VPC Testing Procedures

1. VPC Testing Procedures • VPC uses the API 11V2 RP to test valves. This includes…. • Loadrate tests • Flow Coefficient tests • Dynamic Tests

2. Gaslift Valve Basics Typical IPO and PPO valves

3. Static vs Dynamic Force Balance • The static force balance equation is good ONLY when the valve is closed or full open. It can not be used to accurately predict the stem position when the valve is open and flowing. • When the valve is open and flowing, the stem will be in the flow path and the downstream pressure acting on the stem will not be the same as the tubing pressure….and the area of the stem effected by this pressure will not be the same as the area of the port. • Normally, the stem is closer to the seat than predicted by the static force balance equation.

4. Dynamic Force Balance Equation • For IPO valves, the dynamic force balance equation is….. • Pcf*(Ab-Av) + Pv*Av = Pdome*Ab + Blr*dxs*Ab • For PPO valves, the dynamic force balance equation is… • Pcf*Av + Pv*(Ab-Av) = Pdome*Ab + Blr*dxs*Ab • Pv = Downstream pressure acting on stem • Av = Area of stem effected by downstream pressure

5. Loadrate • Loadrate is a measure of the valve stem’s resistance to movement. The nitrogen dome and bellows act like a spring. The pressure acting across the full area of the bellows required to compress the nitrogen and bellows is the loadrate. • Loadrate is one of the MOST important gaslift valve performance parameters. • Loadrates of a type of valve (for example the R-1) will be nearly constant for all newly manufactured valves. • Loadrates of used valves will usually be slightly less than for newly manufactured valves.

6. Typical Loadrate Test Data

7. Typical Loadrates of Gaslift Valves

8. Nitrogen vs Spring • Loadrates of nitrogen charged valves are a function of the set pressure. • Loadrates of spring loaded valves are nearly constant. • Typically, spring loaded valves have much higher loadrates than nitrogen charged valves therefore…for the same pressure conditions, nitrogen charged valves will come farther open than spring loaded valves.

9. Effective Stem Travel • Effective stem travel is the amount the stem can move away from the seat within the linear portion of the loadrate curve. • Effective stem travel is a function of set pressure for valves with internally charged bellows. The higher the set pressure, the lower the effective stem travel. • For externally charged bellows, the effective stem travel is constant regardless of set pressure.

10. Stem Travel for a Full Open Port

11. Bellows Stacking • Bellows which are designed to compress when the valve opens suffer from “bellows stacking”. • Bellows stacking occurs when the outer convolutions of the bellows come in contact with each other. When this happens, the loadrate increases dramatically. • Internally charged bellows set at high pressures cause the outer convolutions to balloon which limits the amount of effective stem travel. • Once lost, due to high set pressures, effective stem travel can not be recovered.

12. Flow Coefficients • Flow coefficients are a measure of the flow capacity of a valve and are a function of port size and stem travel. • The flow coefficient test also determines when the valve “chokes”. • Flow coefficients of valves are constant regardless of whether the valve is new or used.

13. Typical Flow Coefficient Curve

14. Vibration Dampening • Gaslift valves tend to “chatter” when throttling. The liquid fill in the dome is used to suppress the chatter. • The liquid fill is usually Silicon fluid. Silicon fluid if very temperature sensitive and expands at five times the rate of water. • Silicon fluid in the dome WILL increase the set pressure more than the normal temperature correction. • The more silicon fluid, the more the set pressure will increase. Don’t ignore this!

15. Silicon Fluid vs Set Pressure

16. VPC99 Flow Passage

17. VPC99 Flow Passage w/ Thornhill-Craver

18. Top Valve at a Range of Temps

19. Top Valve with Range of Injection Pressures

20. Troubleshooting Philosophy • All the gas injected into the annulus must come back through the tubing but… • The gas may not come back in the tubing at the same rate as injected so… • Annulus pressure will change to account for the different rates at which gas is injected at the surface and injected through the gaslift valves.

21. Troubleshooting Philosophy • First Step ~ Is the annulus pressure steady? If so, then the rate at which gas is injected at the surface is the same as the rate at which gas is injected through the valves and….. • Use the VPC program to find out where the gas is going based on the current operating conditions.

22. Troubleshooting Philosophy • If the injection pressure is cycling, then the rate at which gas is being injected at the surface does not match the rate at which gas is being injected through the valves. • Valves are opening and closing or, in the case of an orifice, the differential pressure is changing and the orifice could go on backcheck.

23. Troubleshooting Philosophy • In general, if the injection pressure is changing by less than 15 psig then multipointing is occurring where an upper valve is opening and closing but a lower valve is staying open. • If the injection pressure is changing by more than 15 psig then multiple valves are opening and closing simultaneously

24. Dynamic vs Static Gaslift • Most gaslift design programs are static. • They assume the annulus pressure changes as each lower valve is uncovered. This will happen only if the injection rate is matched to the flow rate through the valve. In most cases, the annulus pressure changes continuously during the unloading phase.