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Due to the potential hazard of deepwater oil exploration, the Brazilian industry has an ever-increasing concern for reliability during hydrocarbon production. A major source of concern is mechanical failure in devices, such as safety valves, which can fail without warning, putting both the operation and the environment at risk. A possible reason for malfunction and failure could be the permanent occurrence of vibrations induced by internal two-phase flow during the extraction of fluids from the well. An experimental campaign is proposed to better understand these phenomena. Twenty two-phase flow conditions were tested, with superficial velocities ranging from 0.1 m/s to 2.0 m/s for water, and 0.33 m/s to 7.47 m/s for compressed air. The experiments were carried out in a restricted pipe and a pipe without any restriction to evaluate and compare the vibrations produced by two-phase flow (2-FIV). Three accelerometers positioned downstream of the restriction were used to collect vibrational amplitude spectral density data, 2-D acceleration magnitudes, and RMS values of acceleration. Among the main findings are the roles played by the gas volumetric fraction and the mixture velocity, which strongly influence the vibrational amplitude of both tubes, and the observation that the gas phase is the main responsible for vibrational amplitudes at low frequencies, while the liquid phase acts mainly at high frequencies. Furthermore, the flow pattern is also considered a key feature in determining the vibration level, as 20- and 12-fold increments have been observed for the same volumetric fraction when comparing elongated bubbles and severe slug patterns. Finally, it was demonstrated that the presence of an internal restriction strongly influences the structural response. • The presence of an internal restriction affects a pipe's dynamic response significantly. • Large changes in vibratory response are found between single-phase and two-phase flow. • It is suggested that the gas phase is responsible for the vibration amplitudes at low frequencies. • It is suggested that the liquid phase is responsible for the vibration amplitudes at high frequencies. • Two-phase flow parameters directly influence the structural response to vibration. [ABSTRACT FROM AUTHOR]

• A restriction affects the pressure of a two-phase flow, representing large differences compared to an unrestricted pipe. • Downstream of the restriction there is an increase in the void fraction due to the breaking of bubbles and loss of pressure. • Upstream of the restriction there is an increase in the length and velocity of the liquid slugs due to bubble coalescence. • 14 models from the literature, between pressure gradient, void fraction, and frequency of passage of liquid slugs are used to compare with experimental data. Subsurface safety valves play an important role in the hydrocarbon production process. The Brazilian industry is suffering significant losses due to the reduction of the useful life of this device, not to mention the risks associated with the operation and the environment. One possible reason for the failure of the subsurface safety valve's reliability prediction may be the occurrence of two-phase flow in the well. For this reason, a set of twenty horizontal two-phase flow experiments was carefully designed to evaluate the influence of a simplified internal reduction in a steel pipe. Superficial velocities were considered in the range of 0.1 m/s and 2.0 m/s for water and, 0.33 m/s and 7.47 m/s for compressed air. The experiments were carried out in 2″-i.d. and 2-m-long steel pipes, being a tube with restriction and another without restriction. Both tubes have an upstream development length of 126 pipe diameters. Gamma-ray densitometry and a differential pressure transducer were used to measure void fraction and pressure drop, and a visualization window was used to observe the flow patterns. Among the main findings are the effects of void fraction and mixture velocity on pressure gradient, with different impacts on the restricted pipe (RP) compared to the unrestricted pipe (UP). The presence of the restriction generated significant changes in the upstream flow: the lengths of the liquid slugs were increased, appeased by the increase in local pressure necessary to overcome the resistance produced by the restriction. Downstream, the change was reflected in the rise of void fraction and decrease of slip ratio between the phases. [ABSTRACT FROM AUTHOR]