Abstract:
A double action locking jar is operable to provide a jarring force in an upward or downward direction. A pair of pressure pistons form a pressure chamber in which a Belleville spring stack is located. A metering orifice in one of the pistons serves to provide a delay mechanism for release of a mandrel within the housing. Two collets are located within the housing for mechanically releasing the mandrel when a tension or compression force is applied to the mandrel. The jar may be mechanically actuated only by allowing the pistons to freely move within the housing without hydraulic resistance.

Description:
BACKGROUND OF INVENTION 
       [0001]    1. Field of Invention 
         [0002]    This invention is directed to a work string jar which is capable of applying an upward or downward jarring force on a work string used in oil or gas wells. 
         [0003]    2. Description of Related Art 
         [0004]    Double acting jars are known in the prior art however they have certain drawbacks. A known double acting jar is disclosed in U.S. Pat. No. 5,624,001. This jar requires two sets of Belleville spring stacks which add to the complexity and length of the jar. The high pressure seals within the tool are exposed to the drilling mud which can cause premature failure due to the corrosive and abrasive nature of the drilling mud. Furthermore each of the pressure pistons requires an orifice and a check valve. Also this prior art jar does not include a trigger sleeve which reduces wear on the collet and release mechanism. 
       SUMMARY OF THE INVENTION 
       [0005]    A sealed double acting jar with a floating piston to balance the interior fluid with hydrostatic pressure, and a hammer and anvil surface is disclosed. The jarring mechanism includes two pressure pistons which oppose each other to form a substantially sealed pressure chamber. A spring is positioned between the pressure pistons such that when one piston is moved toward the other piston, the spring creates a mechanical resistance at the same time as the compression of the fluid between the pistons creates a pressure, both of which resists movement of the piston. By requiring the piston to move a given distance the minimum load at the trigger point of the jar can be controlled by the compression of the Belleville spring stack. The actual load at the trigger point is a result of the tensile or compressive load placed on the jar by the work string and is balanced by the pressure differential across the piston acting on the cross sectional area of the piston. At least one pressure piston has a first flow passage or an orifice device to control the time delay and at least one pressure piston has a second flow passage or a check valve to allow the fluid to return to the pressure chamber. The jar has separate trigger mechanisms for jarring in tension or compression, however each is a mirror of the other. Each consists of a compression sleeve to transfer the jar load from the collet to the pressure piston, a trigger sleeve to allow the collet to release the inner mandrels after the specified travel has occurred and a coil spring to allow the trigger sleeve to move axially with respect to the collet to prevent damage to the load bearing surfaces. When jarring in either direction the non load bearing collet remains attached to and moves with the mandrel. The pressure pistons slide and seal on a flow sleeve. A fluid passageway is provided which allow the portions of the fluid chambers above and below the pressure pistons to communicate so that the fluid surrounding the chamber defined by the pressure pistons is maintained at hydrostatic pressure. 
         [0006]    This configuration has many advantages over the existing art. The spring can be configured to define a minimum jarring load. This prevents the tool from inadvertently jarring on the surface and eliminates the need to use a safety clamp when racking the tool with drill collars. All of the high pressure is confined to the area between the pressure pistons so that all the seals that are exposed to well bore fluid are balanced with hydrostatic pressure. The collets and spring give a well defined neutral position. This configuration only requires one spring. This design has a hydraulic time delay but triggers mechanically. 
         [0007]    According to another embodiment of the invention, the jar may be mechanically triggered only without the hydraulic time delay by allowing for free movement of the pistons within the housing. 
     
    
     
       DETAILED DESCRIPTION OF THE DRAWINGS 
         [0008]      FIGS. 1A to 5A  are cross sectional views of the jar in a neutral position. 
           [0009]      FIGS. 1B to 5B  are cross sectional views of the jar in an upward jarring position. 
           [0010]      FIGS. 1C to 5C  are cross sectional views of the jar in a downward jarring position. 
           [0011]      FIG. 6  is a perspective view of one of the collets. 
           [0012]      FIG. 7  is a view of the interior and exterior surface of the collet at reference line  8 - 8  of  FIG. 6 . 
           [0013]      FIG. 8  is a view of the internal and external surface of a collet at reference line  9 - 9  of  FIG. 6 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    Referring to  FIGS. 1A-5A , an embodiment of the invention includes an outer housing comprising several portions. These include a sealing cap  14 , a proximal portion  16 , a first filling sub  28 , a proximal trigger sleeve housing  37 , spring housing  68 , distal trigger sleeve housing  99 , a second filling sub  120 , a floating balance piston housing  125  and distal portion  127  which includes threads  129  for connection to a distal portion of the work string. 
         [0015]    The various portions of the housing are secured together by any known method. In one embodiment, the portions are secured together by male and female threaded segments for example  7 ,  8  for the sealing cap  14  and proximal portion  16  of the housing. The first filling sub housing portion  28  has externally threaded stubs  27  and  28  that receive internally threaded portions  5  and  6  of proximal portion  16  and trigger sleeve housing portion  37 . Trigger sleeve housing portion  37  is externally threaded at  66  to receive an internally threaded portion  67  of spring housing  68 . The distal portion of spring housing  68  is internally threaded at  98  to receive externally threaded portion  90  of distal trigger sleeve housing  99 . Second filling sub housing  120  has externally threaded stubs  121  and  122  that connect to internally threaded portion  119  of distal trigger sleeve housing  99  and internally threaded portion  124  of floating balance piston housing  125 . The distal portion  126  of floating balance piston housing  125  is internally threaded to receive externally threaded portion  128  of distal housing portion  127 . Suitable seals  3 ,  4 ,  35 ,  36 ,  76 ,  96 ,  97 ,  140 ,  133 , and  144  are provided between the treaded portions. 
         [0016]    Located within the housing for axial movement in both directions from a neutral position is a mandrel  2  which also comprises several sections. A mandrel work string connector portion  12  is threadly connected to a work string connection  11 . A seal  13  is provided between the connecting portions. The distal portion  17  of the work string connection portion is internally threaded to receive an upper mandrel portion  21  which in turn is internally threaded at  62  to receive an externally threaded portion  63  of central mandrel portion  64 . Central mandrel portion  64  is externally threaded at  107  to receive internally threaded portion  103  of distal mandrel portion  113 . Distal mandrel portion  113  is externally threaded at  142  to receive internally threaded portion  141  of lower end mandrel portion  160 . Suitable seals  9 ,  10 ,  106 , and  143  are located at the threaded connections. The mandrel has an internal fluid passageway  150  that extends throughout its length. 
         [0017]    Mandrel connecting portion  12  has an enlarged section  17  that includes a plurality of splines  18  that slide within grooves  19  provided in the inner surface of housing portion  16 . An annular fluid filled chamber  20  is located between mandrel portion  21  and housing portion  16 . A trigger sleeve  39  is positioned within proximal trigger sleeve housing  37  and includes a plurality of grooves  51  on its inner surface. Trigger sleeve  39  includes a shoulder  40  and a reduced diameter portion  41  as shown in  FIG. 2A . A coil spring  38  is captured between stub  28  of first filing sub  25  and the shoulder  40 . A first collet  46  is mounted on upper mandrel portion  21  between the mandrel and the trigger sleeve  39 . The exterior surface of upper mandrel portion includes a plurality of grooves  50  which interact with a plurality of ribs  52  on the interior of the fingers  49  of collet  46  in a manner to be explained below. Collet  46  also includes a plurality of ribs  47  on the outside of the fingers of the collet that interact with grooves  51  located on the interior surface of the proximal trigger sleeve  39  in a manner to also be described. 
         [0018]    A first compression sleeve  54  surrounds the mandrel and is located between the first collet  46  and a first pressure piston  69 . Pressure piston  69  is mounted on a flow sleeve  65  which surrounds central mandrel portion  64  and is provided with a seal  71 . The piston includes a first flow passage or flow control orifice  78  and a second flow passage or a check valve  79 . A plurality of flow channels  70  are formed either in the outer surface of central mandrel portion  64  or on the inner surface of flow sleeve  65  to allow for fluid communication between the chamber or either side of pressure chamber  82 . 
         [0019]    A second pressure piston  93  is mounted on the flow sleeve  65  downhole of the first pressure piston  69  and may include a flow control orifice  80  and a check valve  81  or first and second flow passages. Pressure pistons  69  and  93  are also provided with a flow passage  91  that extend from the metering orifices and check valves to the rear of the pistons as shown in  FIG. 3A . A Belleville spring stack  79  surrounds the flow sleeve and extends between pressure pistons  69  and  91  and is confined between them. Although a Belleville spring stack is illustrated, any known spring such as a coil spring may be utilized. Flow sleeve  65  is captured between portion  62  of upper mandrel portion  21  and portion  103  of lower mandrel portion  113 . Downhole of the second pressure piston is a second compression sleeve  101  and collet  112  arrangement similar to that of compression sleeve  54  and collet  46 . Also a second trigger sleeve  110  surrounds collet  112  and includes a plurality of grooves  116  on its inner surface which interact with a plurality of ribs  111  on the outer surface of the collet fingers. Also distal mandrel portion  113  has a plurality of grooves  152  that interact with a plurality of ribs  114  on the inner surface of the collet fingers. Trigger sleeve  110  includes a shoulder  161  at its distal end and a reduced diameter portion  117 . A coil spring  118  abuts shoulder  161  at one and rests on a shoulder of the sub housing  120  at its other end as shown in  FIG. 4A . Pressure pistons  69  and  93  along with the metering orifice and check valve or first and second flow passages, serve as an hydraulic delay mechanism for triggering the jar. However, it is within the scope of this invention to allow the pistons to move freely within the housing without causing any hydraulic resistance so that the jar is mechanically actuated only. This can easily be accomplished, for example, by allowing sufficient clearance between the pistons and the housing for unrestricted fluid flow. In this situation the pistons would merely function as spring abutment members. 
         [0020]    A floating balance piston  130  having exterior and interior seals  131 ,  132  floats on lower end mandrel portion  160  in a distal pressure chamber  134  formed between the lower portion  160  of the mandrel and housing portion  125 . The distal portion of the pressure chamber  134  is in fluid communication with the fluid passageway  150  in the mandrel, and the proximal portion  135  of pressure chamber  134  is in fluid communication with the interior portion of the tool between the housing and mandrel. 
         [0021]      FIG. 6-8  illustrates the details of collet  46  which is structurally identical to collet  112 . Collet  46  includes a plurality of alternating finger portions  203 ,  204  that are joined at their top looking at  FIG. 6  by arcuate solid portions  200 . At their bottom, the finger portions are joined to a different finger portion by solid arcuate portions  201  thus forming a interconnects series of finger portions with slots  205  open at the top and slots  202  open at the bottom of the collet. The outer surface of each finger portions  203 ,  204  of the collet is provided with a plurality of ribs  47 , the lowermost ribs  49  having a greater width than that of ribs  47 . In a similar fashion the inner surface of each finger portion  203  and  204  are provided with a plurality of ribs  52  and the lowermost rib  206  has a greater width than that of ribs  52 . 
         [0022]    Operation of the jar is as follows. For jarring in the upward mode, an upward force is applied to the mandrel through work string connector  11 . Upward movement of the mandrel is resisted by Belleville spring stack  79  through collet  112 , compression sleeve  101  and pressure piston  93 . Upward movement of the mandrel is also resisted by the fluid within the pressure chamber  82  bounded by the two pressure pistons  69  and  93 . Fluid is allowed to escape from the pressure chamber by the metering orifice  80  provided in one of the pressure pistons. This arrangement acts as a hydraulic time delay to prevent premature triggering of the jar. As the mandrel continues to move upwardly as shown in  FIG. 4B  ribs  111  on the collet  112  will come into registry with grooves  116  provided in the inner surface of trigger sleeve  110 . The proximal ribs on the collet  112  has a width greater than that of the distal ribs and the proximal groove in the trigger sleeve has a width greater than that of the distal grooves to avoid jamming or release of the collet prematurely in a manner known in the art. Once ribs  111  and grooves  116  are in alignment the collet finger expands outwardly and the mandrel is released. This drives hammer portion  152  of enlarged portion  17  of the mandrel against anvil portion  151  of sealing cap  14 , as shown in  FIG. 1B . 
         [0023]    At this point the Belleville spring stack will act to move trigger sleeve  110  to the right looking at  FIG. 4B  through pressure piston  93  and compression sleeve  101 . This in turn compresses coil spring  118 . To reset the jar, the upward force on the mandrel is relaxed. The mandrel returns to a neutral position shown in  FIGS. 1A-5A  and ribs  114  on the inner surface of collet  112  engage grooves  152  on the outer surface of mandrel portion  113 . The width of the grooves  152  and the ribs  114  are formed in the manner of grooves  116  and ribs  111 . Compressed coil spring  118  now moves trigger sleeve to the left looking at  FIG. 4B  to its neutral position in  FIG. 4A . During the upward jarring sequence, collet  46  remains engaged with mandrel portion  21 . 
         [0024]    Downward jarring is achieved by applying a downward force on the mandrel. Collet  46 , compression sleeve  54 , pressure piston  69  and Belleville spring stack all operate in a manner similar to upward jarring. Downward movement of the mandrel with respect to the housing causes collet  46  to release mandrel portion  21  after compressing Belleville spring stack  79  and moving pressure piston  69  to the right as seen in  FIG. 3C . As the ribs  47  on collet  46  register with grooves  51  in trigger sleeve  39 , collet  46  disengages from proximal mandrel portion  21 . This will cause hammer surface  153  of enlarged portion  17  of mandrel portion  12  to strike anvil surface  154  provided on the proximal portion of filling sub housing  25  as shown in  FIG. 26 . This will also compress coil spring  38 . 
         [0025]    To reset the jar, downward force on the mandrel is relaxed and the mandrel will move upwardly with respect to the housing. This will bring grooves  50  on mandrel portion  21  back and into alignment with ribs  52  on the inner surface of the collet  46 . At this point compressed coil spring  38  will move trigger sleeve  39  back to its neutral position. 
         [0026]    An additional aspect of the invention involves providing a flow path  70  between mandrel portion  64  and flow sleeve  65 . This can be accomplished by providing flow channels either on the external surface of the mandrel or on the internal surface of the flow sleeve. These flow channels allow the portions of the fluid chambers distal and proximal to pressure chamber  82  to communicate so that the fluid surrounding chamber  82  is maintained at hydrostatic pressure. 
         [0027]    Although the present invention has been described with respect to specific details, it is not intended that such details should be regarded as limitations on the scope of the invention, except to the extent that they are included in the accompanying claims.