Session: 11-07-01 Petroleum Production: Offshore Systems and Subsea Operations

Submission Number: 175678

Effective Viscosity of Emulsions Within Electrical Submersible Pumps 

It is well-documented in the current literature that the performance of centrifugal pumps is significantly impacted by the viscosity of the working fluids. While predictive models for pump performance with viscous fluids have been extensively proposed, they typically assume the fluid is Newtonian. In the oil and gas industry, it is common for water to be present among the produced fluids. The arrangement of the two immiscible liquid phases, water and oil, can take the form of a water-in-oil dispersion. These colloidal dispersions are commonly called emulsions and can be stabilized by crude oil components such as asphaltenes and resins. This stability causes the coalescence of water droplets to occur at a considerably slower rate, reducing the average droplet size. Consequently, the viscosity of water-in-oil emulsions can reach very high magnitudes and exhibit strong non-Newtonian, shear-thinning behavior under simple shear.

Due to the variable nature of emulsion viscosity, which depends on the applied strain rate, the models available in the literature cannot accurately predict the performance of centrifugal pumps used in petroleum production. In this work, a recent model developed for various centrifugal pump geometries (ranging from radial to mixed-flow) operating with viscous fluids was utilized as a tool to predict the effective viscosity of stable water-in-oil emulsions (mineral oil SPAN 80) under different operational conditions in a radial pump and a mixed-flow pump. Since the model uses fluid viscosity as an input parameter, the viscosity that yielded the best fit with experimental data was determined based on the head versus flow rate performance curve. This process was repeated across water-cuts ranging from 16% to 31% and temperatures between 30°C and 45°C, using mineral oil (SPAN 80) and tap water. The pumps speeds were 2400, 3000 and 3500 rpm.

The results indicated that it is not possible to estimate the entire operating range using a single viscosity value. Points at low flow rates showed worse performance than predicted (higher viscosity), while points at high flow rates demonstrated better performance (lower viscosity), which is consistent with the shear-thinning behavior of the emulsions. Based on these findings, an analysis of the effective viscosity for each point on the performance curve was proposed. This analysis resulted in plots of the effective viscosity experienced by the centrifugal pumps as a function of the flow rate for each of the tested pumps. It was noted that the pump geometry has an impact on the effective viscosity, even under the same operating conditions (rotational speed, temperature, and water concentration). The results demonstrate the importance of considering the effect of emulsion viscosity during the design of centrifugal pumps, as well as the impact of shear-thinning behavior at different operating points, which has a variable effect on the expected pump performance.

Presenting Author: Matheus Garros School of Mechanical Engineering, University of Campinas

Presenting Author Biography: Energy Engineer, MSc. degree in Petroleum Sciences and Engineering at the School of Mechanical Engineering of the University of Campinas. PhD student at the Center for Energy and Petroleum Studies, in the areas of multiphase-flow, electrical submersible pumps and non-Newtonian fluids.

Authors:

Matheus Garros School of Mechanical Engineering, University of Campinas
William Monte Verde Center for Energy and Petroleum Studies, University of Campinas
Julio Johner Center for Energy and Petroleum Studies, University of Campinas
Andrey Pulido School of Mechanical Engineering, University of Campinas
Natan Bulgarelli Center for Energy and Petroleum Studies, University of Campinas
Marcelo Castro Department of Energy, School of Mechanical Engineering, University of Campinas