Using Valve Performance Gas Lift Design Software

32nd Gas-Lift WorkshopThe Hague, The Netherlands

February 2 - 6, 2009

This presentation is the property of the author(s) and his/her/their company(ies).It may not be used for any purpose other than viewing by Workshop attendees without the expressed written permission of the author(s).

Using Valve Performance in

Gas Lift Design SoftwareTom Nations

Feb. 2 - 6, 2009 2009 Gas-Lift Workshop 2

Contents

• Definition of Valve Performance.• Differences between some of the available flow

correlations.• Valve Performance availability in gas lift design

software programs.• Using Valve Performance in Gas Lift Design.• What can happen if Valve Performance is not

considered.


Valve Performance

• Valve Performance is the determination of the actual flow rate through a gas lift valve at different combinations of Pvo, temperature and Piod.– Each make and model of gas lift valve is

somewhat different .– Bellows load rate and effective stem travel

must be determined.– Performance curves generated from dynamic

tests.


Valve Performance Methods

• VPCTM correlations.– Proprietary and are available only to members of the Valve

Performance Clearinghouse JIP.– Dynamic flow testing of many gas lift valves.– Predicted rates within 10% of actual performance.

• Winkler-Eads; T-C modified for the area open to flow.– Good for small ports but errors increase with port size.

• API Simplified, from API RP 11V2.– Requires knowledge of loadrate and flow coefficient.

• Thornhill-Craver.– Probably the most popular, but never intended to be used for

gas lift valves.– Can be off by as much as 200%, and should never be used for

live gas lift valves.


Gas Lift Valve Flow Performance


Valve Performance in software programs

• SNAP– Ryder Scott, LLC.

• WellFlow– Weatherford

• WinGLUE– AppSmiths

• PROSPER– Petroleum Experts


Using Valve Performance

• Typical gas lift graph showing injection pressure, flowing tubing pressure gradient and unloading valve locations.

• Valve set pressure and unloading lift gas rates will be shown on the following output text report.


Gas Lift Design Output Report


•Piod and tubing transfer pressures are used to calculate lift gas flow rates (Qgi).

•Thornhill-Craver predicts fully open square edge orifice rates.– grossly over estimating flow thru a gas lift valve.

•More injection pressure or lower Pvo may be required to make the valves flow sufficient lift gas rates to get the well unloaded.

Calculated lift gas flow rates


Top unloading valve

•147 mcfd of flow capacity is required to transfer to the next valve .•At the transfer pressure of 450 psi, the valve is actually closed.•A higher injection pressure or a lower Pvo is required.


Top Valve with 25 psi additional Piod pressure

• Same valve set at the same Test Rack opening pressure.– Only change is adding 25 psi additional casing pressure.– Now the valve flows 180 mcfd at 450 psi transfer pressure.


Top Valve with 25 psi reduction in Pvo

• A similar result can be obtained by changing the Pvo.– Pvo @ 60 was decreased by 25 psi.– The valve flows 200 mcfd at 450 psi tubing pressure with the

original design casing pressure of 1050 psi (1100 psi at depth).


Second Unloading Valve

•399 mcfd of flow capacity is required to transfer to the next valve .•At the transfer pressure of 655 psi, the valve is actually closed.•Again, more injection pressure or a lower Pvo is necessary.


Second Valve with 25 psi additional Piod pressure

• Same valve set at the same 1009 psi Pvo pressure.– Only change is adding 25 psi additional casing pressure.– Now the valve flows 191 mcfd at 555 psi tubing pressure.– Still not enough to match the required 399 mcfd.


Second Valve with 70 psi additional Piod pressure

• Same valve set at the same 1009 psi Pvo pressure.– 70 psi additional injection pressure yields 420 mcfd flow rate.

• But, if only 50 psi of additional injection pressure is available.– Also have to lower the Pvo as well as check flow at +50 psi.


Using Full Injection Pressure for Unloading

• You could use your full design injection pressure all but the top valve would flow considerably more lift gas.

• I recommend you design with less injection pressure than you actually have available at the wellhead (50-100 psi less) to avoid unloading problems.


Using Design Injection Pressure +50 psi

• Valve performance at full design injection pressure +50 psi.


Well would not Unload

• Unloading valves designed for 1400 psi injection pressure.• Well would only take lift gas sporadically.• Valve Performance was not considered in this design.


Valve Design Details

Input dialog box• Change the valve depths, types, port sizes, etc.• Change the Pvo60 values.• Adjust amount of additional injection pressure you wish to

evaluate.


Re-cap

• Definition of Valve Performance.• Differences between some of the available flow

correlations.• Valve Performance availability in gas lift design

software programs.• Using Valve Performance in Gas Lift Design.


•Do not rely on Thornhill-Craver flow rate calculations for gas lift design.•Gas Lift Design Software can be greatly improved by incorporating Valve Performance.•Without Valve Performance, the “black box” of a design program could easily result in a design that will have difficulty unloading.•Always use a design pressure 50-100 psi less than maximum injection pressure available at the well head.

– Especially important if your are using 1” gas lift valves.

Conclusions


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Using Valve Performance Gas Lift Design Software