Abstract:
There is provided a method of gas lift having the steps of positioning a valve seat downhole in a gas well experiencing hydrostatic loading, the valve seat having a gas flow channel, and providing a valve closure movable between a closed position engaged with the valve seat to close the gas flow channel and an open position spaced from the valve seat permitted a flow of gas through the gas flow channel, the closure being biased by magnetic attraction to a normally closed position magnetically engaged with the valve seat, such that gas is only able to flow through gas flow channel when gas pressure is sufficient to move the closure to the open position by overcoming the magnetic attraction which maintains the closure in the closed position.

Description:
FIELD 
       [0001]    There is described a method of gas lift in wells experiencing hydrostatic loading and a gas lift system in accordance with the teachings of the method. 
       BACKGROUND 
       [0002]    Hydrostatic loading occurs in gas wells when gas velocity in a well diminishes to a point where it can no longer lift produced liquids to surface, resulting in low or no gas production. Plunger lift systems are commonly used to overcome hydrostatic loading. With plunger lift systems, a plunger cycles up and down as surface gas valves are opened and closed. The plunger lift system includes a bumper spring to absorb the energy of the falling plunger and a check valve that stops liquids in the production spring from falling back into the reservoir. The plunger acts as a close fitting piston which travels up and down the internal bore of the tubing string. There are also, valves on the surface well head that will open and close to control the plunger. When the well is determined to be loading, the surface valves are shut in. This causes the plunger to fall to the bottom of the tubing string and contact the bumper spring. When the plunger is resting on the bumper spring, there is a check valve in the bumper spring that stops any liquid in the tubing string from returning to the reservoir. Once it is determined that the reservoir has built up adequate pressure, the valves on surface are opened. This causes the built up gas pressure to force the plunger along with any liquid that has accumulated on top of the plunger to surface. Once the plunger reaches surface, gases are released, which then allows the plunger to return to the bottom of the tubing string to await a build-up of pressure that enables the cycle to be repeated. There will hereinafter be described a new method of gas lift, an innovative gas lift system and a gas lift plunger assembly. 
       SUMMARY 
       [0003]    According to a first aspect there is provided a method of gas lift which involves positioning a valve seat downhole in a gas well experiencing hydrostatic loading, the valve seat having a gas flow channel. A valve closure movable is between a closed position engaged with the valve seat to close the gas flow channel and an open position spaced from the valve seat permitting a flow of gas through the gas flow channel. The closure is biased by magnetic attraction to a normally closed position magnetically engaged with the valve seat, such that gas is only able to flow through gas flow channel when gas pressure is sufficient to move the closure to the open position by overcoming the magnetic attraction which maintains the closure in the closed position. 
         [0004]    It is preferred that the valve closure be configured to fall back from the open position into the closed position by force of gravity as gas pressure diminishes, rather than through the use of springs. 
         [0005]    In one embodiment, the valve seat is a plunger receiver; and the valve closure is a plunger in the gas well that magnetically engages the plunger receiver. The plunger remains engaged with the plunger receiver by magnetic attraction, with the plunger blocking gas flow to surface, until gas pressure builds sufficiently below the plunger to overcome the magnetic attraction and propel the plunger to surface. 
         [0006]    According to a second aspect there is provided a gas lift system which includes a gas well experiencing hydrostatic loading, a plunger receiver downhole in the gas well, and a plunger in the gas well that magnetically engages the plunger receiver. The plunger remains engaged with the plunger receiver by magnetic attraction, with the plunger blocking gas flow to surface, until gas pressure builds sufficiently below the plunger to overcome the magnetic attraction and propel the plunger to surface. 
         [0007]    According to a third aspect, there is provide a gas lift plunger assembly which includes a plunger receiver and a plunger that magnetically engages the plunger receiver by magnetic attraction until a force is exerted to overcome the magnetic attraction. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    These and other features will become more apparent from the following description in which reference is made to the appended drawings, the drawings are for the purpose of illustration only and are not intended to be in any way limiting, wherein: 
           [0009]      FIG. 1  is a side elevation view of a downhole valve assembly. 
           [0010]      FIG. 2  is a side elevation view, in section, of the downhole valve assembly of  FIG. 1 , with the valve closure in the closed position. 
           [0011]      FIG. 2A  is a detailed side elevation view, in section, of the valve closure illustrated in  FIG. 2 . 
           [0012]      FIG. 3  is a side elevation view, in section, of the downhole valve assembly of  FIG. 1 , with the valve closure in the open position. 
           [0013]      FIG. 3A  is a detailed side elevation view, in section, of the valve closure illustrated in  FIG. 3 . 
           [0014]      FIG. 4  is a side elevation view, in section, of bottom hole assembly having a plunger receiver serving as a valve seat and a travelling ball serving as a valve closure. 
           [0015]      FIG. 5  is a side elevation view, in section, of surface assembly showing gas escaping when the travelling ball has reached the surface assembly. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    A first embodiment is a gas lift assembly in the form of a downhole valve generally identified by reference numeral  10 , which will now be described with reference to  FIGS. 1 through 3 . A second embodiment is a gas lift assembly using a plunger generally identified by reference numeral  100 , which will now be described with reference to  FIGS. 4 and 5 . 
       Structure and Relationship of Parts of First Embodiment 
       [0017]    Referring to  FIG. 1  and  FIG. 2 , downhole valve  10  has a valve seat  12  with at least one gas flow channel  14 . A valve closure  16  is be movable between a closed position engaged with valve seat  12  to close gas flow channel  14  ( FIG. 2A ) and an open position with valve closure  16  spaced from valve seat  12  permitting a flow of gas through gas flow channel  14  ( FIG. 3A ). A first rare earth magnet  18  and a second rear earth magnet  20  are provided. When valve closure  16  engages valve seat  12 , magnets  18  and  20  hold valve closure  16  in the closed position by magnetic attraction. With this configuration, gas is only be able to flow through gas flow channel  14  when gas pressure was sufficient to move valve closure  16  to the open position by overcoming the magnetic attraction of magnets  18  and  20  which otherwise maintains valve closure  16  in the closed position. The configuration of downhole valve  10  can vary. The configuration selected for illustration has a tubular body  22 . There is a gas inflow port  24  that allows gas to flow into interior  21  of tubular body  22  and a gas outflow port  26  that allows gas to exit tubular body  22 . Valve seat  12  is positioned between gas inflow port  24  and gas outflow port  26 , so gas cannot flow from gas inflow port  24  to gas outflow port  26  when valve closure  16  is in the closed position. Gas flow channel  14  has an annular lip seal  28  that seals with valve closure  16  when valve closure  16  is engaged with valve seat  12 . Tubular body  22  has exterior annular seals  30  to prevent gas passing along an exterior  32  of tubular body  22 . Tubular body  22  has a first end  34  and a second end  36 . Magnet  18  is positioned at first  34 . Magnet  20  is mounted at a remote end  38  of a rod  40  that extends from valve closure  16  toward magnet  18 . In operation, downhole valve  10  does not cycle up and down the tubing string as would a plunger, it remains positioned at the bottom end of the tubing string engaged with the bottom hole nipple. Second end  36  of tubular body  22  has a fish neck connector  42 , so that tubular body  10  may be gripped to remove downhole valve  10  from the well for periodic servicing. Fish neck connector  42  is connected to tubular body  22  by means of rod  43 , that has a bumper spring  44  outside of it. Bumper spring  44  is used to absorb the energy of a falling plunger. Rod  43  travels downwards as bumper spring  44  collapses. The upward travel of rod  43  is limited by a stop  45  positioned at a remote end of rod  43 . 
       Operation 
       [0018]    In operation, downhole valve  10  is inserted into a gas well and falls down the tubing string until it rests at the bottom end of the tubing string engaged with the bottom hole nipple. Referring to  FIG. 1 , gas flow along exterior  32  of tubular body  22  of downhole valve  10  is precluded by the presence of exterior annular seals  30 . Referring to  FIGS. 2 and 3 , this leaves the only path that gas can flow to surface through gas flow channel  14  of valve seat  12 . Referring to  FIG. 2 , valve closure  16  falls by force of gravity into engagement with valve seat  12 . It is held in this closed position by an engagement between magnet  18  and magnet  20 . Gas flow channel  14  has annular seal  28  that seals against valve closure  16  when valve closure  16  is engaged with valve seat  12 . Referring to  FIG. 3 , when gas pressure exceeds the force of magnetic attraction of magnet  18  and magnet  20 , valve closure  16  is forced to an open position, allowing gas to flow through gas flow channel  14 . In operation, valve closure  16  will continually cycle between the open position of  FIG. 3  and the closed position of  FIG. 2 ; with valve closure  16  remaining in the closed position until the force of magnetic attraction holding it in the closed position is overcome by a buildup of gas pressure. 
         [0019]    It was subsequently realized that this concept could be incorporated into existing plunger equipment that cycles up and down, with a plunger receiver serving as the valve seat and a plunger serving as the valve closure. This second embodiment will now be further described with reference to  FIGS. 4 and 5 . 
       Structure and Relationship of Parts 
       [0020]    Referring to  FIG. 4 , there is illustrated a bottom hole assembly  40  of a plunger lift system. Referring to  FIG. 5 , there is illustrated a surface assembly  42  of a plunger lift system. The valve seat is a plunger receiver  46 , which is incorporated into bottom hole assembly  40 . Bottom hole assembly  40  is positioned at the bottom end of tubing string  100  engaged with bottom hole nipple  102 . Bottom hole assembly  40  has a tubular body  48  with an interior surface  50  and an exterior surface  52 . Exterior seals  54  are positioned on exterior surface  52  and prevent gas from passing between exterior surface  52  and bottom hole nipple  102 . Plunger receiver  46  (the valve seat) is positioned at an upper end of a hollow rod  56 . Interior surface  50  of tubular body  48  has interior seals  58  that prevent gas from passing between interior surface  50  and hollow rod  56 . This leaves the only path that gas can pass is up internal gas passage  60  of hollow rod  56 . The upper portion of hollow rod  56 , has a bumper spring  62  outside of it. Bumper spring  62  is used to absorb the energy of a falling plunger. Hollow rod  56  travels downwards as bumper spring  62  collapses. Hollow rod  56  has upper stop shoulders  64  and lower stop shoulders  66 . The downward travel of hollow rod  56  is limited by upper stop shoulders  64 . The upward travel of hollow rod  56  is limited by lower stop shoulders  66 . Plunger receiver  46  (the valve seat) has a rare earth magnet  68 . 
         [0021]    The plunger system chosen for illustration is known as a “two piece” plunger system. The first piece is a tubular body  70 . The second piece is a travelling ball  72 . Travelling ball  72  magnetically engages plunger receiver  46 . Travelling ball  72  remains engaged with plunger receiver  46  by force of magnetic attraction blocking gas flow through gas passage  60  of hollow rod  56  until gas pressure builds sufficiently below travelling ball  72  to overcome the magnetic attraction and propel travelling ball to surface. 
         [0022]    Referring to  FIG. 5 , surface assembly  42  has a gas flow passage  74  for receiving the gas. It also has a cavity into which tubular body  70  is received and a trip valve rod  76  which separates travelling ball  72  from tubular body  70  at surface. 
       Operation 
       [0023]    Travelling ball  72  is held in place on plunger receiver  46  by magnet  68 . This allows the reservoir pressure to build up to a point that it overcomes the magnetic force and releases travelling ball  72 , allowing the plunger including travelling ball  72  and tubular body  70  to travel to surface. Magnet  68  directly induces a pressure differential between the reservoir and the inside of the tubing string. This embodiment can be incorporated in any plunger style. Some plunger lift styles but not limited to are/standard plungers/flow through plungers/bypass plungers/two piece plungers. In operation this plunger assembly is held in place at the bottom of the tubing string magnetically. The plunger seals the tubing string eliminating any gas by passing the plunger as long as the magnet is holding the plunger in place. When the reservoir pressure builds up to the point that the pressure differential can overcome the magnetic attraction then the plunger is free to travel up the inside of the tubing string to surface. Once the assembly reaches surface the gas is released. The manner of releasing the gas depends upon the plunger style. In the illustrated embodiment, there is a gas flow passage  74 . There is also a trip valve rod  76  that separates the plunger components and allows the plunger to return to the bottom of the tubing string once gas pressure is released via gas flow passage  74 . Once the plunger reaches the bottom of the tubing string, magnet  68  holds travelling ball  72  to plunger receiver  46  at the bottom of the well bore awaiting a reservoir pressure build up to repeat the cycle. 
         [0024]    The preferred approach is to use two magnets. However, it will be appreciated that the functions described could also be accomplished with a single magnet in combination with a second component made of a metal that reacts to the single magnet to create a desired magnetic attraction force. It will also be appreciated that the force of magnetic attraction can be varied through the selection of powers of the magnet or by adjusting the magnet clearance or by the number of magnets that are used. 
         [0025]    In this patent document, the word “comprising” is used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. A reference to an element by the indefinite article “a” does not exclude the possibility that more than one of the element is present, unless the context clearly requires that there be one and only one of the elements. 
         [0026]    The scope of the claims should not be limited by the illustrated embodiments set forth as examples, but should be given the broadest interpretation consistent with a purposive construction of the claims in view of the description as a whole.