Tag: Phase inversion

Phase inversion identification in Electrical Submersible Pumps using mechanical vibrations

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Electric Submersible Pumps (ESPs) are multistage centrifugal pumps used in the artificial lift and transport of multiphase fluid mixtures. The flow regime is a liquid–liquid flow when the fluids correspond to two non-miscible fluids. Liquid–liquid flow is a mixture with a continuous and dispersed phase. As the amount of fluid in the dispersed phase increases, the dispersed phase suddenly becomes continuous and vice-versa. This transition phenomenon is called phase inversion. The flow regimes in oil–water mixtures are oil-in-water (o/w) and water-in-oil (w/o) flow regimes. This work demonstrates a correlation between the flow regime and the flow-induced vibration (FIV) in ESP operating with an oil–water mixture. This research proposes a novelty method to flow regime identification based on the Root Mean Square (RMS) of the vibration acceleration of the Fast Fourier Transform (FFT) signal.

The experimental setup consists of an 8-stage Electrical Submersible Pump (ESP) and a vibration acquisition system with six accelerometers uniformly distributed along the ESP. The experimental procedure consists of changing the water cut (percentage of water) from the oil flow regime to the water flow regime, maintaining stable ESP rotational speed, the total flow rate, and the oil viscosity. For each water cut, mechanical vibration is collected. The operational conditions consider 30, 40, and 50 Hz rotational speeds and viscosities between 70 and 210 cP.

Frequency domain analysis involves studying FFT between 0 and 5000 Hz, considering different water cuts and frequency ranges. Statistical features – mean, variance, geometric mean harmonic mean, and RMS – were extracted from the FFT for each frequency range. Results showed a strong correlation between the RMS of FFT and the phase inversion phenomena considering the rotational speed. A logistic regression model was employed to establish a transition boundary between oil-in-water and water-in-oil using 10% of the data. The model successfully separated at least 95.67% of the remaining data in the least favorable scenario.

Experimental Investigation Of The Shear Effect On Oil-Water Emulsion Flow In Pipelines

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Emulsion flows have been a severe flow assurance issue, mainly in mature oil fields. Its formation occurs due to shear on oil-water flows caused by artificial lift methods, such as Electrical Submersible Pumps (ESP), and/or valves. The shear rate has an important role in emulsion flow behavior related to its relative viscosity and phase inversion. Therefore, this work presented an experimental investigation of the shear effect on three emulsion systems flowing in a pipeline. The shear element used was a combination of an 8-stage ESP and a glob valve. The emulsion systems analyzed were unstable emulsion and stable emulsion with and without a demulsifier. The experimental investigation was carried out for two ESP rotational speeds, 2400 and 3500 rpm, and one total volumetric flow rate, varying the water cut. From this study, it was observed that phase inversion occurred with increasing shear. Moreover, the effective viscosity was the same regardless of the surfactant presence for the three emulsion systems tested.

Experimental investigation on the performance of Electrical Submersible Pump (ESP) operating with unstable water/oil emulsions

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Electrical Submersible Pump (ESP) is one of the most commonly used artificial lift methods in petroleum production, due to its capacity to operate in several conditions with two or three-phase flows. When the ESP operates with emulsion flow, its performance is degraded, and operational instabilities occur. Therefore, this paper aims to carefully investigate phase inversion and to present, by the first time, the  ffective viscosity of unstable mineral oil/water emulsions, both within the ESP. The first part of this work analyzes the phase inversion phenomenon for two oil types in three viscosities, five ESP rotational speeds, and three mixture flow rates. Logistic functions were fitted using the dimensionless head as a water cut function to determine the phase inversion within the ESP. The continuous phase inversion model, developed for emulsion pipe flow, did not present a satisfactory agreement to flow conditions tested. An indirect method to determine the emulsion effective viscosity within the ESP was proposed, which was obtained from the water/oil emulsion performance curves. The viscous performance data were used to determine the geometric coefficients of a dimensionless head empirical model for the tested ESP. Thus, the calculated values were compared with the effective viscosity obtained with oil and water emulsions, as well as the ESP performance, operating with emulsion and oil, which provides similar values for low rotational speeds. The different behavior of the effective viscosity between the pipeline flow and within the ESP was observed for water-in-oil emulsions and may be related to the high centrifugal field in the ESP.

 

Experimental Study of Phase Inversion Phenomena in Electrical Submersible Pumps Under Oil/Water Flow

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Despite the common presence of water in oil production, just recently, the scientific community has devoted efforts to studying the influence of emulsion phenomena effects related to oil production using pumps. In the context of this study of phase inversion phenomena, the influence of viscosities and rotational speeds in electrical submersible pumps (ESPs) are evaluated as part of this effort. This study is aimed at investigating the influence of viscosity in phase inversion phenomena. An eight-stage ESP was tested with three different rotational speeds and two different oil viscosities for the best efficiency point (BEP) flow rates. Initially, the total flow rate was obtained in relation to BEP using ESP performance curves for pure oil at 52 cP and 298 cP and rotational speeds of 800 rpm, 1200 rpm, and 2400 rpm. The total flow rate was kept constant and the water cut was increased from 0 to 100%. The inversion phase phenomenon was detected by performance improvement when the water cut increased. The factors analyzed were the head and efficiency of the ESP as a function of the water cut. The phase inversion experimental data obtained in this study were compared with literature models for horizontal pipes. The results of this comparison presented satisfactory agreement. The phase inversion phenomena occur in all eight stages at the same time. Hysteresis was observed in ESPs for oil viscosity of 52 cP and rotating speed of 800 rpm and 1200 rpm.