Determinação do coeficiente de descarga em ejetores de brocas de perfuração de poços de petróleo e gás

Abstract

The difficult to determine the discharge coefficient of drilling bits ejectors of oil and gas wells is a problem present in the petroleum industry. Improving the drilling process, such as increasing the rate of penetration and the cleaning efficiency of cuttings, can be related to precise calculate the discharge coefficient under specified conditions. Since unknowing this design parameter can result in unnecessary spending, the present study aimed to evaluate the influence of factors that affect the discharge coefficient in flows through an axisymmetric abrupt contraction. The software Ansys® PolyFlow was used for the numerical simulations of Newtonian, shear-thinning and Herschel-Bulkley fluids. It was compared different aspect ratios and Reynolds number assuming laminar, isothermal, incompressible and steady flow. The fields of pressure, velocity and shear stress obtained from the simulations allowed obtaining curves showing the behavior of the discharge coefficient as a function of rheological, geometric and kinematic parameters. The results achieved were compared with experimental and theoretical values provided by the literature and demonstrate excellent agreement. In general, the discharge coefficient revealed to be indirectly proportional to the aspect ratio and directly proportional to the Reynolds number. The viscoplastic fluid proved to be the most sensitive to flow conditions changes and showed the highest discharge coefficient values.