Gas Lift Wellflo

8/17/2019 Gas Lift Wellflo

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EX 5 1Example 5

FloSystem User Course

Gaslift Design and Analysis


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EX 5 2Gaslift Design

Overview• A Gaslift design for a well that does not flow naturally• Select Data Preparation and check :

– Reservoir data – Fluid data – Deviation data - Well data – Equipment Data - Well Data


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EX 5 3Reservoir DataEnter Reservoir Data

• Fluid Type is Black Oil• Entry Model is Manual

– PI = 1.3 STB/day/psia – IPR model = Vogel – Reservoir Pressure = 5100 psia – Reservoir Temperature = 230 F

• Fluid Parameters for Black Oil – API = 27.5 – GOR = 320 – Water cut = 20 % – Gas specific gravity = 0.74 –

Water salinity = 200 kppm


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EX 5 4Deviation Data


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EX 5 6Analysis :Operating Point


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EX 5 7No operating point:Natural flow


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EX 5 8Gaslift Data

• Select Data Preparation - Gaslift Data• Use the following design parameters :

– Casing Injection Pressure = 1200 psia –

Gas Specific Gravity = 0.65 – Differential pressure across the Valve = 100 psia – Lift gas injection rate 1.5 MMscf/day – Deepest point of injection = 40 ft above tubing shoe

• These are the minimum data to calculate theOperating Point for the‘Deepest Point of Injection’


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EX 5 9Gaslift Design :Deepest Injection Point


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EX 5 10Gaslift Design Rate2513 STB/day


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EX 5 11Pressure vs DepthInjection Depth: 8120 ft TVD


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EX 5 13Sensitivity of lift gasinjection rate

Note PaybackRatio


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EX 5 14Sensitivity of anincreasing water cut


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EX 5 15Gaslift Design :Final Parameters•

The final parameters for the optimum design willdepend of the actual operating restrictions.• The initial lift gas injection rate, casing injection

pressure and valve differential pressure will be used

for the Gaslift DesignSelect Analysis - Gaslift Design ....• Revise the parameters again and set the top node or

Christmas tree pressure and the specific gravity ofthe fluid in the annulus


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EX 5 18Design Margins....Casing Controlled Valves + ValveNumber

•

Casing Controlled Valves and Valve Number

Additionally• The fluid in the annulus is brine of 0.45 psi/ft• Minimum valve spacing below the operating valve =

450 ft. (100 psi)


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EX 5 19Gaslift Design...Design Margins...

Kick off Pressure

Casing closingpressure margin

Margin at valve 1

Increment per valve


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EX 5 20

Gaslift Design...Gaslift Valves Spacing


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EX 5 21Gaslift Design...Gaslift Valves Spacing

Operating Valve with alldesign margins

Design Operating valve

Minimum valve spacing


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EX 5 22

Gaslift Design...Spacing of Design OperatingValve

The position of the Design Operating valve depends ifthe spacing finds the following constraints:

1. Next position less than “ minimum valve spacing” • Last valve is marked as Operating valve and valve

spacing below equal to “minimum spacing”.• The Design Operating valve is marked at depth with

enough differential pressure (relative to uncorrectedtubing pressure)


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EX 5 23


2. Pcasing- Ptubing< differential pressureMove up until it reaches a depth where thedifferential pressure is met

• The new position is the Design operatingvalve if spacing greater than “minimum valvespacing”

• If the new position is less than “minimum

valve spacing” the Design Operating valve ismarked at the valve above


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EX 5 24


3. Next position is below Max MD of injection

• The Design Operating valve will be positioned at MaxMd provided Pcasing-Ptubing> valve differential

pressure• If Pcasing-Ptubing


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EX 5 25Gaslift Design Results

•

Active valves 6 and dummy valves 12• 5 unloading valves• 1 operating valve :

– Valve Depth = 7621 ft TVD (8068 ft MD) – Casing Pressure = 1300 psia – Tubing Pressure = 1195 psia – Temperature = 212.4 oF

•

12 Dummy valves below the operating valve spacedat 450 ft (TVD)


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EX 5 26Gaslift Design Results

• A new casing injection operating pressure of1131 psia can be selected

• However this new injection pressure will give aliquid rate = 2434 STB/day because

•

If the casing injection pressure is kept at 1200psi, then the liquid rate = 2491 STB/day(compared with design value of 2513 STB/day)


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EX 5 27Sizing.... Facility

1. Port Size calculation using the Thornhill Craverequation.

2. Opening and Closing pressures computation foreach valve

3. Dome and Test Rack Opening pressurescomputation for each valve

4. Valve type selection : – Gas Charged – Spring – Orifice


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EX 5 28

Sizing.... Facility

Gaslift Design... results transferred to Sizing...:Column name• Gaslift rate Qgi • Valve depths MD and TVD• Wellbore temperature Temp• Tubing transfer pressure Pt P tubing • Casing pressure Pvo P open valve


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EX 5 29

Sizing.... Facility

1. Port Size

Valve type and Port SizeValve type and Port Size

Critical Flow FlagCritical Flow Flag

PtPt

PvoPvo


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EX 5 30

Sizing.... Facility

1. Port Size

Thornhill-Craver is solved with:• Pt (downstream pressure)• Pvo (upstream pressure)• Temp• Qgi• Discharge coefficient ( Disch Coeff column) default

value is 0.865

All these values can be edited independent of theprevious gaslift design results

• The column Crit shows whether the valve is oncritical flow


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EX 5 31

Sizing.... Casing controlled

2. Opening and Closingpressures

Two methods to determine Opening and Closingpressures:

A. Use Pvo (from Gaslift Design)B. Specify a surface closing pressure Psc

– (P close surf , column)

• Update ratio R = tubing port area /bellows area• R in the order of 0.1 i.e. most of the bellows “feel” thecasing pressure


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EX 5 32



A. Use Pvo by setting NO in Calc by P closespreadsheet column

B. Use P close surf by setting YES in Calc by P closespreadsheet column

Select calculation method


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EX 5 33



A. Use Pvo:• The Dome pressure is calculated from:

Pd = Pvo(1- R)+Pt(R)• The Valve Closing pressure Pvc is equal to Pd.

– Pd & Pc valve column in spreadsheet• The surface Closing pressure Psc follows by

correcting Pvc for the gas gradient –

P close surf column in spreadsheet• The surface Opening pressure Pso follows by

correcting Pvo for the gas gradient


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EX 5 34

PvcPsc



Pt

R

PvoPvo PsoPso


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EX 5 35


2. Opening and ClosingpressuresB. Use P close surf (Psc)• Enter the Psc in the spreadsheet (e.g. 1300 for the

first valve)• The Pvc is computed by using the gas gradient

and Psc. By definition this is the in-situ domepressure Pd – Pd & Pc valve column in spreadsheet

• The valve Opening pressure Pvo is calculated from

Pd, R and Pt:Pvo= (Pd-Pt*R) /(1-R)

– P open valve column – P open surf (Pso) follows by correcting Pvo for the gas

gradient


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EX 5 36

B. Use P close surf ( Psc)



YesPsc


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EX 5 37


3. Pd and TRO openingpressures

The in-situ (Pvo, Pvc) and surface (Psc, Pso) and thedome pressure (Pd) have been calculated at the valvetemperature

•

Pd is converted to its value at 60 oF – P dome at 60 oF column

• The Test Rack Opening TRO is derived from:

TRO= ( Pdome at 60 o

F - 14.65*R) /(1-R)


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EX 5 39Gaslift DesignSummary• Example of Gaslift design for a well that does not

flow naturally• Design Margins

– Casing-controlled valves –

Fluid-controlled valves• Sizing Facility

– Port size – Opening and closing pressures – Dome and Test Rack Opening pressure – Valve type selection

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Gas Lift Wellflo