Abstract:
The present invention provides an apparatus for launching spheres into a gas riser in order to reduce the risk that the output from the riser is lost. The apparatus comprises a rotatable body that is rotated to a first position to receive an object from an object storage means in an aperture and the rotatable body is then rotated to a second position such that the object received in the aperture is received within a riser.

Description:
BACKGROUND 
     a. Field of the Invention 
     The invention relates to an apparatus for launching a series of spheres and in particular to an apparatus for launching a series of spheres into a gas producing well. 
     b. Related Art 
     It is a widely accepted understanding that with aged wells, or in some circumstances due to well bore formation on gas wells, production may be problematic or cease totally. Typically, this is due to the well bore formation which has a high ingress of fluids, for example water, which chokes the well bore. The volume of the well bore produced fluids can create a greater hydrostatic pressure acting on the well bore and be greater than the pressure of the produced gas. This can lead to loss or failure of the producing section of the well bore. 
     It is also known to that to solve the problem, it is necessary to reduce the effects of the well bore produced fluids by isolating the fluid producing section of the reservoir or lifting the fluid to allow production. One method to isolate the water producing section of the reservoir is through the introduction of spheres which are heavier than the well bore fluids, which act to reduce the well bore cross-sectional area and limit the rate of water ingress into the well bore. The spheres will produce a honeycomb effect within the well bore and help to maintain a higher gas pressure, thus allowing gas production through the honeycomb of spheres. Some systems for introducing these spheres are commercially available but these have a number of disadvantages, the most important of which are that the size of sphere that can be used is limited and the loading of the spheres into the systems can take a considerable period of time. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the present invention there is provided an apparatus for providing a supply of objects to a riser, the apparatus comprising a rotatable body, such that, in use the rotatable body is rotated to a first position to receive an object from an object storage means in an aperture and the rotatable body is then rotated to a second position such that the object received in the aperture is received within a riser. 
     The invention allows a consistent supply to be provided to the riser, with the rate at which the spheres are supplied being determined by the number of apertures in the rotatable body and the speed that the body is rotated at. 
     Preferably, the first position is vertically aligned with the second position. The rotatable body may comprise two apertures. 
     The apparatus preferably further comprises an object storage means configured to supply objects to the rotatable body. The object storage may comprise means for pressure sealing the storage means and preferably further comprises means for pressurising the apparatus to substantially the same pressure as the riser. 
     The storage means is preferably a wireline lubricator that can store enough objects for continuous operation in excess of two hours. Such a storage means can be changed relatively quickly and easily, with a minimal impact on operational timings. 
     The rotatable body is received within a housing and may be rotatably mounted on an axle, the rotatable body further comprising one or more sealing means received around the axle. The drive means may be received outside the housing and mounted on the housing. The object storage means may be received outside the housing and the apparatus may further comprise a first connector for connecting the housing to the object storage means, the first connector being located vertically above the first position. The apparatus may also comprise a second connector for connecting the apparatus to a riser, the second connector being located vertically below the second position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1 ,  1   a  and  1   b  show a schematic depiction of an apparatus according to the present invention; 
         FIG. 2   a  shows a schematic depiction of a perspective view of the sphere launcher according to one embodiment of the invention; 
         FIG. 2   b  shows a schematic depiction of a radial cross-section of the sphere launcher according to one embodiment of the invention; 
         FIG. 2   c  shows a schematic depiction of an axial cross-section of the sphere launcher according to one embodiment of the invention; and 
         FIG. 3  shows a further schematic depiction of an axial cross-section of the sphere launcher. 
     
    
    
     DETAILED DESCRIPTION 
     The invention will now be described, by way of example only, with reference to the Figures in which  FIGS. 1 ,  1   a  &amp;  1   b  show a schematic depiction of an apparatus  10  according to the present invention, the apparatus being coupled to a Christmas tree  20  that is coupled to the upper end of a riser (not shown) in a conventional manner. The apparatus  10  comprises a sphere launcher  30 , which is coupled to the riser via a Christmas tree  20 . 
     The apparatus comprises a loading hopper  2  that is separated from the first end of a sphere loading means  6  via first pressure isolation means  4 . The second end of the sphere loading means  6  is connected to the first end of a sphere storage means  12  via second pressure isolation means  8 . Spheres  18  that are held within the sphere storage means  12  can then pass into the sphere launcher  30 .  FIG. 1  shows that one of the spheres is held within the sphere dropper  70 . The sphere dropper is rotatable (see below) such that only a single sphere is held within the sphere dropper (see  FIG. 1   a ). As the sphere dropper is rotated further (see  FIG. 1   b ), the sphere is dropped into the riser via the Christmas tree  20 . 
     During the operation of the apparatus the sphere loading means and the sphere storage means are pressurised to the well pressure. This may be achieved by providing a pressure equalisation line  14  from the Christmas tree to the sphere loading means and appropriate control means  16  to regulate the pressure applied to the sphere loading means. The first pressure isolation means  4  enable spheres loaded from the sphere hopper to enter into the sphere loading means without losing pressure in the sphere loading means. Similarly, the second pressure isolation means enables the sphere loading means to be exposed to the external pressure whilst still maintaining the required pressure within the sphere storage means or the sphere dropper. 
       FIGS. 2   a ,  2   b  and  2   c  show schematic depictions of a sphere launcher  30  according to one embodiment of the invention.  FIG. 2   a  shows a perspective view of the sphere launcher,  FIG. 2   b  shows a radial cross-section of the sphere launcher and  FIG. 2   c  shows an axial cross-section of the sphere launcher. The sphere launcher  30  comprises an axle  50 , bearing  60 , bearing cap  62 , locking means  64  &amp;  66 , sealant injection means  67 , seal means  68 , washers  69 , and sphere dropper  70 . The sphere dropper  70  comprises first and second apertures  72 ,  74  and adjustment means  76 . 
     The sphere dropper  70  is received on the bearing  60 , which is coupled to the axle  50  such that when the axle is rotated, the bearing causes the sphere dropper to rotate. The sphere dropper  70 , in use, is configured such that when the first aperture  72  is aligned with the aperture of the Christmas tree, the second aperture  74  is aligned with the sphere storage means  12 . The second aperture will then receive a sphere from the sphere storage means  12  and a sphere received within the first aperture will move from the sphere dropper into the Christmas tree and then into the riser. The axle is coupled to a motor (not shown) that causes the sphere dropper to rotate. When the sphere dropper is rotated through 180° then the sphere received in the second aperture  74  will move into the riser, via the Christmas tree. Also, the first aperture is now aligned with the sphere storage means  12  and thus a further sphere will be received within the first aperture. The continued rotation of the sphere dropper  70  will cause the sphere launcher to provided a regular supply of spheres into the riser. 
     In order to avoid the well pressure from forcing the spheres back out of the riser, the sphere launcher and the sphere storage means are pressurised and comprise a pressure equalisation system to ensure that the apparatus provides a pressure that is equal to that of the well to avoid differential pressure acting on the spheres. Accordingly, the sphere launcher shown in  FIG. 2  is received within a housing which is adapted to be securely connected to the bearing cap  62 . Seal means  68  preferably comprise two sets of chevron seal stacks to seal the interior of the sphere launcher. The sphere launcher may also comprise sealant injection means  67 , which is preferably a cross drilled injection port enabling the injection of plastic grease lubrication packing should a further method of sealing be required. The injection port may be provided between the two sets of chevron seal stacks or on the interior or exterior side of the chevron seal stacks. 
     In order to reduce the wear on the stem, chevron seal stacks and the bearing it is preferred to rotate the sphere dropper at a relatively low speed. In a preferred example, the sphere dropper is rotated once every 12 seconds, such that one sphere is dropped every 6 seconds. This also enables the spheres to be dropped into and from the sphere dropper without the sphere becoming fouled in the rotation of the sphere dropper. 
       FIG. 3  shows the sphere launcher described above with reference to  FIG. 2  when received in a housing  80 . The bearing cap  62  is secured to the housing conventional techniques and the axle stub  75  is supported within the housing such that it can be rotated. The free end of the axle  50  is received within a coupling  90  that is connected to a rotary drive means  95 . Preferably the rotary drive means comprises a planetary gear box, geared to suit the rotational speed that the sphere launcher is rotated at, driven by a hydraulic motor that is fed from a pneumatically driven hydraulic pump unit. The rotation of the sphere launcher and the number of sphere drops can be recorded using a simple trip counter. A flange  85  to the housing  80  may be provided to support the coupling and the rotary drive means. Additional support means  88  may be provided to reinforce and stiffen the flange. The housing is preferably provided with conventional box  100  and pin  110  connections to allow the sphere launcher to be connected to the sphere storage means and the Christmas tree respectively. Preferably the axle stub is supported using a self lubricating thrust bearing arrangement and the other end of the sphere dropper is preferably supported in a similar manner to enable the free rotation of the sphere dropper with the weight of the sphere storage means from above. 
     It will be understood that in use the sphere launcher will be configured such that the box connection  110  is vertically upwards and the pin connection  100  is vertically downwards. The sphere dropper is received within the housing such that the apertures  72 ,  74  are aligned with the box and pin connections such that a sphere received from the sphere storage means will pass through into the Christmas tree. 
     The sphere storage means  12  preferably comprises a conventional wireline lubricator. For a 2 inch (50 mm) sphere, it has been found that it is possible to store 140 spheres per metre length of lubricator, enabling 1400 spheres to be stored in a conventional lubricator. At a dispensing rate of 1 sphere per 6 seconds this provides 140 minutes of operation per lubricator. The lubricator is pressurised to well pressure during operation and may be vented during refilling operations. The first and second pressure isolation means preferably comprise a double isolation valve. The internal diameter of the sphere storage means and the first and second pressure isolation means are preferably 63 mm (2.5 inches) 
     The spheres preferably have a 2 inch (50 mm) diameter and are made of a solid material that will not react with any of the materials found in the offshore environment and is suitably robust to avoid mechanical damage. It has been found that polypropylene is suitable for use. It will be understood that this does no preclude the use of other material for the spheres. The size of the spheres may also be altered dependent on the bore of the riser and the size of the apertures in the sphere dropper. It has been found that a 2 inch (50 mm) diameter sphere avoids fouling the dropper and provides a sufficient obstruction within the riser to provide the required increase in pressure. The rate at which the spheres are dropped into the riser may be varied as long as the risk of a sphere fouling in the sphere dropper is maintained at a suitable level. The sphere dropper may comprise one, two or more than two, aperture(s).