Page 202 - Petroleum Production Engineering, A Computer-Assisted Approach

Guo, Boyun / Computer Assited Petroleum Production Engg 0750682701_chap13 Final Proof page 198 3.1.2007 9:07pm Compositor Name: SJoearun

13/198 ARTIFICIAL LIFT METHODS
Detailed descriptions of these procedures are given by
Brown (1980). Only the design procedure using constant
surface opening pressure for pressure-operated valves is
illustrated in this section.
Figure 13.18 illustrates a graphical solution procedure
P t of valve spacing using constant surface opening pressure
for pressure-operated valves. The arrows in the figure
depict the sequence of line drawing.
For a continuous-flow gas lift, the analytical solution
A p
procedure is outlined as follows:
P c
1. Starting from a desired wellhead pressure p hf at surface,
compute a flowing tubing-pressure traverse under fully
Small orifice
unloaded condition. This can be done using various two-
phase flow correlations such as the modified Hagedorn–
S t Brown correlation (HagedornBrownCorrelation.xls).
2. Starting from a design wellhead pressure p hf,d ¼ p hf
þ Dp hf,d at surface, where Dp hf can be taken as
0:25p c,s establish a design tubing line meeting the flow-
ing tubing-pressure traverse at tubing shoe. Pressures in
this line, denoted by p td , represent tubing pressure after
A p adjustment for tubing pressure margin. Gradient of this
line is denoted by G fd . Set Dp hf ¼ 0 if tubing pressure
margin is not required.
3. Starting from a desired injection operating pressure p c
at surface, compute a injection operating pressure line.
This can be done using Eq. (13.7) or Eq. (13.9).
P c 4. Starting from p cs Dp cm at surface, where the casing
pressure margin Dp cm can be taken as 50 psi, establish a
Figure 13.16 A sketch of a differential valve. design casing line parallel to the injection operating
pressure line. Pressures in this line, denoted by p cd ,
represent injection pressure after adjustment for casing
c. Design procedure for fluid-operated valves. pressure margin. Set Dp cm ¼ 0 if the casing pressure
d. Design procedure for combination of pressure-closed margin is not required as in the case of using the
fluid-opened values. universal design method.

P d P d

P d
A b A b
A b

P P P
P t c P c c P c c

P t P t
Both bellows and pilot Bellows valve open and pilot Both bellows and pilot
valves closed valve closed valves open
Figure 13.17 A sketch of combination valve.