Page 198 - Petroleum Production Engineering, A Computer-Assisted Approach

Guo, Boyun / Computer Assited Petroleum Production Engg 0750682701_chap13 Final Proof page 194 3.1.2007 9:07pm Compositor Name: SJoearun

13/194 ARTIFICIAL LIFT METHODS
P
(a) Initial condition tbg
All valves G s
open

P tbg
(b) Gas enters the
first valve
All valves
open G f G s

P tbg
(c) Gas enters the
second valve
The first
valve
begins to
G
close f

(d) Gas enters the Valves P tbg
last valve closed

Valve
begins G f
to close

P tbg
(e) Unloaded
condition
All
unloading
valves
closed
G f

Figure 13.7 Well unloading sequence.
in continuous flow installations but is particularly important
in intermittent gas lift installations where unbalanced
valves are used. The spread controls the minimum amount
of gas used for each cycle. As the spread increases, the
amount of gas injected during the cycle increases.
Gas passage of unbalanced valves are tubing-pressure
dependent due to partial travel of the valve stem. Figure
13.11 illustrates flow characteristics of unbalanced valves.
q g, scf/day
13.5.2.1.2 Balanced Pressure Valve Figure 13.12
depicts a balanced pressure valve. Tubing pressure does
not influence valve status when in the closed or open
condition. The valve opens and closes at the same
pressure—dome pressure. Balanced pressure valves act as Critical
expanding orifice regulators, opening to pass any amount flow ratio
of gas injected from the surface and partial closing to
control the lower gas flow rate. P
Tubing Pressure, (psi) c
13.5.2.1.3 Pilot Valve Figure 13.13 shows a sketch of a
pilot valve used for intermittent gas lift where a large port Figure 13.8 Flow characteristics of orifice-type valves.