6. Gas Lift - Analisis

7/16/2019 6. Gas Lift - Analisis

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Gas lift Modelling and Design Ex 61

Example 6

FloSystem User CourseExample 6

Gas lift Modelling and Design


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Summary of Work-Flowfor Gas Lift Design

Check if well is naturally flowing

Design with Deepest Poin tto get basicparameters of design

Sensitivity to changing reservoir performancefor bracketing envelope

Select design parameters, valve type and setdesign margins

Do Spacing calculations Do Sizing options - edit required changes

Check un-loading at different conditions - useRe-Calc. Modify design if required

Predict performance with real valves installed


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Data Preparation: ReservoirControl

File Example6.wfl

Black Oil, Test Point PI Entry, Vertical Well


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Reservoir Control: Oil Fluidparameters

35 API, 0.65 Gas Gravity, 300 scf/bbl GOR

50% w.c, 70,000 ppm salinity

Match any known data - in this case untuned

PVT correlations will be used.


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Reservoir Control: InflowPerformance

Test Data : BHFP 1800 psia: 7200 stb/day

Pres 3600 psia, Tres 190 oF


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Inflow Performance: IPRModel

Straight Line, Vogel, Norm Pseudo Pressure

Plot Inflow Curve


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Inflow Performance:IPR Plot

Comparative Plot for Report Purposes,showing changing performance below Pb

Choose Norm. Pseudo Pressure


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Data Preparation: WellDeviation

Enter Deviation Data (survey)

Last Entry to be Mid-Perf depth


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Data Preparation: EquipmentData

Install Completion as shown


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Analysis: Natural FlowPerformance

Operating Point Calculation


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Natural Flow Performance:Inflow/Outflow Plot

No flow without artificial lift


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G/L Design: Base CaseDesign Parameters

Gaslift Supply Volume

Gas Supply Pressure

Valve Differential Pressure

Max. depth of Gas Injection

Note: max. depthset to bottom of 4.5

tubing


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Gas Lift Base Case - UsingDeepest Point of Injection

Note: Depth of

Injection is output


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Gas Lift Design ParameterSensitivity Analysis

Sensivity to Qgi - 1,2,3 and 4 MMscf/day

Sensitivity to CHP - 1000,1200,1400 psia


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Results of Design ParameterSensitivity Analysis

Note:

Payback

Ratio


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Full Results of DesignParameter Sens. Analysis

Note: Qgi more

crucial than CHP,

but both increase

depth of injection

Depth of injection vs Qgi

7000

8000

9000

10000

11000

12000

13000

14000

0 1 2 3 4

1000

1200

1400


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Reservoir Decline SensitivityAnalysis

Target Gas Lift CHP 1200 psia, Qgi 2.5MMscf/day

Reservoir Depleted 800 psi

Increasing Watercut: 50% to 75% 90%

Set Qgi to 2.5 MMscf/day and CHP to 1200psia.

Run a sensistivity analysis with layerpressures of 3600 and 2800 psia forsensitivity 1 and water-cuts of 50,75 and 90%for sensitivity 2.

still using deepest

point of injection


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Reservoir Decline SensitivityAnalysis

Results

Inj. Depth increases from 11052 to 13295 asPlayerdrops for 50% water-cut

Inj. Depth decreases by up to 391 ft as Fwincreases (for less Qgi, effect is more)

depth at 50% vs 90% for Pl=2800

If less gas in future then the injection point

will move upwards more severely -tryreducing the lift gas rate to 1 MMscf/day

Note bracketing envelope 11000-13000 ft.


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G/L Design: CasingControlled Valves Spacing

Go to Analysis - Gas L if t Design

Design rate 4600 b/d from Deepest Point runs

Deepest Injection 13000 ft. - enter margins


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Design Margins

Select Design -Gas lift valve locations nowcalculated.


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Example Valve Spacing

Unloading Casing

Pressure(include closing

pressure margin)

Objective Tubing Pressure

(does not include transfer

pressure margins)

Output (at op valve)


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Valve where Pc-Pt>Pdiffincluding transfer margins

Valve where Pc-Pt>Pdiffexcluding transfer margins,

ie operating condiditons

Dummy mandrels (Inactive

valves) down to max. depth

- Output (at op. valve)

- Design (to unload)Terminology


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Accept Design

To accept design OK from Gas Lif t ValvePosi t ioning- go to Data Preparation - Gas li f tData- gas lift valves now in place.

CHP Updated From

Design


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Casing- andTubing-Controlled: orifice sizing

Can edit gas rate (red) Can edit Valve Manufacturer and Model.

(yellow)

Calculates orifice size: can over-write (green)

NOTE: USES THORNHILL-CRAVER ONLY


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Casing- andTubing-Controlled: orifice sizing

Can edit pressures (eg, to inc lude margins)and temperature from plot (red)

Calculates if orifice in critical flow


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Casing-Controlled: DomePressure Setting

Input valve model required (catalogue). WellFlo will sizeit so that R is approximately 0.2

Calculates Surface Open Pressure, downhole ClosingPressure = PDome, Surface Closing Pressure, and TestRack & setting pressure

Check that upper valves will close at operating pressurefordesign valveoperation

Design valve defaultsto orifice with Pop = Ptube + Pdiff


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Casing-Controlled: DomePressure Setting - cont.

Alternative method : specify P surface closeand calculate the operating pressures(ensures that a pressure drop will be seen as

each valve closes)

Note: If spring valve type, no temperature

correction is made to the dome and test rack

pressures


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G/l Design: Final DesignPressure/Depth

Example Fluid-

Controlled Design

Increments to ensure fluid

controlled valves will close


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Fluid-controlled design -setting increments

Transfer pres margin

Margin at valve 1

Obj. tubing pressure

Increment per valve


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Fluid-controlled Valves -Orifice Sizing

For Orifice Sizing need to over write closingpressure (Pt close) by adding P closing transfer margin

Pt close= ob ject ive tubing p ressure+closing pressuremargin+transferclosing pressure margin

The calculation will under-size the orificeneeded on throttling valves: consult Gas LiftCompany supplying valves

Qgas

P tubing

P transfer

P close

P casing

Qgi actual

Qgi Tho.-Crav.


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Fluid-controlled Valves -Orifice Sizing

The casing pressure (Pcasing) is calculatedby adding the valve dif ferent ial pressu re:

Pt clos e + valve dif ferent ial pressure This will give the designer input for the

spreadsheet Pt close and P casing

See previous terminology


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Any Design: Check Un-loading at Other Conditions

Verify un-loading at other conditions,especially lower Qgi (if full gas not able to beinjected), higher water cut etc.

In these pessimistic cases, can eliminateDesign Margins . Use Re-Calculate

Example with Qgi

reduced to 1.5 and Qlreduced to 3000 bpd

Well not unloaded to

original design valve

Any Design: Check if Reservoir Use any spreadsheet - input


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Any Design: Check if ReservoirFluid is Entering Tubing

Projected Kill

Fluid Gradients

At this valve, reservoir fluid

will not enter tubing

Here, reservoir fluid

will enter tubing

Use any spreadsheet input

Ptransfer, TVD and TVD res., and

kill fluid gradient. Check if

Pkill fluid < Pres at datum.

See previous slide forunloading ability check


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Gaslift Design Performance -under Operating Conditions

Decide on casing head pressure for operation

Do Not use Forced Gas Entry: WellFlo willcalculate which valve will operate

Make Valves active/inactivein order to modelchange of dummy mandrels for real valves infuture.

Sensisitivity analysis for further completiondesign or for forecasting

Performance Curves vs. Qgi for use inoptimisation (eg FieldFlo)


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Gaslift Design Performance -Operating Point

Effect of CHP on production - actual valves:

more CHP => deeper valve => more production


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Gaslift Design Performance -Pressure Profiles

Effect of CHP on production-

actual valves: more CHP =>

deeper valve => more product.

Operating valve = solid line


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Summary of Work-Flowfor Gas Lift Design

Check if well is naturally flowing

Design with Deepest Poin tto get basicparameters of design

Sensitivity to changing reservoir performancefor bracketing envelope

Select design parameters, valve type and setdesign margins

Do Spacing calculations Do Sizing options - edit required changes

Check un-loading at different conditions - useRe-Calc. Modify design if required

P di t f ith l l i t ll d

6. Gas Lift - Analisis

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