BR 
EN 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.
Mês: julho 2023
Flow Visualization In The Impeller And Diffuser Of A Centrifugal Pump Using Time-Resolved Particle Image Velocimetry
The present paper describes an experimental study on the flow dynamics within a centrifugal pump impeller. A transparent pump prototype made of acrylic parts was firstly developed for flow visualization purposes. Then, single-phase flow experiments were conducted in different impeller rotational speeds and water flow rates. A time-resolved particle image velocimetry (TR-PIV) system was used as the flow visualization method. As a result, velocity fields were obtained in the whole impeller. They reveal that the flow behaviour is dependent on the pump operational condition. When the pump works at the best efficiency point (BEP), the flow is uniform and the streamlines follow the blade curvature. However, when the machine works at off-design conditions, the flow becomes complex, with the presence of turbulent structures which cause a reduction in the pump performance. This type of result may be useful to validate numerical simulations and support the proposition of new mathematical models, new impeller geometries, among other applications.
Visualization Of Oil-Water Emulsion Formation In A Centrifugal Pump Stage
Electrical submersible pumps are assembled in oil wells to act as artificial lift methods. When water is present in the reservoir, oil-water emulsions are formed in the pump. These two-phase mixtures affect the performance and promote instabilities that lead the machine to operate inefficiently and fail prematurely. Therefore, this paper aims to investigate the formation of emulsions and behavior of mineral oil drops in a transparent centrifugal pump through a flow visualization approach. Shut-off, best efficiency point, and open-flow condi tions are investigated at three impeller rotational speeds with high-speed imaging and particle image velocimetry. As the oil fraction increases, large drops accumulate in the impeller channels, while some escape to the volute and circulate until the water flow carries them out of the pump stage. Regions with vortices and water recirculation explain the accumulation of oil drops in the impeller and reduced pump performance at low water flow rates. Intense velocity fluctuations at the impeller and impeller-volute boundary indicate the main causes for oil drop rotation, deformation, and fragmentation at high water flow rates. The new findings can be used to improve models and numerical simulations for pumps operating with multiphase flows and help the creation of new pump designs.
Evaluation of the effect of wax concentration in crude oils on the dimensionless temperature plateau
One of the main challenges regarding crude oil production under low temperatures in deep seas concerns
the wax deposition in pipelines. This issue presents a high level of complexity and the governing mechanism
is still under investigation. Considering the deposition phenomenon and seeking to improve the knowledge
about the governing mechanism and the main variables influencing the final behavior, the present work
analyzes how different oil compositions and mixtures, under different flow conditions, impact the deposit wax
thickness. It also compares the dimensionless temperature for different wax concentrations, which allows to
evaluate the behavior of the temperature gradient, and verifies the behavior of the plateau under different
Reynolds numbers. Finally, the mechanism proposed in this work is compared with the behavior proposed by
the main governance mechanisms discussed in the literature in the last decades.
Experimental Investigation on Velocity Fields, Vorticity, and Turbulence within the Stage of an Electrical Submersible Pump (ESP)
This paper presents an experimental study on the flow dynamics within an Electrical Submersible Pump (ESP) stage. An ESP prototype with transparent impeller and diffuser was designed and manufactured to allow flow visualization, which was achieved by using a Time-Resolved Particle Image Velocimetry (TR-PIV) system. Single-phase water flow tests were conducted in various flow rates corresponding to percentages of the Best Efficiency Point (BEP). The average velocity fields, vorticity contours, and turbulent kinetic energy values obtained in the whole impeller reveal that the flow behaviour is very dependent on the ESP operational condition. Energy losses due to turbulence are lower when the pump works at the BEP. But when the device operates at off-design conditions, the flow becomes complex, with high vorticity and turbulence which cause a reduction in the performance. This type of investigation may be useful to validate numerical simulations, support the proposition of mathematical models, or help create improved impeller designs.
Understanding ESP Performance Under High Viscous Application and Emulsion Production
Although being widely used as an artificial lift method for heavy oil field developments, Electrical Submersible Pump (ESP) system performance in high viscous applications is not fully understood. A miscomprehension of challenges and equipment performance in such conditions might lead to operation inefficiencies and equipment failures. This paper presents results of single-phase and multiphase tests performed by University of Campinas (UNICAMP). It also presents operation data, lessons learnt, and failure examples gathered over 10 years of ESP operation in Peregrino field which is a heavy oil, high viscous oilfield offshore Brazil operated by Equinor.
Affinity laws commonly used for ESP simulations don’t hold true for high viscosity applications. Hydraulic performance of centrifugal pumps is affected by fluid parameters like viscosity and density; operation parameters such as flow rate and rotational speed; and specific stage design characteristics. To determine degradation in head and efficiency as well as power requirement increase in viscous applications, Equinor performs one-phase high viscosity flow loop test to qualify each stage type prior to deployment in Peregrino field.
For the qualification of ESPs, single phase qualification tests are performed using mineral oil with viscosities specifically chosen to cover the viscosity range of the specific field. Each stage type is qualified using a prototype with reduced number of stages due to flow loop limitations. Qualification tests for the Peregrino field confirmed that affinity laws are not accurate for high viscous applications and provided important insights regarding pump performance that are used in equipment specification and system surveillance.
The UNICAMP research team has designed and performed multiphase flow tests to evaluate emulsion formation inside centrifugal pump stages and effective viscosity behavior. Phase inversion phenomenon investigation was also included in studies. Studies performed using a prototype stage allowed visualization and evaluation of oil drops dynamics inside the impeller in different rotational speeds. Two phase flow loop tests investigated the shear forces influence in effective viscosity inside pump stages and downstream pump discharge. Phase inversion phenomenon was also a point of great interest during the studies. Data gathered during lab tests was used to evaluate accuracy of mathematical models existing in the literature when a centrifugal pump is added to the system. Hysteresis effect associated to catastrophic phase inversion (CPI) was confirmed and replicated during flow loop tests. Such behavior can be related with operation parameters instabilities and equipment failures noticed in actual application in Peregrino field which are also presented in this paper.
Comparing WAG-CO 2 injection with continuous water and gas injection in separate wells for the development and management of a CO2-rich light oil fractured carbonate reservoir subject to full gas recycling
Many projects in the Brazilian pre-salt assume the use of water alternating gas (WAG-CO2) injection as an ecologically safe carbon storage strategy, with improved hydrocarbon recovery. However, studies that compare these advantages with a simpler management plan are not common. The objective of this work is to compare WAG-CO2 injection with continuous injection of water and gas (CIWG) rich in CO2 in separate wells for the development and management of a light-oil fractured carbonate reservoir subject to full gas recycling. We employed the UNISIM-II benchmark model, a naturally fractured carbonate reservoir with Brazilian pre-salt characteristics, which enables an application in controlled environment where the reference response is known (UNISIM-II-R). We used a model-based decision analysis for production strategy selection, hierarchical optimization of the decision variables and algorithms to maximize the objective function. Representative models (RM) are selected from the ensemble of models and used to incorporate the effects of geological, reservoir, and operational uncertainties into the optimization process. The net present value is the objective function during the nominal optimization of candidate strategies of each RM and the expected monetary value and risk analysis are considered to select the final production strategy considering uncertainties. The risk analysis was quantified based on downside risk and upside potential relation to a benchmark return. We optimized two alternative development plans (one considering WAG-CO2 injection and the other continuous injection of water and gas in separate wells) and compared their performance indicators and decision variables, including design variables (number, type and placement of well, and size of production facilities) and life-cycle control rules (management of equipment over time). We then applied a cross-simulation, where the best strategy optimized for one recovery method was applied to the other and the injection strategy was optimized again. We were therefore able to assess the need to pre-define the recovery method before defining design variables to validate the flexibility of each strategy for possible future changes in the recovery mechanism. Finally, we repeated the study for different reservoir scenarios to compare the alternatives considering typical uncertainties of the Brazilian pre-salt and validated the final strategies in the reference model to quantify the real value in decision making. The strategies reached a full gas recycling in both recovery methods and allowed a comparison of their advantages and disadvantages. The operations of WAG-CO2 injection can be more complex and the equipment more expensive. The novelty of this work is the consideration of continuous injection of water and gas in separate wells as a simpler alternative to the development and management of pre-salt oil fields, since this method may also meet operators’ and environmental demands, bearing simpler operating challenges and promoting good recovery and profitability.
A coupled PIV/PTV technique for the dispersed oil-water two-phase flows within a centrifugal pump impeller
The current work presents a framework for the simultaneous characterization of different phases in a dispersed oil-water two-phase flow. The framework is based on the coupling of the PIV and PTV techniques in raw PIV acquisition images. The PIV technique computes the water velocity fields, while the PTV technique calculates the oil drop velocities. Thus, the proposed technique allows the simultaneous measurement of the water phase and dispersed oil drop velocity from the same image. In order to present the advantages of the coupled PIV/PTV technique, the flow within a centrifugal pump impeller is completely analyzed by computing the oil and water phase-ensembled velocities.
Effects of the Random Forests Hyper-Parameters in Surrogate Models for Multi-Objective Combinatorial Optimization: A Case Study using MOEA/D-RFTS
Surrogate models are techniques to approximate the objective functions of expensive optimization problems. Recently, Random Forests have been studied as a surrogate model technique for combinatorial optimization problems. Nonetheless, Random Forests contain several hyper-parameters that are used to control the prediction process. Despite their importance, research on the effects of these hyper-parameters is scarce. Therefore, this paper performs a systematic investigation of the effects of different combinations of values for the Random Forest hyper-parameters on the approximation of well-known multi-objective combinatorial benchmark problems. The results show that the number of samples to consider when building each tree and the minimum number of samples to be at the leaf node are the two most important hyper-parameters in this context.