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A wellhead choke controls the surface pressure and production rate from a well. Chokes usually are selected so that fluctuations in the line pressure downstream of the choke have no effect on the production rate. This requires that flow through the choke be at critical flow conditions. Under critical flow conditions, the flow rate is a function of the upstream or tubing pressure only. For this condition to occur, the downstream pressure must be approximately 0.55 or less of the tubing pressure.  
A wellhead choke controls the surface pressure and production rate from a well. Chokes usually are selected so that fluctuations in the line pressure downstream of the choke have no effect on the production rate. This requires that flow through the choke be at critical flow conditions. Under critical flow conditions, the flow rate is a function of the upstream or tubing pressure only. For this condition to occur, the downstream pressure must be approximately 0.55 or less of the tubing pressure.


==Single-phase gas flow==
== Single-phase gas flow ==
For single-phase gas flow, Beggs<ref name="r1" /> presents '''Eq. 1''', which relates the gas production rate through a choke to the wellhead pressure.


[[File:Vol4 page 0026 eq 001.png]]....................(1)
For single-phase gas flow, Beggs<ref name="r1">Beggs, H.D. 1991. Production Optimization Using Nodal Analysis, 123-127. Tulsa, Oklahoma: OGCI Publications.</ref> presents '''Eq. 1''', which relates the gas production rate through a choke to the wellhead pressure.


The pressure ratio, y, is the ratio of the downstream pressure to the wellhead pressure. Under critical flow conditions, the pressure ratio is replaced by the critical pressure ratio, y<sub>c</sub>. The critical pressure ratio is the pressure ratio at which flow becomes critical. This ratio depends on the ratio of the specific heats of the produced gas, as '''Eq. 2''' shows.  
<sup>[[File:Vol4 page 0026 eq 001.png|RTENOTITLE]]</sup>....................(1)


[[File:Vol4 page 0026 eq 002.png]]....................(2)
The pressure ratio, y, is the ratio of the downstream pressure to the wellhead pressure. Under critical flow conditions, the pressure ratio is replaced by the critical pressure ratio, y<sub>c</sub>. The critical pressure ratio is the pressure ratio at which flow becomes critical. This ratio depends on the ratio of the specific heats of the produced gas, as '''Eq. 2''' shows.


==Two-phase critical flow==
[[File:Vol4 page 0026 eq 002.png|RTENOTITLE]]....................(2)
Empirical equations have been developed to estimate the relationship between production rate and wellhead pressure for two-phase critical flow. These correlations can be presented in a form similar to '''Eq. 3'''.  


[[File:Vol4 page 0027 eq 001.png]]....................(3)
== Two-phase critical flow ==


Gilbert<ref name="r2" /> was the first to present such a relationship based on field data collected from the Ten Section field of California. Ros<ref name="r3" /> and Beggs<ref name="r1" /> have also presented relationships that are often used. '''Table 1''' summarizes the parameters for each equation.
Empirical equations have been developed to estimate the relationship between production rate and wellhead pressure for two-phase critical flow. These correlations can be presented in a form similar to '''Eq. 3'''.


[[File:Vol4 page 0027 eq 001.png|RTENOTITLE]]....................(3)


<gallery widths=300px heights=200px>
Gilbert<ref name="r2">Gilbert, W.E. 1954. Flowing and Gas-Lift Well Performanc. Drill. & Prod. Prac., 126-157. Dallas, Texas: API.</ref> was the first to present such a relationship based on field data collected from the Ten Section field of California. Ros<ref name="r3">Ros, N.C.J. 1960. An Analysis of Critical Simultaneous Gas/Liquid Flow Through a Restriction and Its Application to Flowmetering. Applied Scientific Research 9 (Series A): 374.</ref> and Beggs<ref name="r1">Beggs, H.D. 1991. Production Optimization Using Nodal Analysis, 123-127. Tulsa, Oklahoma: OGCI Publications.</ref> have also presented relationships that are often used. '''Table 1''' summarizes the parameters for each equation.
 
<gallery heights="200px" widths="300px">
File:Vol4 Page 027 Image 0002.png|'''Table 1'''
File:Vol4 Page 027 Image 0002.png|'''Table 1'''
</gallery>
</gallery>


==Example==
This example illustrates the use of the multiphase choke equation ('''Eq. 3''') to estimate the flowing wellhead pressure for a given set of well conditions. However, this equation can be used to estimate flow rate or choke diameter. The example well is producing 400 STB/D of oil with a gas-liquid ratio of 800 Scf/STB. Estimate the flowing wellhead pressure for a choke size of 12/64 in. with Gilbert’s choke equation.


==Solution==
Use '''Eq. 3''' and the proper variable from '''Table 1''' to calculate


[[File:Vol4 page 0028 eq 001.png]]
== Example ==
 
This example illustrates the use of the multiphase choke equation ('''Eq. 3''') to estimate the flowing wellhead pressure for a given set of well conditions. However, this equation can be used to estimate flow rate or choke diameter. The example well is producing 400 STB/D of oil with a gas-liquid ratio of 800 Scf/STB. Estimate the flowing wellhead pressure for a choke size of 12/64 in. with Gilbert’s choke equation.
 
== Solution ==
 
Use '''Eq. 3''' and the proper variable from '''Table 1''' to calculate
 
[[File:Vol4 page 0028 eq 001.png|RTENOTITLE]]


For these conditions, the estimated flowing wellhead pressure is 1,405 psia. If the Ros choke equation is used, an estimated flowing wellhead pressure of 1,371 psia is calculated. Each of the relationships provides slightly different estimates of the calculated value.
For these conditions, the estimated flowing wellhead pressure is 1,405 psia. If the Ros choke equation is used, an estimated flowing wellhead pressure of 1,371 psia is calculated. Each of the relationships provides slightly different estimates of the calculated value.
Line 36: Line 40:


{|
{|
|A<sub>1–3</sub>
|=
|coefficient in '''Eq. 3'''
|-
|-
|''C''<sub>''d''</sub>  
| A<sub>1–3</sub>
|=  
| =
|discharge coefficient, dimensionless  
| coefficient in '''Eq. 3'''
|-
| ''C''<sub>''d''</sub>
| =
| discharge coefficient, dimensionless
|-
|-
|''d''  
| ''d''
|=  
| =
|pipe diameter, L, in.  
| pipe diameter, L, in.
|-
|-
|''k''  
| ''k''
|=  
| =
|specific heat capacity ratio, ''C''<sub>''p''</sub>/''C''<sub>''v''</sub> in '''Eqs. 1''' and '''2''', dimensionless  
| specific heat capacity ratio, ''C''<sub>''p''</sub>/''C''<sub>''v''</sub> in '''Eqs. 1''' and '''2''', dimensionless
|-
|-
|''p''<sub>''sc''</sub>  
| ''p''<sub>''sc''</sub>
|=  
| =
|standard pressure, m/Lt<sup>2</sup>, psia  
| standard pressure, m/Lt<sup>2</sup>, psia
|-
|-
|''p''<sub>''wh''</sub>  
| ''p''<sub>''wh''</sub>
|=  
| =
|wellhead pressure, m/Lt<sup>2</sup>, psia  
| wellhead pressure, m/Lt<sup>2</sup>, psia
|-
|-
|''q''<sub>''g''</sub>  
| ''q''<sub>''g''</sub>
|=  
| =
|gas flow rate, L<sup>3</sup>/t, Mscf/D  
| gas flow rate, L<sup>3</sup>/t, Mscf/D
|-
|-
|''q''<sub>''L''</sub>  
| ''q''<sub>''L''</sub>
|=  
| =
|liquid flow rate, L<sup>3</sup>/t, STB/D  
| liquid flow rate, L<sup>3</sup>/t, STB/D
|-
|-
|''T''<sub>''sc''</sub>  
| ''T''<sub>''sc''</sub>
|=  
| =
|standard temperature, T, °R  
| standard temperature, T, °R
|-
|-
|''T''<sub>''wh''</sub>  
| ''T''<sub>''wh''</sub>
|=  
| =
|wellhead temperature, T, °R  
| wellhead temperature, T, °R
|-
|-
|''y''  
| ''y''
|=  
| =
|ratio of downstream pressure to upstream pressure, ''p''<sub>1</sub>/''p''<sub>2</sub>, dimensionless  
| ratio of downstream pressure to upstream pressure, ''p''<sub>1</sub>/''p''<sub>2</sub>, dimensionless
|-
|-
|Z
| z
|=  
| =
|elevation, L, ft
| gas compressibility factor, dimensionless
|-
|-
|''γ''<sub>''g''</sub>  
| ''γ''<sub>''g''</sub>
|=  
| =
|gas specific gravity, dimensionless  
| gas specific gravity, dimensionless
|}
|}


== References ==


==References==
<references />
<references>
 
<ref name="r1">Beggs, H.D. 1991. ''Production Optimization Using Nodal Analysis'', 123-127. Tulsa, Oklahoma: OGCI Publications. </ref>
== Noteworthy papers in OnePetro ==
<ref name="r2">Gilbert, W.E. 1954. Flowing and Gas-Lift Well Performanc. ''Drill. & Prod. Prac.'', 126-157. Dallas, Texas: API. </ref>
<ref name="r3">Ros, N.C.J. 1960. An Analysis of Critical Simultaneous Gas/Liquid Flow Through a Restriction and Its Application to Flowmetering. ''Applied Scientific Research'' '''9''' (Series A): 374.</ref>
</references>


==Noteworthy papers in OnePetro==
Use this section to list papers in OnePetro that a reader who wants to learn more should definitely read
Use this section to list papers in OnePetro that a reader who wants to learn more should definitely read


==External links==
== External links ==
Use this section to provide links to relevant material on websites other than PetroWiki and OnePetro
 
Xiong, Hongjie. "Optimizing Cluster or Fracture Spacing: An Overview." The Way Ahead. Society of Petroleum Engineers. 25 May 2017. https://www.spe.org/en/twa/twa-article-detail/?art=3007
 
== See also ==
 
[[Nodal_analysis|Nodal analysis]]


==See also==
[[Wellbore_flow_performance|Wellbore flow performance]]
[[Nodal analysis ]]


[[Wellbore flow performance]]
[[Production_system|Production system]]


[[Production system]]
[[PEH:Inflow_and_Outflow_Performance]]


[[PEH:Inflow and Outflow Performance]]
== Category ==
[[Category:3.2 Well operations, optimization, and stimulation]] [[Category:YR]]

Latest revision as of 13:25, 20 June 2017

A wellhead choke controls the surface pressure and production rate from a well. Chokes usually are selected so that fluctuations in the line pressure downstream of the choke have no effect on the production rate. This requires that flow through the choke be at critical flow conditions. Under critical flow conditions, the flow rate is a function of the upstream or tubing pressure only. For this condition to occur, the downstream pressure must be approximately 0.55 or less of the tubing pressure.

Single-phase gas flow

For single-phase gas flow, Beggs[1] presents Eq. 1, which relates the gas production rate through a choke to the wellhead pressure.

RTENOTITLE....................(1)

The pressure ratio, y, is the ratio of the downstream pressure to the wellhead pressure. Under critical flow conditions, the pressure ratio is replaced by the critical pressure ratio, yc. The critical pressure ratio is the pressure ratio at which flow becomes critical. This ratio depends on the ratio of the specific heats of the produced gas, as Eq. 2 shows.

RTENOTITLE....................(2)

Two-phase critical flow

Empirical equations have been developed to estimate the relationship between production rate and wellhead pressure for two-phase critical flow. These correlations can be presented in a form similar to Eq. 3.

RTENOTITLE....................(3)

Gilbert[2] was the first to present such a relationship based on field data collected from the Ten Section field of California. Ros[3] and Beggs[1] have also presented relationships that are often used. Table 1 summarizes the parameters for each equation.


Example

This example illustrates the use of the multiphase choke equation (Eq. 3) to estimate the flowing wellhead pressure for a given set of well conditions. However, this equation can be used to estimate flow rate or choke diameter. The example well is producing 400 STB/D of oil with a gas-liquid ratio of 800 Scf/STB. Estimate the flowing wellhead pressure for a choke size of 12/64 in. with Gilbert’s choke equation.

Solution

Use Eq. 3 and the proper variable from Table 1 to calculate

RTENOTITLE

For these conditions, the estimated flowing wellhead pressure is 1,405 psia. If the Ros choke equation is used, an estimated flowing wellhead pressure of 1,371 psia is calculated. Each of the relationships provides slightly different estimates of the calculated value.

Nomenclature

A1–3 = coefficient in Eq. 3
Cd = discharge coefficient, dimensionless
d = pipe diameter, L, in.
k = specific heat capacity ratio, Cp/Cv in Eqs. 1 and 2, dimensionless
psc = standard pressure, m/Lt2, psia
pwh = wellhead pressure, m/Lt2, psia
qg = gas flow rate, L3/t, Mscf/D
qL = liquid flow rate, L3/t, STB/D
Tsc = standard temperature, T, °R
Twh = wellhead temperature, T, °R
y = ratio of downstream pressure to upstream pressure, p1/p2, dimensionless
z = gas compressibility factor, dimensionless
γg = gas specific gravity, dimensionless

References

  1. 1.0 1.1 Beggs, H.D. 1991. Production Optimization Using Nodal Analysis, 123-127. Tulsa, Oklahoma: OGCI Publications.
  2. Gilbert, W.E. 1954. Flowing and Gas-Lift Well Performanc. Drill. & Prod. Prac., 126-157. Dallas, Texas: API.
  3. Ros, N.C.J. 1960. An Analysis of Critical Simultaneous Gas/Liquid Flow Through a Restriction and Its Application to Flowmetering. Applied Scientific Research 9 (Series A): 374.

Noteworthy papers in OnePetro

Use this section to list papers in OnePetro that a reader who wants to learn more should definitely read

External links

Xiong, Hongjie. "Optimizing Cluster or Fracture Spacing: An Overview." The Way Ahead. Society of Petroleum Engineers. 25 May 2017. https://www.spe.org/en/twa/twa-article-detail/?art=3007

See also

Nodal analysis

Wellbore flow performance

Production system

PEH:Inflow_and_Outflow_Performance

Category