Effect of the water fraction on the gas-lift efficiency applied in the artificial lift of heavy oil

• Grant number: 12/04557-7
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: June 01, 2012
• End date: May 31, 2013
• Field of knowledge: Engineering - Mechanical Engineering - Transport Phenomena
• Principal Investigator: Oscar Mauricio Hernandez Rodriguez
• Grantee: Alex Roger Almeida Colmanetti
• Host Institution: Escola de Engenharia de São Carlos (EESC). Universidade de São Paulo (USP). São Carlos , SP, Brazil

Abstract

Most offshore oil wells exploited in Brazil use the gas-lift artificial lift technique. More importantly, it is predicted an intensive use of gas-lift in the pre-salt wells, under extreme pressures and operating conditions that have not been yet completely understood. The effect of injecting gas into a flow in a vertical pipe is the decrease of the gravitational component of the total pressure gradient, which is the principle behind the gas-lift technique. The total pressure gradient is reduced in air-water or low-viscosity oil and gas flow since these are dominated by gravity. However, in the flow of viscous oil, the frictional component can be of the same magnitude as the gravitational component, if not preponderant. Therefore, there must exist a fluid viscosity limit for each specific flow condition above which the gas-lift technique becomes inefficient. Another issue is the three-phase oil-water-gas flow. In the region of phase inversion, gas injection tends to significantly increase the frictional pressure gradient, making again the gas-lift technique inefficient. This project aims at assessing these issues by conducting laboratory tests using mixtures of oil of moderate viscosity (300 mPa.s) and water. The gains due to gas injection will be quantified through pressure-gradient reduction factors. The gains will be simulated via a phenomenological model as a function of the effective viscosity of the oil-water mixture. The ultimate goal is to verify the reliability of model predictions by comparison with experimental data collected in the multiphase-flow facilities of NETeF. (AU)