6. Gas Lift - Analisis

Gas lift Modelling and Design Ex 6 1

Example 6

FloSystem User Course

Example 6

Gas lift Modelling and Design


Summary of Work-Flow for Gas Lift Design

• Check if well is naturally flowing

• Design with Deepest Point to get basic parameters of design

• Sensitivity to changing reservoir performance for bracketing envelope

• Select design parameters, valve type and set design margins

• Do Spacing calculations

• Do Sizing options - edit required changes

• Check un-loading at different conditions - use Re-Calc. Modify design if required

• Predict performance with real valves installed


Data Preparation: Reservoir Control

• File Example6.wfl

• Black Oil, Test Point PI Entry, Vertical Well


Reservoir Control: Oil Fluid parameters

• 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.


Reservoir Control: Inflow Performance

• Test Data : BHFP 1800 psia: 7200 stb/day

• Pres 3600 psia, Tres 190 oF


Inflow Performance: IPR Model

• Straight Line, Vogel, Norm Pseudo Pressure

Plot Inflow Curve


Inflow Performance:IPR Plot

• Comparative Plot for Report Purposes, showing changing performance below Pb

• Choose Norm. Pseudo Pressure


Data Preparation: Well Deviation

• Enter Deviation Data (survey)

• Last Entry to be Mid-Perf depth


Data Preparation: Equipment Data

• Install Completion as shown


Analysis: Natural Flow Performance

• Operating Point Calculation


Natural Flow Performance: Inflow/Outflow Plot

• No flow without artificial lift


G/L Design: Base Case Design Parameters

• Gaslift Supply Volume

• Gas Supply Pressure

• Valve Differential Pressure

• Max. depth of Gas Injection

Note: max. depthset to bottom of 4.5”tubing

Note: max. depthset to bottom of 4.5”tubing


Gas Lift Base Case - Using Deepest Point of Injection

Note: Depth of Injection is output

Note: Depth of Injection is output


Gas Lift Design Parameter Sensitivity Analysis

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

• Sensitivity to CHP - 1000,1200,1400 psia


Results of Design Parameter Sensitivity Analysis

Note: PaybackRatio

Note: PaybackRatio


Full Results of Design Parameter Sens. Analysis

Note: Qgi more crucial than CHP, but both increasedepth of injection

Note: Qgi more crucial than CHP, but both increasedepth of injection


Reservoir Decline Sensitivity Analysis

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

• Reservoir Depleted 800 psi

• Increasing Watercut: 50% to 75% 90%

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

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

still using deepest point of injection


Reservoir Decline Sensitivity Analysis

Results

• Inj. Depth increases from 11052 to 13295 as Player drops for 50% water-cut

• Inj. Depth decreases by up to 391 ft as Fw increases (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 -try reducing the lift gas rate to 1 MMscf/day

• Note bracketing envelope 11000-13000 ft.


G/L Design: Casing Controlled Valves Spacing

• Go to Analysis - Gas Lift Design

• Design rate 4600 b/d from Deepest Point runs

• Deepest Injection 13000 ft. - enter margins


Design Margins

• Select Design - Gas lift valve locations now calculated.


Example Valve Spacing

Unloading Casing Pressure (include closing pressure margin)

Unloading Casing Pressure (include closing pressure margin)

Objective Tubing Pressure (does not include transfer pressure margins)

Objective Tubing Pressure (does not include transfer pressure margins)


Valve where Pc-Pt>Pdiff including transfer margins

Valve where Pc-Pt>Pdiff including transfer margins

Valve where Pc-Pt>Pdiff excluding transfer margins, ie operating condiditons

Valve where Pc-Pt>Pdiff excluding transfer margins, ie operating condiditons

Dummy mandrels (Inactive valves) down to max. depth

Dummy mandrels (Inactive valves) down to max. depth

- Output (at op. valve)- Design (to unload)

- Output (at op. valve)- Design (to unload)TerminologyTerminology


Accept Design

• To accept design OK from Gas Lift Valve Positioning - go to Data Preparation - Gas lift Data - gas lift valves now in place.

CHP Updated FromDesign


Casing- and Tubing-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


Casing- and Tubing-Controlled: orifice sizing

• Can edit pressures (eg, to include margins) and temperature from plot (red)

• Calculates if orifice in critical flow


Casing-Controlled: Dome Pressure Setting

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

• Calculates Surface Open Pressure, downhole Closing Pressure = PDome, Surface Closing Pressure, and Test Rack & setting pressure

• Check that upper valves will close at operating pressure for design valve operation

• Design valve defaults to orifice with Pop = Ptube + Pdiff


Casing-Controlled: Dome Pressure Setting - cont.

• Alternative method : specify P surface close and 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


G/l Design: Final Design Pressure/Depth

Example Fluid-Controlled Design

Example Fluid-Controlled Design

Increments to ensure fluid controlled valves will close

Increments to ensure fluid controlled valves will close


Fluid-controlled design - setting increments

Transfer pres margin

Margin at valve 1

Obj. tubing pressure

Increment per valve


Fluid-controlled Valves - Orifice Sizing

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

Pt close= objective tubing pressure+closing pressure margin+transfer closing pressure margin

• The calculation will under-size the orifice needed on throttling valves: consult Gas Lift Company supplying valves

Qgas

P tubing

P transfer

P close

P casing

Qgi actual

Qgi Tho.-Crav.


Fluid-controlled Valves - Orifice Sizing

• The casing pressure (Pcasing) is calculated by adding the valve differential pressure:

Pt close + valve differential pressure

• This will give the designer input for the spreadsheet Pt close and P casing– See previous terminology


Any Design: Check Un-loading at Other Conditions

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

• In these pessimistic cases, can eliminate Design Margins. Use Re-Calculate

Example with Qgi reduced to 1.5 and Qlreduced to 3000 bpd

Well not unloaded tooriginal design valve


Any Design: Check if Reservoir Fluid is Entering TubingAny Design: Check if Reservoir Fluid is Entering Tubing

Projected Kill Fluid Gradients

Projected Kill Fluid Gradients

At this valve, reservoir fluid will not enter tubing

At this valve, reservoir fluid will not enter tubing

Here, reservoir fluid will 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 for unloading ability check


Gaslift Design Performance - under Operating Conditions

• Decide on casing head pressure for operation

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

• Make Valves active/inactive in order to model change of dummy mandrels for real valves in future.

• Sensisitivity analysis for further completion design or for forecasting

• Performance Curves vs. Qgi for use in optimisation (eg FieldFlo)


Gaslift Design Performance - Operating Point

Effect of CHP on production - actual valves: more CHP => deeper valve => more production

Effect of CHP on production - actual valves: more CHP => deeper valve => more production


Gaslift Design Performance - Pressure Profiles

Effect of CHP on production-actual valves: more CHP => deeper valve => more product.

Effect of CHP on production-actual valves: more CHP => deeper valve => more product.

Operating valve = solid lineOperating valve = solid line


Summary of Work-Flow for Gas Lift Design

• Check if well is naturally flowing

• Design with Deepest Point to get basic parameters of design

• Sensitivity to changing reservoir performance for bracketing envelope

• Select design parameters, valve type and set design margins

• Do Spacing calculations

• Do Sizing options - edit required changes

• Check un-loading at different conditions - use Re-Calc. Modify design if required

• Predict performance with real valves installed

Documents

6. Gas Lift - Analisis