Viscous liquid-gas two-phase flow experiments with liquid viscosity ranging from 1000 – 5000 cP (1.0 – 5.0 Pa.s) and air as the gas phase were compared with the point model simulations obtained from OLGA, a multiphase flow simulator. Flow patterns, pressure gradient, mean liquid holdup and slug frequency were obtained through experimental observations and measurements using high speed video camcorders, differential pressure transducers and Electrical Capacitance Tomography (ECT). Results show that OLGA gave a good prediction of the measured pressure gradient however with decreasing capabilities as liquid viscosity increased. OLGA point model over predicted the slug flow pattern and under predicted the liquid holdup in this study.
The oil and gas industry is increasingly looking towards unconventional resources like heavy oil (defined as petroleum liquid API gravity <22° and viscosity >0.1 Pa.s) to help satisfy world energy demand as conventional reserves are continuously depleted due to several years of production and consumption. The quest for heavy oil production is also fuelled by its ready availability; Meyer and Attanasi (1) writing for the United States Geological Survey (USGS) puts the technically recoverable heavy oil and natural bitumen as equal to reserves of conventional oil (defined as petroleum liquid with API gravity >22° and viscosity <0.1 Pa.s) in known conventional oil accumulations. Viscous oil hydrodynamic characteristics are different from conventional oil (light oil) due mainly to its physical properties. As a result of these significantly different physical properties, heavy oil is more challenging to produce and transport. The major implication of these differences is seen in the design of heavy oil production systems as well as in the implementation of technologies which were mostly developed on the basis of hydrodynamics characteristics of light oil.
Effect of liquid viscosity on two-phase oil-gas flow have been investigated by some researchers and reported in literature. Gockal et al. (2), experimentally studied the effect of liquid viscosity of up to 0.589 Pa.s on oil-gas two-phase flow, they concluded that existing models were insufficient in predicting the flow variables observed and that the intermittent flow region was enhanced with increased viscosity. Marquez and Trujillo (3), Matsubara and Naito (4), Zhao et al. (5) and Folletti et al. (6) have reported increased intermittent flow region in their studies.