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BACKGROUND 
       [0001]    The invention generally relates to a gas lift valve. 
         [0002]    A well typically includes a production tubing string for purposes of communicating well fluid to a surface of the well through a central passageway of the string. Due to its weight, the column of well fluid that is present in the production tubing string may suppress the rate at which the well fluid is produced from the formation. More specifically, the column of well fluid inside the production tubing string exerts a hydrostatic pressure that increases with well depth. Near a particular producing formation, the hydrostatic pressure may be significant enough to substantially impede the rate at which the well fluid is produced. 
         [0003]    For purposes of reducing the hydrostatic pressure and thus, enhancing the rate at which fluid is produced, an artificial-lift technique may be employed. One such technique involves at various downhole points in the well, injecting gas into the central passageway of the production tubing string to lift the well fluid in the string. The injected gas, which is lighter than the well fluid displaces some amount of well fluid in the string. The displacement of the well fluid with the lighter gas reduces the hydrostatic pressure inside the production tubing string and allows the reservoir fluid to enter the wellbore at a higher flow rate. The gas to be injected into the production tubing string typically is conveyed downhole via the annulus (the annular space surrounding the string) and enters the string through one or more gas lift valves. 
       SUMMARY 
       [0004]    In one example, a gas lift valve assembly includes a housing that includes a first passageway that is substantially concentric with the central passageway of a string to communicate well fluid and a second passageway that is eccentrically disposed with respect to the central passageway to communicate a second fluid to lift the well fluid. The gas lift valve assembly includes a valve that is disposed in the second passageway and includes a ball valve to regulate communication of the second fluid. 
         [0005]    In another example, a method includes providing a gas lift valve that includes a ball valve element and operating the ball valve element to regulate fluid communication through the gas lift valve. 
         [0006]    In yet another example, a system includes a string that includes a central passageway to communicate well fluid to the surface and gas lift valve assemblies. At least one of the gas lift valve assemblies includes a ball valve to regulate communication of a gas lift fluid into the central passageway of the string. 
         [0007]    Advantages and other features of the invention will become apparent from the following drawing, description and claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0008]      FIG. 1  is a schematic diagram of a well according to an example. 
           [0009]      FIG. 2  is a schematic diagram of a gas lift valve assembly according to an example. 
           [0010]      FIG. 3  is a flow diagram depicting an artificial lift technique according to an example. 
           [0011]      FIG. 4  is a perspective view of a ball valve according to an example. 
           [0012]      FIG. 5  is a cross-sectional view of the gas lift valve of  FIG. 2  according to an example. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    In the following description, numerous details are set forth to provide an understanding of the present invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these details and that numerous variations or modifications from the described embodiments are possible. 
         [0014]    As used here, the terms “above” and “below”; “up” and “down”; “upper” and “lower”; “upwardly” and “downwardly”; and other like terms indicating relative positions above or below a given point or element are used in this description to more clearly describe some embodiments of the invention. However, when applied to equipment and methods for use in wells that are deviated or horizontal, such terms may refer to a left to right, right to left, or diagonal relationship as appropriate. 
         [0015]    Referring to  FIG. 1 , a subterranean well  10  includes a wellbore  11  that extends downhole into one or more subterranean formations. As depicted in  FIG. 1  for purposes of example, the wellbore  11  is vertical. However, the techniques and systems that are disclosed herein may likewise be applied to lateral or highly deviated wells. Additionally, the wellbore  11  may or may not be cased by a casing string  12 , which is depicted in  FIG. 1 . Furthermore, the well  10  may be a terrestrial subterranean well or may be a subset well, as many variations are contemplated and are within the scope of the appended claims. 
         [0016]    As depicted in  FIG. 1 , a production tubing string  14  extends downhole into the wellbore  11 . The production tubing string  14  communicates well fluid to the surface of the well. For purposes of enhancing the rate at which well fluid is produced, an artificial-lift technique may be employed in which a lifting gas (provided by a surface-disposed lift gas source  12 , for example) is injected into the production tubing string  14  to displace well fluid in the string  14  with the lighter gas to enhance the production of the well fluid. In general, the gas is communicated downhole via an annulus  15  of the well  10  and enters the production tubing string  14  at various controlled access points along the string  14 . 
         [0017]    More specifically, as an example, the production tubing string  14  may include several side pocket gas lift mandrels  16  (gas lift mandrels  16   a ,  16   b  and  16   c , being depicted as examples in  FIG. 1 ), which contain flow control devices to control the communication of gas from the annulus  15  into the central passageway of the string  14 . More specifically, each of the gas lift mandrels  16  includes an associated gas lift valve  18  (gas lift valves  18   a ,  18   b  and  18   c , being depicted as examples in  FIG. 1 ) for purposes of establishing one way fluid communication paths from the annulus  15  into the central passageway of the production tubing string  14 . 
         [0018]    As described herein, the gas lift valves  18  are injection pressure operated (IPO) valves. In general, an IPO valve opens when the annulus pressure exceeds the production tubing string pressure by a certain threshold. The pressure thresholds of the gas lift valves  18  may be separately configured, which permits the gas lift valves  18  to be opened in a certain sequence. It is noted that the production tubing string  18  may contain more or less than the three gas lift valves  18  that are depicted in  FIG. 1 . Furthermore, the production tubing string  14  may contain one or more gas lift valves that have designs different than the design of the gas lift valve  18 . 
         [0019]    As described herein, the gas lift valve  18  includes a ball valve  19 , which is constructed to be operated such that when the pressure of the annulus  15  near the gas lift valve  18  exceeds a certain threshold, the ball valve  19  opens to permit communication between the surrounding annulus and the central passageway of the production tubing string  14 . The ball valve  19  is further constructed to automatically close when the annulus pressure near the gas lift valve  18  decreases below the threshold. 
         [0020]    Due to the use of the ball valve  19  to control the flow through the valve  18 , the valve  18  may be used in a barrier application. As a comparison, a conventional gas lift valve may use a check dart-type valve element for purposes of preventing a reverse flow through the gas lift valve when closed. However, these valve elements may deform when the element is used over a relatively wide pressure range, and this deformation may cause leakage. As such, conventional gas lift valves may not be suitable for a barrier application, which needs to seal over a wide range of pressures. In contrast, the ball valve design is capable of sealing over a wide range of pressures and thus, is suitable for use as a barrier device. 
         [0021]    Referring to  FIG. 2  in conjunction with  FIG. 1 , as an example, the side pocket gas lift mandrel  16  is a sub, or assembly, of the production tubing string  14 , which houses the gas lift valve  18  and provides ports that permit communication between the annulus  15  and central passageway of the production tubing string  14 . The gas lift mandrel  16  includes a tubular housing  17  that contains a central passageway  35  that is concentric with the longitudinal passageway  120  of the mandrel  16  and forms a corresponding section of the central passageway of the production tubing string  14 . The housing  17  also includes a smaller diameter offset, or eccentrically-disposed, passageway  32  that is generally parallel with but is eccentric with respect to the longitudinal axis  120 . As depicted in  FIG. 2 , the gas lift valve  18  is disposed inside the eccentrically-disposed passageway  32 . 
         [0022]    As shown in  FIG. 2 , the passageways  32  and  35  are generally parallel to each other, and the housing  17  includes at least one radial port  36  to establish fluid communication between the longitudinal passageways  32  and  35  when the gas lift valve  18  is open. The side pocket mandrel  16  further includes one or more radial ports  38  for purposes of establishing communication between the annulus  15  and one or more inlet ports  58  of the gas lift valve  18 . In this regard, the gas lift valve  18  includes upper  60  and lower  61  seals (o-ring seals, v-ring seals or a combination of these seals, as non-limiting examples) that circumscribe the outer surface of the housing of the gas lift valve  18 . These seals contact the inner wall of the passageway  32  to form a sealed annular space for receiving fluid from the annulus  15 . 
         [0023]    In general, the gas lift valve  18  controls fluid communication between the annulus  15  and the central passageway of the production tubing string  14  in the following manner. As long as the annulus pressure is below a certain threshold, the ball valve  19  of the gas lift valve  18  remains closed to block fluid communication between the inlet port(s)  58  and an outlet port  52  of the gas lift valve  18 . Thus, when the ball valve  19  is closed, fluid communication does not occur through the gas lift valve  18 . When the annulus pressure exceeds the threshold, as described further below, the ball valve  19  opens to permit fluid communication between the inlet port(s)  58  and the outlet port  52 . When the ball valve  19  is open, fluid thus is communicated between the annulus  15 , into the inlet port(s)  58 , through the ball valve  19 , through the outlet port  52 , through the port(s)  36  and into the central passageway of the production tubing string  14 . 
         [0024]    It is noted that the gas lift valve  18  may be installed and/or removed from the production tubing string  14  by a wireline operation (as a non-limiting example). In this regard, as a non-limiting example, the gas lift valve  18  may include a latch  62 , which is engageable by a tool at the end of a wireline for purposes of securing the gas lift valve  18  inside the passageway  32 , as well as releasing the gas lift valve  18  from the side pocket mandrel  16  for purposes of retrieving the valve  18  to the surface of the well  10 . 
         [0025]    Referring to  FIG. 3 , in accordance with embodiments of the invention, a technique  80  that is depicted in  FIG. 3  may be used in conjunction with a gas lift valve. Pursuant to the technique  80 , the gas lift valve is run into a well, pursuant to block  82 . The annulus pressure is regulated, pursuant to block  84 , to selectively open and close a ball valve of the gas lift valve to control fluid communication through the gas lift valve. 
         [0026]    Referring to  FIG. 4 , as a non-limiting example of a possible design for the ball valve  19 , the valve  19  may include a ball element  100  that rotates about an axis  102  between open and closed positions. In this regard, the axis  102  is generally transverse to the longitudinal axis  120  of the production tubing string  14 , and pivot points extend from the ball element  100  into corresponding recesses of the housing of the ball valve  19  to confine the ball element  100  to rotate about the axis  102 . 
         [0027]    The ball element  100  includes a central passageway  104 , which is aligned with the central passageway of the production tubing string  14  in the open state of the ball valve  19 . In the closed state of the ball valve  19 , the ball element  100  is rotated so that the passageway  104  is no longer aligned with the central passageway of the production tubing string  14 , but rather, for this orientation of the element  100 , the solid portion of the element  100  blocks fluid communication through the valve  19 . 
         [0028]    The angular orientation of the ball element  100  about the axis  102  is controlled by a yoke  106  and a pin  110 . The pin  110  is located near a lower end of the yoke  106  and resides in a slot  105  of the ball element  100 . In general, the free end of the pin  110  resides in a longitudinal slot inside the housing of the gas lift valve  18  and is confined by the slot to move along the longitudinal axis  120  with the longitudinal translation of the yoke  106 . Due to the eccentric positioning of the pin  110  with respect to the axis  102  of the ball element  100 , upward movement of the yoke  106  causes the ball element  100  to rotate about the axis  102  to its closed position. Conversely, downward travel of the yoke  106  causes an opposite rotation of the ball element  100  for purposes of returning the ball element  100  to its open position (as depicted in  FIG. 4 ). As also depicted in  FIG. 4 , in general, the yoke  106  includes a longitudinally extending operator  112  that is connected to an actuator (as further described below) for purposes of longitudinally translating the yoke  106  and thus, transitioning the ball valve  19  between its open and closed states. 
         [0029]      FIG. 5  depicts a non-limiting example of a possible implementation of the gas lift valve  18 . For this example, the actuator for the ball lift valve  19  includes a metal bellows diaphragm  150 . More specifically, the ball valve  19  is located inside an outer housing  130  of the gas lift valve  18 . The outer housing  130  includes a longitudinal slot in which the pin  110  slides and also includes the radial ports  58  that are constructed to receive well fluid from the annulus  15  (see  FIGS. 1 and 2 , for example). The ball valve  19  controls fluid communication between the ports  58  and the lower port  52  of the valve  18 , which is also formed in the housing  130 . 
         [0030]    The well fluid that enters the radial ports  58  exerts a pressure on a lower surface of the bellows  150  to form a corresponding upward force on the bellows  150 . This upward force, in turn, is countered by a downward force that is created by a stored gas charge. The bellows  150  is connected to the operator  112  of the yoke  106  so that upward and downward movement of the bellows  150  induces a corresponding longitudinal translation of the yoke  106  and thus, controls the open and closed state of the ball valve  19 . 
         [0031]    A force that is created by gas in a pressurized upper gas chamber  160  of the gas lift valve  18  exerts a downward force on the opposite side of the bellows  150 . In general, the gas pressure inside the chamber  160  biases the yoke  106  downwardly, thereby biasing the ball valve  19  to rotate to a position to form a fluid blocking seal against a valve seat  177  to close the valve  19 . This biasing force, in turn, is overcome when the pressure that is exerted by the annulus fluid exceeds a predefined threshold. When this occurs, the upward force on the bellows  150  exceeds the downward force exerted by the gas in the chamber  160  to cause upward movement of the bellows  150  and yoke  106 , thereby transitioning the ball valve  19  to its open state and permitting fluid communication through the ball valve seat  177  and port  52 . 
         [0032]    The annulus pressure required to open the ball valve  19  is set by the pressure charge inside the chamber  160 . As depicted in  FIG. 5 , as a non-limiting example, the threshold may be established by adjusting the pressure of the gas charge. The gas may be introduced into the chamber  160  at an inlet fill port  170  in the outer housing  130 . 
         [0033]    In general, when the ball valve  19  is open, fluid is communicated between the inlet ports  58  and the outlet port  52  of the gas lift valve. As depicted in  FIG. 5 , as an example, the gas lift valve  18  may include a venturi  182  that is located between the ball seat  177  and the outlet  52 . In general, the venturi housing  182  includes a venturi orifice  186 , which minimizes turbulence in the flow of gas from the well annulus to the central passageway of the production tubing string  15 . 
         [0034]    In accordance with a non-limiting example, the gas lift valve  18  may include energized seal assemblies  200  (T-seal assemblies, V-seal assemblies, chevron assemblies, o-ring assemblies, etc.) to seal the ball element  110  against the ball valve seat  177 . The energized seal assemblies  200  relax the tolerance requirements for the ball valve  19  and permit ease of operating the ball valve  19 , especially in the case of high annulus pressures. 
         [0035]    While the present invention has been described with respect to a limited number of embodiments, those skilled in the art, having the benefit of this disclosure, will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.

Summary:
A gas lift valve assembly includes a housing that includes a first passageway that is substantially concentric with the central passageway of a string to communicate well fluid and a second passageway that is eccentrically disposed with respect to the central passageway to communicate a second fluid to lift the well fluid. The gas lift valve assembly includes a valve that is disposed in the second passageway and includes a ball valve to regulate communication of the second fluid.