in the fields of applied fluid mechanics. As an example, even local geometrical variations and gas kicks in oil-well drilling operations might cause flow instabilities and fluctuations along the pipe trajectory. The problem of shear rate change in time-periodic flows of viscoelastic fluids is relevant in particular for the oil industry, as acknowledged by the research, and also for physiological flows such as blood flow in veins and arteries and the flow of mucus driven by cilia oscillations; hence the interest of the proposed research. This thesis presents a collection of six experimental studies and one numerical study which aims to investigate the effect of zero-mean oscillatory flow on particle settling in shear thinning polymeric non-Newtonian fluids of interest in drilling and maintenance of petroleum wells. In most of the cases, a mixture of water-based polymeric solutions of Polyanionic Cellulose (PAC) and Carboxymethyl Cellulose (CMC) has been employed as the test fluids and in some cases, an individual type of polymer solution has been employed with the viscosifier, Xanthan gum (Xg). The rheological properties of the slightly viscoelastic test fluids have always been characterized in all the sub-studies based on the specific experimental conditions and it is shown that the test fluidsexhibit a shear thinning viscosity in the ...
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