Abstract:
A unique gas lift valve bellows assembly in which an internal piston incorporated within the bellows provides over travel prevention and over pressure protection during valve operation, independent of the set or operating gas pressures exerted on the gas lift valve. The piston separates a hydraulic damping reservoir in the interior convolutions of the bellows from the upper gas volume chamber. The piston travels a pre-set distance between two stops to provide a fluid dampened hydraulic balance across the bellows convolutions in both the open and closed positions of the valve. This results in a long lived bellows valve that can operate with any pressure up to the limits of the material, without overstressing the bellows.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     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.  
         [0003]     2. Description of Related Art  
         [0004]     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&#39;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.  
         [0005]     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.  
       SUMMARY OF THE INVENTION  
       [0006]     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.  
         [0007]     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.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     The apparatus of the invention is further described and explained in relation to the following figures wherein:  
         [0009]      FIG. 1  is a cross-sectional view of a typical wire line retrievable high pressure gas lift valve of the preferred embodiment;  
         [0010]      FIG. 2  is a cross sectional view of the upper chamber of the preferred embodiment illustrated in the fully extended position with the piston located at the lower travel stop;  
         [0011]      FIG. 3  is a cross sectional view of the upper chamber of the preferred embodiments from  FIG. 1 , illustrated in the fully contracted condition with the piston located at the upper travel stop.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0012]     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.  
         [0013]      FIG. 1  illustrates a gas lift valve  11  into which the present invention has been adapted. The valve  11  consists first of an upper chamber  1 , which includes a tail plug  2 , a sealing gasket  3 , a core valve  4 , and a set of external seals  34  employed to pack off the valve in the upper seal bore of an appropriate side pocket gas lift mandrel common to the industry and not illustrated herein. The upper chamber  1  is attached by means of a threaded connector or other suitable means to the improved metal bellows assembly  5  of the present invention, and is enclosed by a ported bellows housing  23 .  
         [0014]     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.  
         [0015]     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&#39;s lower travel stop  19 .  
         [0016]     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.  FIG. 2  will illustrate this condition. Compressed gas  38  from the casing-tubing annulus (not illustrated) injected from the surface wellhead provides a counteracting force on the external surface of the metal bellows  6 . When the force of compressed gas  38  is larger than the downward force upon the piston  10  of the compressed gas located in chamber  37 , the metal bellows  6  contract.  FIG. 3  will illustrate this condition.  
         [0017]     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 .  
         [0018]     As shown in  FIG. 1 , the gas lift valve  11  of the preferred embodiment further consists of a check valve assembly  24  common to the industry. Check valve assembly  24  comprises a nose cap  25 , and back check dart  26 , a spring  27 , a resilient seal  28 , a seal support washer  29 , and a back check adaptor  30 . The valve further consists of a lower packing adaptor  31 , in which is also located a seat  32  and a retaining ring  33  to capture the seat in the lower packing adaptor, and on which is located a set of external seals  34  employed to pack off the valve in the lower seal bore of an appropriate side pocket gas lift mandrel common to the industry and not illustrated herein.  
         [0019]      FIG. 2  illustrates the upper chamber  1  and improved metal bellows assembly  5  of the present invention with the bellows  6  in the fully extended condition and the internal piston  10  located against the lower travel stop  19 . Optionally, the lower travel stop  19  may be an adjustable screw to provide additional control over the distance that the piston  10  can move in internal sleeve  9 . The fully extended condition of the improved metal bellows assembly  5  is obtained when the pressure exerted upon the internal surfaces of the metal bellows  6  exceeds the pressure exerted upon the external surfaces of the metal bellows  6 .  
         [0020]     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 .  
         [0021]     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 .  
         [0022]      FIG. 3  illustrates the preferred embodiment of the present invention in the fully contracted condition, with the upper travel stop shoulder  22  of the internal ported sleeve  9  against the upper bellows adaptor  7  and the internal piston  10  located against the upper travel stop  18 . The fully contracted condition of the improved metal bellows assembly  5  is obtained when the pressure of injected gas  38  exerted upon the external surfaces of the metal bellows  6  exceeds the pressure exerted upon the internal surfaces of the metal bellows  6  from the compressed gas in chamber  36 . This would occur when the pressure of the injected gas  36  is raised above a certain threshold.  
         [0023]     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 .  
         [0024]     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.