Estudo experimental e de simulação por CFD de escoamentos em seções anulares com excentricidade variável e obstrução parcial da coluna

Abstract

In this thesis are presented experimental measurements of pressure drop and profiles of velocity and pressure gradient simulated via CFD of non-Newtonian fluids in annular ducts concentric/eccentric, with/without rotation of the inner tube, for cases with/without partial obstruction of the annular region. Annular fluid flow is a relevant subject for many industrial applications, especially for the oil and gas industry. It is very important to know the fluid dynamics of the drilling fluid, to assure a proper cleaning of the well and to reduce the effective costs of the operation.In directional drilling often the annulus is eccentric as a result of the column weight, and due to drill bit fluctuations, the eccentricity may vary along the length of the well. Furthermore, by the gravity effect there will be a strong tendency for the solids to accumulate in the bottom of the well, forming a bed of settled cuttings that partially obstructs the flow, which can hinders and even interrupt the drilling operation. For this reason it is important to study the effect of the overlap of these two factors (eccentricity and obstruction) in the flow, which has not been addressed in the literature. Thus, a partnership formed between PETROBRAS and FEQUI/UFU research group allowed the development of this work. A experimental design was used to the acquisition of data regarding hydrodynamic losses in horizontal sections with partial obstruction of 6 mm considering the eccentricity (0, 0.23 and 0.46), flow rate (3, 6 and 9 m3/h), Xanthan Gum concentration (0.1, 0.3 and 0.5%) and rotation of the inner cylinder (0, 200 and 400 rpm). Numerical simulations conducted by using the software FLUENT® 14.0 for periodic sections with different eccentricities (0, 0.23 and 0.46) and obstruction heights (0, 6 and 12 mm) allowed evaluating the influence of operating variables (flow rate of 3 and 9 m3/h and rotations of 0 and 400 rpm) and rheology of the fluid (0.1 and 0.5%) on the flow (axial and tangential velocities profiles and pressure drop data). The injection of particles allowed visualization and dimensioning of the helical path of the same in the annular, which were compared with streamlines simulated by FLUENT®. Comparisons between numerical calculations and literature data indicated, in general, a very good agreement. The results reported on helical flow in annular partially obstructed are a novelty in literature and allow a better understanding of the complex phenomena that may occur in drilling of horizontal and inclined wells.