Artificial lift

Diving Into Multiphase Flow

Getting more out of gas lift requires understanding how gas injections interact with the oil, water, and gas flowing up the well—in other words, multiphase flow. Some papers are listed to get you started.

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Editor’s Note: Read Now Is the Time for Gas Lift To Live Up to Its Potential.” The way gas injection is used to lift oil and water to the surface needs to change because better control and data may mean more production. At a time when engineers are managing so many wells, they need help from machines.

The short answer for how gas lift works is: It reduces the density of the fluid flowing in the well, making it easier to lift.

Making a fluid more buoyant is a plus. But engineers looking for ways to maximize the production from lift describe a more complicated picture when asked how injected gas interacts with a stream of oil, water, and produced gas.

For gas-lift experts such Anand Nagoo, a consultant whose firm is called Nagoo & Associates, understanding these multiphase interactions is the key to finding ways to maximize the efficiency of gas-lift injections.

There is a large body of work for lift engineers to draw on, though most of it was done by researchers outside the upstream oil business. Those papers describe how flow can be affected by the properties of the fluids, the pipe, and the changing size of the gas bubbles in the flow.

Nagoo, who is also an associate editor for the peer-reviewed journal SPE Productions & Operations and a technical paper reviewer, recommended a list of papers for those looking for a deeper understanding of how gas lift works.

A review of various forms of bubbly flow associated with continuous gas lift and how they affect lift performance.

Guet, S. and Ooms, G. 2006. Fluid Mechanical Aspects of the Gas-Lift Technique. Annual Review of Fluid Mechanics.

An introduction to averaged multiphase flow theory for students, scientists, and practicing engineers.

Ishii, M. and Hibiki, T. Thermo-Fluid Dynamics of Two-Phase Flow. Springer (2006).

Classic experiments reveal the fundamentals of upward gas/liquid bubbly flows. Using observations from advanced instrumentation, these papers describe cross-sectional bubbly flow profiles and bubble size distributions observed in tests.

Liu, T.J. and Bankoff, S.G. 1993. Structure of Air-Water Bubbly Flow in a Vertical Pipe–I. Liquid Mean Velocity and Turbulence Measurements. International Journal of Heat and Mass Transfer.

Liu, T.J. and Bankoff, S.G. 1993. Structure of Air-Water Bubbly Flow in a Vertical Pipe–II. Void Fraction, Bubble Velocity and Bubble Size Distribution. International Journal of Heat and Mass Transfer.

Advances in Gas-Liquid Flows. 1990. Presented at the Winter Annual Meeting of the American Society of Mechanical Engineers, Dallas, Texas.

A modeling-focused paper offers a deep look at the fundamental mechanisms governing bubble breakup and coalescence, mostly in wells with low gas/liquid ratios.

Nguyen, V.T.; Song, C-H.; Bae, B-U.; and Euh, D-J. 2012. Modeling of Bubble Coalescence and Break-Up Considering Turbulent Suppression Phenomena in Bubbly Two-Phase Flow. International Journal of Heat and Mass Transfer.

A review of bubbly flow focuses on high gas-to-liquid wells where bubbles transition to slug, churn-turbulent, and annular flow, which all reduce lift.

Montoya, G.; Lucas, D.; Baglietto, E.; and Liao, Y. 2016. A Review on Mechanisms and Models for the Churn-Turbulent Flow Regime. Chemical Engineering Science.