Page 314 - Intelligent Digital Oil And Gas Fields

262 Intelligent Digital Oil and Gas Fields

3
ρ is the fluid density of the mixture phases (lbm/ft ),
0.5
Cv is the flow coefficient in USgal/(min psi ) (which is measured in the lab
of the service provider),
3
ρ wstd is the water density measured at standard condition in lbm/ft , and
γ is the liquid gradient of the mixed fluids.
The Cv performance is represented by a choke valve opening versus flow
rate table determined at lab condition using compressible fluid at high
temperature and pressure. Fig. 7.10 shows a pressure drop versus oil flow
rate delivered by an ICV flowing oil fluid at 2600psi and 200°F in tubing
size of 3–1/2in., oil API of 30 and gas gravity of 0.81. Cv values are observed
in each position (Pos).

7.6.1 Single-Zone Control Analysis Using an ICV

The results of the Perkins equation at different pressure drops across the
valve were superimposed on the IPR and VLP plot showed in Fig. 7.11.
The values of the pressure differentials may be considered at discrete flow
rates as a fraction of the maximum flow rate, such as 20%, 40%, 60%,
etc., and the operating points at the perforation node are represented by
the corresponding points labeled A, B, C, D, E, and F. The number of dis-
crete positions corresponds to set positions of the flow control valve.
Konopczynski and Ajayi (2004) referred to these as attenuated IPR curves.

7.6.2 Multiple-Zone Control Analysis Using ICVs
The process for multiple-zone intervals is very similar to the process for a
single zone. However, the main limitation is that the process assumes that
all zones have the same reservoir pressure, fluid composition, and bubble
point. Another important assumption is that the Cv flow coefficient and
devices are equal for all zones. They established two methods to estimate
the pressure across the valve:
• Constant pressure. This method assumes that only the flow from Zone A is
modulated while the production from all other zones is maintained at a
constant rate. To satisfy this constraint, the flowing bottom-hole pressure
must be held at a constant value.
• Independent flow. This method assumes that the fluids flow only from the
zone of interest through tubing and the other zones are shut-in; it is sim-
ilar to the single-zone method.
For this particular example, Konopczynski and Ajayi (2004) useda tubing size
of 5–1/2in. to independently flow in five zones, with IPs that vary between
3.4 and 7 b/d/psi at a surface wellhead pressure of 150psi. Fig. 7.12 (left)