33 rd Gas-Lift Workshop Houston, Texas, USA February 1-5, 2010 VPC History and Summary of Work Ken Decker Decker Technology, Inc. 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).
Contents History Current Status Summary of Work Testing Procedures Correlation Development Anomalies Summary 2010 Gas-Lift Workshop 2
History Publication of API 11V2 in 1995 Joint Industry Project (JIP) formed with Decker Technology, Inc. as administrator in 1996 Chevron Petroleum Company Conoco Edinburgh Petroleum Services Exxon Production Research Marathon Oil Company Shell International 2010 Gas-Lift Workshop 3
History 1 year contract t with each member, option to be renewed each year Members elected which valves to test Decker Technology Inc. performed all testing Data, VPC program and database supplied to each member at end of year Annual meeting held each year to select next year s test valves 2010 Gas-Lift Workshop 4
History First meeting of VPC held in 1996 in Denver Models used existing TUALP data Elected to test Merla N-15R, LN-20R, HES Nova, McMurry VR-STD, and JR-FOP in 1997 Testing and meeting have been held every year since 1996 First tests conducted at SwRI Later tests conducted at Weatherford 2010 Gas-Lift Workshop 5
Current Status The VPC has 8 members Chevron Texaco Conoco Phillips Exxon Mobil Petronas Petroleum Technology Company Saudi Aramco Shell International Exploration & Production Weatherford 2010 Gas-Lift Workshop 6
Current Status VPC program and source code for model correlations are available free of charge with perpetual license Database remains proprietary to VPC members Many ygas lift software vendors now have VPC correlations built into the code Activation of database is through the VPC with a license fee of $1300 per port size License is perpetual with no maintenance fees 2010 Gas-Lift Workshop 7
Current Status Full database available for initiation iti fee of $15K plus first year s membership fee. Members receive software support. License holders receive free support for the first year. VPC program is updated as required for new correlations but existing correlations have been sufficient for many years. New valves are added to the VPC program by updating the database. 2010 Gas-Lift Workshop 8
Summary of Work 46 valves tested t to date This includes most major valves used in the world A few of the new high pressure valves also tested A few of the new barrier valves have been tested 4 additional valves will be tested this year Cycle testing performed on one IPO valve Erosion testing performed on several valves 2010 Gas-Lift Workshop 9
Testing Procedures API 11V2 used as testing ti method Stem travel and load rate tests Flow Coefficient Tests Dynamic Tests Flow tests are conducted on API certified test stand Data is collected electronically Correlations built by Decker Technology, Inc. 2010 Gas-Lift Workshop 10
Correlation Development Stem travel and Load rate tests t Load rate tested at three pressures Load rate is pressure dependent Load rate computed for Pvc of 800 psig Linear equation developed to predict load rate at other pressures Database contains load rate at Pvc = 800 and the slope of the load rate for other pressures VPC program calculates Ptro at temperature and then calculates load rate for that Ptro. 2010 Gas-Lift Workshop 11
Correlation Development Flow coefficient i tests t performed at 5 stem travels Flow coefficient (Cv) and critical pressure ratio (Xt) extracted from each test Cv and Xt are plotted as a function of stem travel Third order polynomial equation is fitted to the plot Coefficients of polynomial equation are entered into database 2010 Gas-Lift Workshop 12
Correlation Development Static ti force balance equation is used to determine the stem travel at each data point of dynamic tests Pd*Ab + Rl*Ab*dx = P1(Ab-Ap) + P2*Ap Cv extracted from each data point of dynamic tests Cv polynomial equation used to determine actual stem travel during the test 2010 Gas-Lift Workshop 13
Correlation Development The stem travel calculated l from the static ti force balance equation usually does not match the actual stem travel calculated from the dynamic tests. There are several reasons for this Force balance equation assumes P2 acts on full area of port. This is not true. Force balance equation assumes the measured downstream pressure is the pressure acting on the full area of the port. This is not true. 2010 Gas-Lift Workshop 14
Correlation Development A correlation is required to compute the actual stem travel as a function of the static stem travel. Once this correlation is established, the static force balance equation can be used to predict the actual stem travel. The correlation is used to find the actual stem travel. The Cv polynomial equation is then used to find the actual Cv. The flow rate equation is then invoked to determine the actual flow rate. 2010 Gas-Lift Workshop 15
Correlation Development The correlation is used to plot a performance curve. This curve is compared to the actual test data. The correlation is fine tuned until the difference between the correlation and the actual test data is less than +/-10% for the full range of tested pressures. The correlation coefficients are entered into the database. A second database coefficient is used to select the proper correlation. 2010 Gas-Lift Workshop 16
Correlation Development The VPC program is run with the new correlation for the particular valve and port size at the same pressure and temperature conditions that existed during the dynamic tests. These plots are compared to the dynamic test data. When the VPC plots are within +/-10% of the actual test data, the new database is released to the VPC members. 2010 Gas-Lift Workshop 17
Correlation Development A gas lift valve is a mechanical device it obeys the laws of physics in spite of attempts to attribute a perceived flow performance. The correlation development process applies the law of physics albeit with a correlation. It is the best we have to date. It is MUCH better than the Thornhill-Craver equation we have been using. It works! Use it! 2010 Gas-Lift Workshop 18
Anomalies 1i inch valves do NOT perform the same way 1-1/2 11/2 valves perform! 1 inch valves have much higher load rates and hence much lower stem travel for the same pressure conditions. The ratio of port size to bellows area is vastly different. Do you use the same design technique with 1 inch valves as you do with 1-1/2 inch valves? Current gas lift design methods do not make this distinction. Maybe you should. 2010 Gas-Lift Workshop 19
Anomalies 2010 Gas-Lift Workshop 20
Anomalies Do IPO valves throttle ttl to a closed position? It depends are you using a 1 inch valve or a 1-1/2 valve? What size port is it? In a 1-1/2 IPO valve, if the port is 3/16 or less, it may not throttle. In a 1 IPO valve, anything more than a 10/64ths port will throttle to a closed position. 2010 Gas-Lift Workshop 21
Throttling 2010 Gas-Lift Workshop 22
Throttling 2010 Gas-Lift Workshop 23
Anomalies PPO valves are supposed to be injection pressure independent. This is not true! PPO valves with cross-over over ports can become IPO valves! Critical flow occurs at the cross-over ports and the bellow is isolated from downstream pressure! When this occurs (usually at the top or second valve), the only way to close them is to drop injection pressure! The newer PPO valves with smiley face ports are truly PPO valves. They will close! 2010 Gas-Lift Workshop 24
PPO Valve Performance 2010 Gas-Lift Workshop 25
Anomalies Does an IPO valve with a downstream choke flow more or less than without a choke? It depends A 1 inch IPO with port sizes greater than 3/16 with a downstream choke will flow more than without a choke. Counter intuitive iti but true. A 1-1/2 IPO with a downstream choke will flow about the same or less than without a choke. 2010 Gas-Lift Workshop 26
IPO Valves w/ Downstream Choke 2010 Gas-Lift Workshop 27
IPO w/ Downstream Choke 2010 Gas-Lift Workshop 28
Anomalies Constant t flow valves. These are IPO valves with an upstream choke. The idea is to create a higher pressure on the bellows thus causing more stem travel. Does it work? It depends If it is a 1 inch valve with a port greater than 3/16, there is a benefit. If it is a 1-1/2 valve the results are mixed. 2010 Gas-Lift Workshop 29
Constant Flow Valves 2010 Gas-Lift Workshop 30
Summary The VPC correlations are usually within +/-10% of actual performance. Much better than Thornhill-Craver. 1 inch valves are not the same as 1-1/2 valves. Performance of valves is condition dependant. Upstream chokes, down stream chokes, valve size, port size, pressure conditions It can get pretty confusing. Don t assume! 2010 Gas-Lift Workshop 31
Conclusion Thank you. I hope this presentation ti has inspired i you to ask a few more questions before sending that design to the field. Questions? 2010 Gas-Lift Workshop 32
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