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Continuous Flow Gas Lift DesignContinuous Flow Gas Lift DesignBy Jack R. BlannBy Jack R. Blann

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Petroleum Engineering HandbookPetroleum Engineering Handbook

Gas Lift appears as Chapter 12 in:Gas Lift appears as Chapter 12 in:

Volume IVVolume IVProduction Operations EngineeringProduction Operations Engineering

Edited by Joe Dunn CleggEdited by Joe Dunn Clegg

Chapter 12 was CoChapter 12 was Co--authored by:authored by:Herald W. Winkler, andHerald W. Winkler, andJack R. BlannJack R. Blann

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Two Types of Continuous FlowTwo Types of Continuous FlowGas Lift DesignGas Lift Design

Design for Normal Wells.Design for Normal Wells.

Winkler Design for High gas Injection rates.Winkler Design for High gas Injection rates.

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Iranian Gas Lift WellIranian Gas Lift WellIn In AghaAgha JhariJhari FieldField

Produced: Produced: Natural Flow = 37,000 B/DNatural Flow = 37,000 B/DGas Lift = 43,000 B/DGas Lift = 43,000 B/D

Had 26 mandrels and valves Had 26 mandrels and valves to +3000 ft.to +3000 ft.

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Libyan Gas Lift WellLibyan Gas Lift Well

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Production Manifold in Libya Production Manifold in Libya

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Libyan Gas Lift TestsLibyan Gas Lift Tests

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API Design TechniqueAPI Design Technique

•• Continuous Flow Installation Design Based on Continuous Flow Installation Design Based on Constant Decrease in Operating InjectionConstant Decrease in Operating Injection--Gas Gas Pressure for Each Succeeding Lower Gas Lift Pressure for Each Succeeding Lower Gas Lift ValveValveAll Gas Lift Valves have same port size.All Gas Lift Valves have same port size.There is a constant decrease in the operating There is a constant decrease in the operating injection pressure for each succeeding lower injection pressure for each succeeding lower valve.valve.Port size that allows the injectionPort size that allows the injection--gas gas throughput for unloading and operating the well.throughput for unloading and operating the well.

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This installation design method is This installation design method is recommended for gas lift valves with small recommended for gas lift valves with small productionproduction--pressure factors.pressure factors.When the ratio of the port area to the When the ratio of the port area to the bellows area is low, the decrease in the bellows area is low, the decrease in the injection gas pressure between gas lift injection gas pressure between gas lift valves, based on additional tubing effect valves, based on additional tubing effect pressure for the top valve, is not pressure for the top valve, is not excessive. excessive.

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InjectionInjection--Pressure Operated Gas Lift Pressure Operated Gas Lift ValveValve

Production Pressure Production Pressure factor = factor =

Ratio of Area of Port to Ratio of Area of Port to Area of BellowsArea of Bellows

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Gas Lift Valve SpecificationsGas Lift Valve Specifications

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The effect of bellowsThe effect of bellows--assembly load rate on the assembly load rate on the performance of the valves is not considered in performance of the valves is not considered in the installation design calculations.the installation design calculations.Safety factors included in these calculations Safety factors included in these calculations should allow sufficient increase in the operating should allow sufficient increase in the operating injection gas pressure, which is necessary to injection gas pressure, which is necessary to provide valve stem travel for adequate provide valve stem travel for adequate injectioninjection--gas passage through each successively gas passage through each successively lower unloading valve without interference from lower unloading valve without interference from upper valves.upper valves.

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API Design TechniqueAPI Design TechniqueSelection of a constant injectionSelection of a constant injection-- gas gas pressure decrease, or drop, in the surface pressure decrease, or drop, in the surface operating injection pressure for each operating injection pressure for each succeeding lower gas lift valve should not succeeding lower gas lift valve should not be arbitrary, as proposed in some design be arbitrary, as proposed in some design methods. methods. The pressure decrease should be based on The pressure decrease should be based on the gas lift valve specification to minimize the gas lift valve specification to minimize the possibility of upper valves remaining the possibility of upper valves remaining open while lifting from a lower valve. open while lifting from a lower valve.

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The additional tubingThe additional tubing--effect pressure for effect pressure for the top gas lift valve is a logical choice for the top gas lift valve is a logical choice for this decrease in the operating injectionthis decrease in the operating injection--gas pressure between valves.gas pressure between valves.

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Closing or reopening of an injectionClosing or reopening of an injection--pressurepressure--operated gas lift valve is partially operated gas lift valve is partially controlled by the production pressure controlled by the production pressure effect, which is equal to the production effect, which is equal to the production pressure factor for the valve multiplied by pressure factor for the valve multiplied by the difference in flowing production the difference in flowing production pressure at the top valve depth.pressure at the top valve depth.

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The flowing pressure at an unloadingThe flowing pressure at an unloading--valve depth changes from the transfer valve depth changes from the transfer pressure, (pressure, (PPptfDptfD))minmin, To a higher flowing–production pressure after the next lower valve becomes the operating pressure

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The additional tubingThe additional tubing--effect pressure is effect pressure is the difference between (the difference between (PPptfDptfD))minmin, and the maximum flowing-production pressure at the unlading valve depth, (PPptfDptfD))maxmax, after the point of gas injection has transferred to the next lower valve.

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As the unloading gas lift valve depths As the unloading gas lift valve depths increase , the distance between valves increase , the distance between valves and the difference between (and the difference between (PPptfDptfD))minmin, and (PPptfDptfD))maxmax decrease.decrease.Although the additional tubingAlthough the additional tubing--effect effect pressure decreases for lower valves, the pressure decreases for lower valves, the injectioninjection--gas requirement for unloading gas requirement for unloading increases with depth.increases with depth.

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An increased stem travel, or stroke, is An increased stem travel, or stroke, is usually needed for the lower valves to usually needed for the lower valves to generate the larger equivalent port area generate the larger equivalent port area necessary for the higher injectionnecessary for the higher injection––gas gas requirements with the lower pressure requirements with the lower pressure differentials that occur across these differentials that occur across these deeper valves.deeper valves.

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A constant decrease in the operating A constant decrease in the operating injectioninjection--gas pressure equal to the gas pressure equal to the additional tubing effect pressure for the additional tubing effect pressure for the top valve allows a a greater increase in top valve allows a a greater increase in the injection gas above initial opening the injection gas above initial opening pressure for lower gas lift valves.pressure for lower gas lift valves.

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API Gas Lift DesignAPI Gas Lift Design

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Gradient CurveGradient Curve

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When the injectionWhen the injection--gas pressure significantly gas pressure significantly exceeds the flowingexceeds the flowing-- production pressure, an production pressure, an arbitrary increase in injectionarbitrary increase in injection--gasgas--pressure, pressure, ∆∆PPioio can be added to the initial productioncan be added to the initial production--pressure effect for the top valve for pressure effect for the top valve for calculating the spacing and the initial opening calculating the spacing and the initial opening pressures of the unloading gas lift valvespressures of the unloading gas lift valves

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The total decrease in the injectionThe total decrease in the injection--gas pressure gas pressure is distributed equally between each successively is distributed equally between each successively lower gas lift valve rather than having a sizeable lower gas lift valve rather than having a sizeable pressure drop across the operating gas lift valve pressure drop across the operating gas lift valve or orificeor orifice--check valvecheck valveThis reduces the possibility of multipoint This reduces the possibility of multipoint injection through the upper unloading valves by injection through the upper unloading valves by ensuring that the valves remain closed after the ensuring that the valves remain closed after the point of gas injection has transferred to the next point of gas injection has transferred to the next lower valve,lower valve,

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API Design TechniqueAPI Design TechniqueDetermination of Valve DepthsDetermination of Valve Depths

Because the final injection gas pressure is Because the final injection gas pressure is not known until the installation is not known until the installation is designed, a pressure difference of 100 to designed, a pressure difference of 100 to 200 psi between the unloading 200 psi between the unloading PPioDioD and and PPpfDpfD traverses is assumed for locating the traverses is assumed for locating the deepest valve depth.deepest valve depth.

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The assumption of The assumption of PPioDioD--PPpfDpfD = = 100 to100 to 200 200 psi should ensure calculation of the psi should ensure calculation of the operating valve depth.operating valve depth.The static The static bottomholebottomhole pressure, pressure, PPwsDwsD and and temperature, temperature, TTwsdwsd are usually referenced are usually referenced to the same depth, which is the lower end to the same depth, which is the lower end of the production conduit, of the production conduit, DDdd..

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Calculate the maximum unloading GLR Calculate the maximum unloading GLR based on the maximum injection gas rate based on the maximum injection gas rate available for unloading and the maximum available for unloading and the maximum daily design total fluid rate.daily design total fluid rate.

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Well InformationWell InformationTubing size = 2 7/8 Tubing size = 2 7/8 ––in. ODin. ODTubing Length, Tubing Length, УУ = 6000 ft.= 6000 ft.Max. Valve Depth, Max. Valve Depth, DDv(maxv(max) ) = 5970 ft.= 5970 ft.Static Static bottomholebottomhole pressure at pressure at DDdd , , PPwsdwsd = 1800 psig at = 1800 psig at 6000ft.6000ft.Daily production rate = 800 STB/DDaily production rate = 800 STB/DWater Cut = 50%Water Cut = 50%Formation GOR = 500 Formation GOR = 500 scfscf/STB/STBOil Gravity = 35Oil Gravity = 35o o APIAPIGas Gravity Gas Gravity УУgg = 0.65= 0.65ProducedProduced--water specific gravity, water specific gravity, УУww= 1.08= 1.08BottomholeBottomhole temperature, temperature, TTwsdwsd=170=170ooF at 6000ft.F at 6000ft.Design unloading wellhead temperature, Design unloading wellhead temperature, TTwhfwhf = 100= 100ooF.F.LoadLoad--fluid pressure gradient, fluid pressure gradient, gglsls = 0.46 psi/ft.= 0.46 psi/ft.UU--Tubing wellhead pressure,Tubing wellhead pressure, PPwhuwhu = 100 psig.= 100 psig.Flowing wellhead pressure,Flowing wellhead pressure, PPwhfwhf = 100 psig.= 100 psig.

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Well InformationWell InformationStatic fluid level = 0 ft.Static fluid level = 0 ft.Surface kickoff injectionSurface kickoff injection--gas pressure, gas pressure, PPkoko = 1000 psig.= 1000 psig.Surface operating injectionSurface operating injection--gas pressure, gas pressure, PPioio = 1000 = 1000 psig.psig.Maximum unloading injectionMaximum unloading injection--gas rate, gas rate, qqgiugiu = 800 = 800 MscfMscf/D./D.Operating daily injectionOperating daily injection--gas rate, gas rate, qqgigi = 500 = 500 MscfMscf/D./D.Wellhead injectionWellhead injection--gas temperature, gas temperature, TTgiogio = 100= 100ooFFAssigned valveAssigned valve--spacing pressure differential at valve spacing pressure differential at valve depth, depth, ∆∆PPsDsD = = 50 psi.50 psi.Test rack valve temperature, Test rack valve temperature, TTvovo = 60= 60ooF.F.Assigned minimum decrease in surface operating Assigned minimum decrease in surface operating injectioninjection--gas pressure between valves, gas pressure between valves, ∆∆PPioio = 20 psi.= 20 psi.Minimum distance between valves, Minimum distance between valves, DDbv(minbv(min) ) = 150 ft.= 150 ft.Gas lift valves : 1.5 inch O.D. nitrogen charged with Gas lift valves : 1.5 inch O.D. nitrogen charged with AAbb = = 0.77 in0.77 in22, and sharp edged seat., and sharp edged seat.

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Step 1:Step 1:Calculate Maximum Unloading GLRCalculate Maximum Unloading GLR

RRgiugiu ==qqgiugiu / / qqltlt

Where Where qqgiugiu= maximum unloading injection rate, = maximum unloading injection rate,

MscfMscf/D,/D,qqltlt = total liquid daily production rate, = total liquid daily production rate,

B/D, and B/D, and RRgiugiu = maximum unloading GLR, = maximum unloading GLR, scfscf/STB/STB

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API Design TechniqueAPI Design TechniqueCalculate Maximum Unloading GLRCalculate Maximum Unloading GLR

RRgiugiu ==qqgiugiu / / qqltlt

= 800,000 = 800,000 scfscf/D / 800 STB/D /D / 800 STB/D RRgiugiu = 1000 = 1000 scfscf/STB /STB

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Step 2: Determine flowing Production Step 2: Determine flowing Production pressure, pressure, PPpfdpfd at at DDdd

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Step 3:Calculate the Step 3:Calculate the unloadingunloading--flowingflowing--pressurepressure--atat--depth depth gradient, gradient, ggpfapfa above above point of gas injection, point of gas injection, ggpfpf ..

ggpfapfa = 900= 900--100 / 6000 100 / 6000 ggpfapfa = 0.1333 psi/ ft.= 0.1333 psi/ ft.

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Step 4Step 4Calculate the operating injection gas pressure at the lower end Calculate the operating injection gas pressure at the lower end of the of the

production conduit.production conduit.where: where:

PPioio = injection= injection--gas pressure at surface, gas pressure at surface, psiapsiaPPioDioD == injectioninjection--gas pressure at depth, gas pressure at depth, psiapsiaee = = NapierianNapierian logarithm base = 2.718logarithm base = 2.718……..γγgg = gas specific gravity (air = 1.0), dimensionless.= gas specific gravity (air = 1.0), dimensionless.DD = true vertical depth of gas column, ft.= true vertical depth of gas column, ft.

bar Tbar T = average gas column temperature, = average gas column temperature, °°RRbar z = compressibility factor based on gas column averagbar z = compressibility factor based on gas column average e

pressure P and temperature, T, dimensionless. pressure P and temperature, T, dimensionless.


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Step 4Step 4PPioDioD = 1154 psig at 6000 ft.= 1154 psig at 6000 ft.gggiogio = (1154 = (1154 –– 1000) / 6000 = .0257psi/ft1000) / 6000 = .0257psi/ft

Since Since PPiodiod -- PPpfdpfd = 1154 = 1154 –– 900 = 254 psi900 = 254 psiExceeds 200 psi, the maximum valve depth Exceeds 200 psi, the maximum valve depth

of 5970 ft can be attained.of 5970 ft can be attained.

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Step 5:Step 5:Calculate the unloading gas lift valve Calculate the unloading gas lift valve temperature at depth gradient,temperature at depth gradient, ggTvuTvu ..

BottomholeBottomhole temperature,temperature,TTwsdwsd =170=170ooF at 6000ft.F at 6000ft.

Design unloading wellhead temperature, Design unloading wellhead temperature, TTwhfwhf = 100= 100ooF at surface.F at surface.

ggTvuTvu = (170 = (170 –– 100) / 6000 = 0.0117100) / 6000 = 0.0117ooF/ft.F/ft.

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Step 6Step 6DDv1 v1 = depth of top valve, ft= depth of top valve, ftPPkoko = surface kick= surface kick--off or average field injectionoff or average field injection--gas pressure gas pressure

(optional), psig(optional), psigPPwhuwhu = surface wellhead U= surface wellhead U--tubing (unloading) pressure, psigtubing (unloading) pressure, psig∆∆PsDPsD = assigned spacing pressure differential at valve depth, psi= assigned spacing pressure differential at valve depth, psi

wherewheregglsls = static= static--load (kill) fluid pressure gradient, psi/ftload (kill) fluid pressure gradient, psi/ftgggiogio = injection= injection--gas pressure at depth gradientgas pressure at depth gradient, , psi/ftpsi/ft

Step 6:Step 6:DDv1 v1 = = (1000 (1000 -- 100 100 –– 50) / (0.46 50) / (0.46 --.0257).0257)DDv1 v1 = = 1957 ft.1957 ft.

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Step 7Step 7Calculate the minimum flowingCalculate the minimum flowing--production production pressure, pressure, (P(PpfD1pfD1)min)min, the injection, the injection--gas gas pressure, pressure, PPioD1ioD1, and the unloading gas, and the unloading gas--lift lift valve temperature, valve temperature, TTvuD1vuD1, at the top valve , at the top valve depth by multiplying the appropriate depth by multiplying the appropriate gradient by the valve depth, gradient by the valve depth, DDv1v1, and , and adding to the appropriate surface values adding to the appropriate surface values (where n = 1 for top valve): (where n = 1 for top valve):

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Step 7.Step 7.Calculate the minimum flowingCalculate the minimum flowing--production production pressure, (pressure, (PPpfDpfD1)min, injection1)min, injection--gas pressure,gas pressure,PioD1PioD1, and the unloading flowing temperature, , and the unloading flowing temperature, TTvuDvuD11 at at DDv1v1 of 1,957 ft as described on previous of 1,957 ft as described on previous slide:slide:((PPpfD1pfD1)min = 100 + 0.1333 (1,957) = 361 psig)min = 100 + 0.1333 (1,957) = 361 psigPPioD1ioD1 == 1,000 + 0.0257 (1,957) = 1,050 psig1,000 + 0.0257 (1,957) = 1,050 psigTTvuD1vuD1 = 100 + 0.0117 (1,957) = 123 = 100 + 0.0117 (1,957) = 123 °°FF

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API Design TechniqueAPI Design TechniqueStep 8Step 8

•• Calculate the depth of the second gasCalculate the depth of the second gas--lift lift valve, valve, DDv2v2, where n = 2 on the basis of the , where n = 2 on the basis of the assigned minimum decrease in surface injectionassigned minimum decrease in surface injection--gas pressure,gas pressure, ∆∆ppioio,, for spacing the gasfor spacing the gas--lift valves lift valves and the and the PPioDioD--traverse. traverse.

•• A valve spacing differential of around 20 to 30 A valve spacing differential of around 20 to 30 psi will usually be sufficient for most 1.5psi will usually be sufficient for most 1.5--in. OD in. OD gasgas--lift valves. However, 1lift valves. However, 1--in. OD valves with in. OD valves with large ports may require a higher, large ports may require a higher, ∆∆ppioio. This can . This can be checked by calculating the additional be checked by calculating the additional productionproduction--pressure effect, pressure effect, ∆∆PPpe1pe1, after the valve , after the valve depths are calculated for the assigned depths are calculated for the assigned ∆∆ppioio. .

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((PPpfD(npfD(n--1)1)))minmin++gglsls((DDbvbv)=[)=[PPioD(nioD(n--1)1)--(n(n--1)1)∆∆PPioio]]-- ∆∆PPsDsD ++gggiogio((DDbvbv))

Solve For Solve For DDbvbv::

DDbvbv = = PPioD(nioD(n--1)1) –– [(n[(n--1)1)∆∆PPioio]]-- ((PPpfD(npfD(n--1)1)))minmin -- ∆∆PPsDsD / (/ (gglsls ––gggiogio

andandDDv(nv(n) ) = = DDv(nv(n--1) 1) + + DDbvbv

The decrease in surface injectionThe decrease in surface injection--gas pressure for gas pressure for calculating Dcalculating Dv2v2 is is ∆∆PPioio, and for D, and for Dv3v3 is 2 (is 2 (∆∆PPioio), and for D), and for Dv4v4is 3 (is 3 (∆∆PiPioo), and this procedure continues for each ), and this procedure continues for each succeeding lower valve.succeeding lower valve.

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Solve For Solve For DDbvbv::DDbvbv = = PPioD(nioD(n--1)1) –– [(n[(n--1)1)∆∆PPioio]]-- ((PPpfD(npfD(n--1)1)))minmin -- ∆∆PPsDsD / (/ (gglsls ––gggiogio

DDbvbv = 1050 = 1050 -- 0 0 -- 361 361 –– 50 / (0.46 50 / (0.46 –– 0.0257) = 1472 ft.0.0257) = 1472 ft.

andand

DDv(2) v(2) = = DDv(nv(n--1) 1) + + DDbvbv

DDv(2)v(2) = 1957 + 1472 = 3429 ft.= 1957 + 1472 = 3429 ft.

Repeat steps 7 and 8 for each valve location until reaching Repeat steps 7 and 8 for each valve location until reaching maximum depthmaximum depth

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The calculated valve spacing for the sixth The calculated valve spacing for the sixth valve, valve, DDv6v6 , would exceed the maximum , would exceed the maximum valve depth,valve depth, DDv(maxv(max) ) , of 5,970 ft. Because , of 5,970 ft. Because an orificean orifice--check valve will be placed in the check valve will be placed in the bottom bottom wirelinewireline--retrievable valve mandrel, retrievable valve mandrel, no testno test--rack valve setting information is rack valve setting information is required. This completes the valve spacing required. This completes the valve spacing calculations. calculations.

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API Design TechniqueAPI Design TechniqueGraphical RepresentationGraphical Representation

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API Design TechniqueAPI Design TechniqueDetermination of GasDetermination of Gas--Lift Valve Port Size and Lift Valve Port Size and Calculation of TestCalculation of Test--Rack Opening PressuresRack Opening Pressures..

The gasThe gas--lift valves port ID and testlift valves port ID and test--rack opening rack opening pressure calculations follow:pressure calculations follow:

Step 1. Determine the port size required for the gasStep 1. Determine the port size required for the gas--lift lift unloading valves and the operating orificeunloading valves and the operating orifice--check valve check valve orifice ID. The upstream injectionorifice ID. The upstream injection--gas pressure, gas pressure, PP11, is , is based on based on PPoD5oD5 of the last unloading valve corrected to of the last unloading valve corrected to the orificethe orifice--check valve depth of 5970 ft:check valve depth of 5970 ft:

PP11 = 1,068 + 0.0257 (5,970 = 1,068 + 0.0257 (5,970 –– 5,762) = 1,073 psig at 5,762) = 1,073 psig at 5,970 ft5,970 ft

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Determination of GasDetermination of Gas--Lift Valve Port Size Lift Valve Port Size and Calculation of Testand Calculation of Test--Rack Opening Rack Opening PressuresPressures..

Step 1 (Continued)Step 1 (Continued)The downstream flowingThe downstream flowing--production pressure, production pressure, PP22, is equal to the minimum flowing, is equal to the minimum flowing--production production pressure at 5,970 ft.pressure at 5,970 ft.PP22 = 100 + 0.1333 (5,970) = 896 psig at 5,970 = 100 + 0.1333 (5,970) = 896 psig at 5,970 ftft∆∆PPovov = 1,073 = 1,073 –– 896 = 177 psi across the orifice896 = 177 psi across the orifice--check valvecheck valve

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Step 1 (Continued)Step 1 (Continued)From the From the ThornhillThornhill / Craver correlation, the required / Craver correlation, the required equivalent orifice size is near 14/64equivalent orifice size is near 14/64--in.; therefore, the in.; therefore, the next largest gasnext largest gas--lift valve port ID is 1/4lift valve port ID is 1/4--in. This size is in. This size is sufficient for all of the upper unloading valves because sufficient for all of the upper unloading valves because they have a higher injectionthey have a higher injection--gas operating pressure and gas operating pressure and a greater differential pressure between a greater differential pressure between PiPioDoD andand((PPpfDpfD)min)min. .

An equivalent orifice size of 12/64An equivalent orifice size of 12/64--in. to 13/64in. to 13/64--in. is in. is required to pass the operating injectionrequired to pass the operating injection--gas rate of 500 gas rate of 500 MscfMscf/D./D.

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API Design TechniqueAPI Design TechniqueDetermination of GasDetermination of Gas--Lift Valve Port Size and Lift Valve Port Size and Calculation of TestCalculation of Test--Rack Opening PressuresRack Opening Pressures..Step2Step2Record the valve specifications for a l.5Record the valve specifications for a l.5--in. OD in. OD gasgas--lift valve having a 1/4lift valve having a 1/4--in. ID port with a in. ID port with a sharpsharp--edged seat where edged seat where AAbb = 0.77 sq. in. = 0.77 sq. in.

from table: from table: ((AAp/p/AAbb) = 0.064,) = 0.064,

(1 (1 –– AApp //AAbb) ) = 0.936,= 0.936,and and FFpp = 0.068.= 0.068.

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Step 3Step 3Calculate Calculate PPoDoD1 1

PPoD1oD1 = = PPioD1ioD1

wherewherePPioD1ioD1 = injection= injection--gas pressure at valve depth, psiggas pressure at valve depth, psigPPoD1oD1 = injection= injection--gas initial gasgas initial gas--lift valve opening lift valve opening

pressure at valve depth, psigpressure at valve depth, psigPPoDoD11 = 1,050 psig at 1,957 ft= 1,050 psig at 1,957 ft

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Step4 Step4 Calculate the testCalculate the test--rack set opening pressure of rack set opening pressure of the first valve (n = 1), the first valve (n = 1), PPvo1vo1, using , using EqsEqs. 12.44 . 12.44 and 12.45 or 12.46:and 12.45 or 12.46:

PPbvD(nbvD(n) ) = = PPoD(noD(n) ) (1(1--AApp/A/Abb)+ )+ PPpfD(n)minpfD(n)min +(+(AApp//AAbb) ) PPvo(nvo(n) ) == CCT(nT(n) ) ((PPbvD(nbvD(n))) / (1) / (1-- AApp//AAbb))

PPvo(nvo(n) ) = 1050 (0.936)+361 (0.064) = 1006 psig. = 1050 (0.936)+361 (0.064) = 1006 psig.

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Step 5Step 5PPvo(nvo(n) ) == CCT(nT(n) ) ((PPbvD(nbvD(n))) / (1) / (1-- AApp//AAbb))

for for CCT1T1 = 0.876 (Calculated using = 0.876 (Calculated using TTvuD1vuD1 = = 123123ooF):F):PPvo1vo1 = 0.876 (1006)/0.936 = 942 psig at 60 = 0.876 (1006)/0.936 = 942 psig at 60 ooFF

Step 6Step 6Calculate the injectionCalculate the injection--gas initial opening pressure gas initial opening pressure of the second gasof the second gas--lift valve at depth (n = 2), lift valve at depth (n = 2),

PPoD(noD(n) ) = = PPioD(nioD(n) ) –– (n(n--1) 1) ∆∆PPioioPPoD(2) oD(2) = 1088 = 1088 –– 20 = 1068 psig at 3429 ft.20 = 1068 psig at 3429 ft.

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Calculate the maximum flowingCalculate the maximum flowing--production production pressure opposite top unloading valve pressure opposite top unloading valve immediately after the point of gas injection has immediately after the point of gas injection has transferred to the second (lower) valve, transferred to the second (lower) valve, ((PPpfD1pfD1))maxmax. (. (PPpfD1pfD1 ))maxmax is shown graphically in is shown graphically in Figure and can be calculated using the following Figure and can be calculated using the following equation:equation:((PPpfD1pfD1))max max = = PPwfwf + + DDv1 v1 [([(PPoD2 oD2 –– PPwhfwhf )/)/DDv2v2]]((PPpfD1pfD1))max max = 100 + 1957 ((1068 = 100 + 1957 ((1068 --100)/3429) 100)/3429) ((PPpfD1pfD1))max max = 652 psig at 1957 ft.= 652 psig at 1957 ft.

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Step 8Step 8Determine if the assumed decrease in surface injectionDetermine if the assumed decrease in surface injection--gas pressure, gas pressure, ∆∆PPioio, is sufficient for the required gas, is sufficient for the required gas--lift lift valve port size by calculating the additional productionvalve port size by calculating the additional production--pressure effect, pressure effect, ∆∆PPpe1pe1, at the top valve:, at the top valve:∆∆PPpe1 pe1 = = FFpp [[((PPD1D1)maxD1D1)max -- PPD1D1)minD1D1)min ]]∆∆PPpe1pe1 = 0.068 (652 = 361 = 20 psi. = 0.068 (652 = 361 = 20 psi.

If If ∆∆PPpe1 pe1 is less than or equal to the assumed is less than or equal to the assumed ∆∆PPioioproceed with the design. If proceed with the design. If ∆∆PPpe1pe1 is greater than theis greater than theassumed assumed ∆∆PPioio, then set , then set ∆∆PPioio = = ∆∆PPpe1pe1 and redo the spacing and redo the spacing design. This is a conservative approach and many design. This is a conservative approach and many operators use actual operating experience to determine operators use actual operating experience to determine which which ∆∆PPioio to use.to use.

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Repeat Steps 6, 4 and 5 for remaining Repeat Steps 6, 4 and 5 for remaining gasgas--lift valves: lift valves: An orificeAn orifice--check valve is recommended for check valve is recommended for the sixth valve at 5,962 ft. The orifice ID the sixth valve at 5,962 ft. The orifice ID should be 1/4should be 1/4--in. to pass sufficient gas to in. to pass sufficient gas to gas lift the well. A tabulation form for gas lift the well. A tabulation form for these calculations is given in table.these calculations is given in table.

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High Rate ContinuousHigh Rate Continuous--Flow Installation Flow Installation Design ( Winkler)Design ( Winkler)

The application of the injectionThe application of the injection--gas rate throughput gas rate throughput performance for injectionperformance for injection--pressurepressure--operated gasoperated gas--lift valves is lift valves is illustrated in the high daily liquid rate continuousillustrated in the high daily liquid rate continuous--flow flow installation design. The importance of valve performance data installation design. The importance of valve performance data for high daily injectionfor high daily injection--gas rates is shown, and its gas rates is shown, and its unimportance for low injectionunimportance for low injection--gas rate installation designs is gas rate installation designs is illustrated. Valve performance data is of no value in selection illustrated. Valve performance data is of no value in selection of of the top two unloading gasthe top two unloading gas--lift valves in this installation. For lift valves in this installation. For these two upper valves, an assumed reasonable decrease in these two upper valves, an assumed reasonable decrease in the surface injectionthe surface injection--gas pressure of 20 psi for each valve gas pressure of 20 psi for each valve ensures unloading the well and these upper valves remaining ensures unloading the well and these upper valves remaining closed while lifting from a lower valve. When the required dailyclosed while lifting from a lower valve. When the required dailyinjectioninjection--gas rate increases for lifting from the third and fourth gas rate increases for lifting from the third and fourth gasgas--lift valves, valve performance information becomes very lift valves, valve performance information becomes very important. A pressure vs. depth plot for this continuousimportant. A pressure vs. depth plot for this continuous--flow flow installation is shown ininstallation is shown in the Figurethe Figure

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High Rate ContinuousHigh Rate Continuous--Flow Installation Flow Installation Design ( Winkler)Design ( Winkler)

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High Rate ContinuousHigh Rate Continuous--Flow Installation Flow Installation Design (Winkler)Design (Winkler)

Although the flowingAlthough the flowing--production transfer pressure traverse production transfer pressure traverse method for locating the depths of the valves may require an method for locating the depths of the valves may require an additional valve, or valves, in some installations, this design additional valve, or valves, in some installations, this design method has several advantages in wells requiring a high daily method has several advantages in wells requiring a high daily injectioninjection--gas rate for unloading. Because the injectiongas rate for unloading. Because the injection--gas gas requirement to uncover the next lower valve is reduced, smaller requirement to uncover the next lower valve is reduced, smaller valve ports can be used and the increase in the injectionvalve ports can be used and the increase in the injection--gas gas pressure to stroke the valve stem is less. The unloading pressure to stroke the valve stem is less. The unloading operations are faster because of the lesser difference in operations are faster because of the lesser difference in injectioninjection--gas requirement between unloading valves. gas requirement between unloading valves.

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High Rate ContinuousHigh Rate Continuous--Flow Flow Installation Design Installation Design ( Winkler)( Winkler)

The surface origin and final The surface origin and final downholedownholetermination pressures for the flowingtermination pressures for the flowing--production production transfer pressure traverse are arbitrary. The transfer pressure traverse are arbitrary. The 20% in this example for locating the surface 20% in this example for locating the surface transfer pressure traverse is widely used. The transfer pressure traverse is widely used. The unloading injectionunloading injection--gas requirements for gas requirements for uncovering each lower valve increases as the uncovering each lower valve increases as the percentage decreases and decreases as the percentage decreases and decreases as the percentages increase. The flowingpercentages increase. The flowing--production production transfer pressure at datum depth should be at transfer pressure at datum depth should be at least 100 to 200 psi less than the available least 100 to 200 psi less than the available design operating injectiondesign operating injection--gas pressure at the gas pressure at the same depth same depth

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Simplified Mathematical GasSimplified Mathematical Gas--Lift Valve Lift Valve Performance ModelPerformance Model

Because performance equations for specific gasBecause performance equations for specific gas--lift lift valves are not available from gasvalves are not available from gas--lift valve lift valve manufacturers, a simplified gasmanufacturers, a simplified gas--lift valve lift valve performance computer model was used to performance computer model was used to illustrate the calculations in this paper. The illustrate the calculations in this paper. The model is based on static force balance equations model is based on static force balance equations and several simplifying assumptions. This and several simplifying assumptions. This computer model describes qualitatively the computer model describes qualitatively the injectioninjection--gas rate throughput of unbalanced, gas rate throughput of unbalanced, singlesingle--element gaselement gas--lift valves using the lift valves using the ThornhillThornhill--Craver equation.Craver equation.

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High Rate Design DataHigh Rate Design DataTubing size = 4Tubing size = 4--1/21/2--in. OD (ID = 3.958in. OD (ID = 3.958--in.) and Length = 6,000 ftin.) and Length = 6,000 ftCasing size = 8Casing size = 8--5/85/8--in. OD, 44 lb/ft (ID = 7.725in. OD, 44 lb/ft (ID = 7.725--in.) in.) Datum depth for Datum depth for bottomholebottomhole pressures and temperature, pressures and temperature, DDdd = 6,000 ft= 6,000 ftBottomholeBottomhole temperature at temperature at DDdd,, TTwsdwsd = 170 = 170 oFoFShutShut--in (static) in (static) bottomholebottomhole pressure at pressure at DDdd,, PPwsdwsd = 2,000 psig= 2,000 psigMaximum depth for bottom valve, Maximum depth for bottom valve, DDv(maxv(max)) = 5,900 ft= 5,900 ftProductivity index (gross liquid), Productivity index (gross liquid), PI PI = 6.3 BPD/psi= 6.3 BPD/psiOil gravity = 35 Oil gravity = 35 ooAPIAPI ((γγoo = 0.850)= 0.850)Gas specific gravity (air = 1.0), Gas specific gravity (air = 1.0), γγgg = 0.65= 0.65Water specific gravity, Water specific gravity, γγww = 1.08= 1.08Water fraction, Water fraction, ffww = 0.50 (50%)= 0.50 (50%)Formation gas/oil ratio, Formation gas/oil ratio, RRgogo = 400 = 400 scfscf/STB/STBFormation gas/liquid ratio, Formation gas/liquid ratio, RRglfglf = 200 = 200 scfscf/STB/STBAssigned minimum daily unloading production rate, Assigned minimum daily unloading production rate, qqlulu = 1,000 BPD= 1,000 BPDDesign total (oil + water) daily production rate, Design total (oil + water) daily production rate, qqltlt = 5,000 BPD= 5,000 BPDWellhead UWellhead U--tubing unloading pressure, tubing unloading pressure, PPwhuwhu = 100 psig= 100 psigSurface flowing wellhead pressure, Surface flowing wellhead pressure, PPwhfwhf = 100 psig= 100 psigStatic load (kill) fluid pressure gradient, Static load (kill) fluid pressure gradient, gglsls = 0.468 psi/ft= 0.468 psi/ft

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High Rate Design Data (Continued)High Rate Design Data (Continued)Surface operating injectionSurface operating injection--gas pressure, gas pressure, PPioio = 1,400 psig (at = 1,400 psig (at wellsitewellsite))Assigned daily injectionAssigned daily injection--gas rate, gas rate, qqgigi = 2,000 = 2,000 MscfMscf/day/dayUnloading wellhead temperature, Unloading wellhead temperature, TTwhuwhu = 120= 120ooF (basis for calculation of F (basis for calculation of PvoPvo))Wellhead injectionWellhead injection--gas temperature, gas temperature, TTgiogio = 120= 120ooFFSurface kickoff injectionSurface kickoff injection--gas pressure, gas pressure, PPkoko = 1,400 psig (at = 1,400 psig (at wellsitewellsite))Minimum assigned surface injectionMinimum assigned surface injection--gas pressure decrease between valves, gas pressure decrease between valves, ∆∆PPioio = 20 psi (represents minimum surface injection= 20 psi (represents minimum surface injection--gas pressure increase gas pressure increase for stroking gasfor stroking gas--lift valve)lift valve)Valve spacing design line percent factor at surface = 20% (Valve spacing design line percent factor at surface = 20% (ffptpt = 0.20)= 0.20)Minimum transferMinimum transfer--production pressure difference (production pressure difference (PPiodiod –– PPptdptd) at ) at DDdd, , ∆∆PPptdptd = = 200 psi200 psiValve spacing pressure differential at valve depth, Valve spacing pressure differential at valve depth, ∆∆PPsDsD = 50 psi= 50 psiMinimum distance between valves Minimum distance between valves DDbv(minbv(min)) = 400 ft= 400 ftGasGas--lift valve testlift valve test--rack setting temperature, rack setting temperature, TTvovo = 60 = 60 oFoFGasGas--lift valves: 1.5lift valves: 1.5--in. OD in. OD wirelinewireline--retrievable, unbalanced, singleretrievable, unbalanced, single--element, element, nitrogennitrogen--charged bellows with charged bellows with AAbb = 0.77 in.2, = 0.77 in.2, BBlrlr = 600 psi/in., and square = 600 psi/in., and square sharpsharp--edged seat.edged seat.

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Valve Performance Valve Performance –– First ValveFirst Valve

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Valve Performance Valve Performance –– First ValveFirst Valve

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Winkler High Rate Gas Lift DesignWinkler High Rate Gas Lift Design

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Continuous Flow Gas Lift DesignContinuous Flow Gas Lift Design

As Presented inAs Presented in2007 SPE PRODUCTION 2007 SPE PRODUCTION

ENGINEERING HANDBOOKENGINEERING HANDBOOK

continuous flow gas lift design - alrdc - home 9 api design technique • continuous flow...

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