Page 83 - Intelligent Digital Oil And Gas Fields

54 Intelligent Digital Oil and Gas Fields

Fig. 2.8 shows an example of a pipe flowing three phases with a void gas
fraction e g of 0.50, oil 0.15, and water 0.35. The corresponding gas, oil, and
water volume factor is also shown.
2 The Lockhart-Martinelli parameter (χ) can be calculated from the mass
flow rate or volumetric flow rate of liquid and gas and the density of the
fluids, which is a dimensionless number. The parameter helps to define
the wetness or liquid loading of the gas using the following range: A wet
gas flow has a value of between 0.0 and 0.3, and values above 0.3 are
defined usually as multiphase flows.

ρ
s ffiffiffiffiffiffiffi
Q liq gas
x ¼ (2.6)
Q gas ρ
liq
In summary:

Gas void Gas volume Lockhart-Martinelli
Phase factor (e g ) factor (GVF) parameter (χ)

Gas single phase >0.7 >0.9 <0.3
(wet gas)
Multiphase flow 0.4–0.69 0.5–0.89 0.31–0.61
Liquid single phase <0.3 <0.5 >0.62

• Intermittent flow (plugging and slugging) occurs when gas flows in slugging
or intermittently (not continuously), and liquid dominates the total void
fraction. Liquids have moderate high velocity and gases have low veloc-
ity. This is a more frequent flow before separation, it normally occurs in a
black oil system with low GOR.
• Bubble flow occurs at a high liquid velocity and is characterized by gas
bubbles floating over a continuous liquid phase. Here the multiphase
flowmeter (MPFM) works with high accuracy.
• Annular flow occurs at high gas and liquid velocities and with a significant
viscosity contrast between the gas and the liquid (μ g /μ liq ). The gas flows
in the central core of the pipe and liquid flows as a film on pipe walls.
• Mistflowoccurswhenthegasvelocityandthedensityincrease,andthenthe
liquid becomes entrained as droplets in the gas flow. A portion of the liquid
travels on the pipe’s wall, and another portion flows suspended by the gas
flow. This flow is predominant in gas condensate and volatile oil systems.