Patent Application
20070227739
1. Field of the Invention
This invention relates generally to gas lift valves for the artificial production from oil and gas wells and, more particularly, to gas lift valves capable of operating at high differential pressures.
2. Description of Related Art
Gas lift valves have been used for many years to inject compressed gas into oil and gas wells to assist in the production of well fluids to the surface. The valves have evolved into devices in which a metal bellows, of a variety of sizes, converts pressure into movement. This allows the injected compressed gas to act upon the bellows to open the valve, and pass through a control mechanism into the fluid fed in from the well's producing zone into the well bore. As differential pressure is reduced on the bellows, the valve can close. Two types of gas lift valves use bellows. The first uses a non-gas charged, atmospheric bellows and requires a spring to close the valve mechanism. The other mechanism uses an internal gas charge, usually nitrogen, in the bellows and volume dome to provide the closing force for the valve. In both valve configurations, pressure differential on the bellows from the injected high pressure gas opens the valve mechanism.
In the case of the non-gas charged bellows, the atmospheric pressurized bellows is subjected to high differential pressures when the valve is installed in a well and exposed to high operating gas injection pressure. The nitrogen charged bellows is subject to high internal bellows pressure during setting and prior to installation. Once installed, the differential pressure across the bellows is less than in a non-gas charged bellows during operation of the valve. High differential pressure across a bellows during operation reduces the cycle life of the bellows. The existing gas lift valves and bellows are not designed to operate with set pressures or in operating pressures in excess of 2000 psig without severe failure risks. Some existing valve bellows do have some fluid and/or mechanical protection for overpressure due to operating pressures in the fill open position. However, none provide for protection from differential overpressure from the set pressure in the bellows.
The present invention comprises a gas-charged gas lift valve wherein the bellows of the gas lift valve are protected from high differential pressure. A piston is disposed in a central bore of a sleeve in the bellows. The piston separates a hydraulic damping reservoir in the interior convolutions of the bellows from the upper gas volume chamber containing the gas charge. The piston can only travel a pre-set distance in the internal bore between two stops. When operating pressure exerted on the bellows from the injected gas exceed the pressure of the gas charge in the upper gas chamber, the piston is pushed to contact the upper stop. More of the hydraulic dampening fluid is allowed to exit the interior of the bellow convolutions and move into the central bore of the internal sleeve. This allows the pressure from the injected gas to move the bellows into a contracted position to open the valve. Once the piston has reached the top position, the incompressible nature of the hydraulic fluid protects the bellows from any further increase in external pressure as well as further contraction due to that pressure. When the operating pressure of the injected gas drops below the pressure of the upper gas chamber, the gas in the upper gas chamber pushes the piston to the lower stop. This forces more of the hydraulic dampening fluid in the interior of the bellow convolutions, extending the bellows and closing the valve. Once the piston reaches the bottom position, the incompressible nature of the hydraulic fluid prevents the bellows from further extension and prevents a large pressure differential across the bellows.
The bellows design in the disclosed invention provides a fluid dampened hydraulic balance across the bellows convolutions in both the open and closed positions of the valve. It also preferably eliminates pressure differentials in excess of the natural spring rate of the bellows materials and any small compression resistance of the nitrogen charged gas in the dome/bellows volume. Since this new device prevents high differential pressure across the convolutions of the bellows, the valve can preferably be charged with any pressure up to the limits of the materials and can be run in any operating pressure up to the limits of the materials, without overstressing the bellows. This can provide a long lived bellows operation, approaching the life cycle ratings of the bellows manufacturer under low stressed conditions. The new bellows device can also preferably be retrofitted into existing gas lift valve configurations.
The apparatus of the invention is further described and explained in relation to the following figures wherein:
Various aspects and relationships of a preferred embodiment of the current invention will be described in the context of what is commonly known to the industry as a casing sensitive one inch wire line retrievable gas lift valve. It is within the scope of this patent to apply the present invention to other sizes and configurations of gas lift valves, both wire line retrievable and tubing retrievable gas lift valves and both injection pressure operated (IPO) or production pressure operated (PPO) valves.
The improved metal bellows assembly 5 of the present invention consists of a metal bellows 6, an upper bellows adaptor 7, a lower bellows adaptor 8, an internal ported sleeve 9, a piston 10, an adjustment screw 19, and a stem adaptor 12, to which is attached a stem 35. The metal bellows 6 is attached to the upper bellows adaptor 7 and the lower bellows adaptor 8 by any of the means of soldering, brazing, or welding to produce a strong hermetic seal between the metal bellows 6 and the upper and lower bellows adaptors 7, 8. The improved metal bellows assembly 5 is sealed to the upper chamber 1 by the use of O-rings 36 or any other suitable means.
The internal ported sleeve 9 has a small fluid port 13 through which hydraulic fluid is able to communicate from the annulus 15 created by the internal ported sleeve 9 and the interior of the metal bellows 6 to the internal seal bore 16 of the internal ported sleeve 9, and to act upon the piston 10. The piston 10 having external resilient seals 17 is located in the internal seal bore 16 of the internal ported sleeve 9 and is allowed to travel between the upper travel stop 18 and the lower travel stop 19. Lower travel stop 19 can optionally be an adjustment screw. The use of an adjustment screw as travel stop 19 allows the range of movement of piston 10 to be limited and thus the amount of extension of bellows 6. The internal ported sleeve 9 also has external seals 20 to seal it to the internal seal bore 21 of the upper bellows adaptor 7, an upper travel stop shoulder 22, and is allowed to travel within the upper adaptor 7 within travel limits imposed by the upper travel stop shoulder 22 and the piston's lower travel stop 19.
Upper chamber 1 contains compressed gas, typically nitrogen, in chamber 37 that exerts a downward force upon the piston 10. This pushes the piston 10 downward forcing the incompressible hydraulic fluid located in the internal seal bore 16 below the piston 10 in an external direction through the small fluid port 13 and into the annulus 15 created by the internal ported sleeve 9 and the interior surface of the metal bellows 6. Increased hydraulic fluid in annulus 15 causes the metal bellows 6 to extend.
The gas lift valve 11 of the preferred embodiment further comprises a stem adapter 12 secured to the lower bellows adapter 8. Stem 35 is secured in stem adapter 12 and is positioned proximate to seat 32. Upon extension of bellows 6, lower bellows adapter 8, and thus stem adapter 12, and stem 35 are translated toward seat 32. When bellows 6 are fully extended, stem 35 is seated in seat 32, thereby preventing injection gas 38 from passing through opening 40. This represents the ‘closed’ position of valve 11. Upon contraction of bellows 6, lower bellows adapter and thus stem adapter 12 and stem 35 are translated away from seat 32. This allows injection gas 38 to pass through opening 40 and out through nose cap 25 of valve 11. This represents the ‘open’ position of valve 11.
As shown in
The pressure of the compressed gas in the chamber 37 acts upon the area of the external seals 20 on the internal sleeve 9 and the external resilient seals 17 on the piston 10 to provide a downward force that tends to extend the metal bellows 6 and move the piston 10 downward. As the piston 10 travels downward in the internal seal bore 16 of the internal ported sleeve 9, it forces the hydraulic fluid in the internal seal bore 16 through the small fluid port 13 and into the annulus 15 created by the exterior of the internal ported sleeve 9 and the interior surface of the metal bellows 6. The pressure transferred to the internal surface of the metal bellows 6 by the displaced hydraulic fluid 14 causes the metal bellows 6 to extend. When the piston 10 travels to and is stopped by the lower travel stop 19 in this embodiment, no further hydraulic fluid 14 may be displaced into the annulus 15 created by the internal ported sleeve 9 and the interior surface of the metal bellows 6, thereby protecting the metal bellows 6 from any further increase in internal pressure, and thus also from any further extension or increased internal forces which would otherwise overstress the metal bellows 6.
When the improved metal bellows assembly 5 is in the fully extended position, less a small predetermined distance, and the piston 10 is within the same small predetermined distance from the lower travel stop 19, stem 35 first contacts and seals to the seat 32, thereby preventing injected gas 38 from passing through the valve 11. The inherent diametric flexibility of the metal bellows allows the piston 10 to continue until it contacts the lower travel stop 19. Once the piston 10 contacts the lower travel stop 19 any further extension of the metal bellows 6 is restricted due to the incompressibility of the contained hydraulic fluid in annulus 15.
When the pressure of the injected gas 38 is above the threshold, it forces the metal bellows 6 to contract, thus displacing the hydraulic fluid 14 from the annulus 15 created by the exterior of the internal ported sleeve 9 and the interior surface of the metal bellows 6 and into the internal seal bore 16 of the internal ported sleeve 9. The increased amount of hydraulic fluid 14 in the internal seal bore 16 forces the piston 10 in an upward direction, until it reaches the upward travel stop 18. The contraction of the metal bellows also moves internal sleeve 9 upward until a shoulder 22 on internal sleeve contacts upper bellows adapter 7. This raises stem 35 off of seat 32, thereby allowing injected gas 38 to pass through the valve. Upon reaching the upward travel stop 18, the piston 10 creates an impassable barrier for the hydraulic fluid in internal seal bore 16. The incompressible hydraulic fluid remaining in annulus 15 thereby protects the bellows from any further increase in external pressure, and thus also from any further contraction or increased external forces which would otherwise overstress the metal bellows 6.
The above descriptions of certain embodiments are made for the purposes of illustration only and are not intended to be limiting in any manner. Other alterations and modifications of the preferred embodiment will become apparent to those of ordinary skill in the art upon reading this disclosure, and it is intended that the scope of the invention disclosed herein be limited only by the broadest interpretation of the appended claims to which the inventor is legally entitled.
