Abstract:
A safety apparatus for catching a test fixture released from a shaft of a downhole tool during the uphole calibration and testing of the shaft force generation capability of the tool. The safety apparatus includes a hollow body having a distal end that will partially envelope the test fixture to catch the test fixture once the test fixture is released from the downhole tool. The safety apparatus further includes a proximal end portion that is releasably securable to the body of the tool. A method for testing and calibrating the tool is also provided.

Description:
BACKGROUND OF THE INVENTION 
     Test fixtures are used in association with downhole tools during the uphole testing of the downhole tools. One such downhole tool is a downhole power unit. A downhole power unit is an electro-mechanical device that is designed to produce a linear force for setting (or pulling) wellbore tools such as monolocks, bridge plugs, packers and the like. A shaft extending axially from the end of the downhole is utilized to transmit this force. The downhole tool is tested uphole prior to insertion downhole to calibrate the tool and ensure that the tool can exert the appropriate amount of force via the shaft as required for a particular application, such as, for example, setting a packer having a 60,000 lb f  activation threshold. 
     During these tests, using shear pins, the test fixture is attached to the end of the rod extending from the downhole tool. An axial force is applied to the test fixture via the rod until the shear pins fail. As a result of the high testing forces imposed on the test fixture by the rod, the test fixture is forcibly expelled from the downhole tool at a high velocity. Likewise, portions of the shear pins are separated from the test fixture during the process. Both the separated text fixture and the shear pins can present danger to personnel in the area of the tests. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the present disclosure and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying figures, wherein: 
         FIG. 1  schematically depicts a downhole power unit and test apparatus for use in the uphole testing of the power unit, the test apparatus including a test fixture and a specially designed safety structure operative to partially surround and catch the test fixture, and associated shear pin portions thereof, when the fixture is released from the power unit during the test; 
         FIG. 2  is a top side perspective view of the safety structure with a pivotally mounted side wall portion thereof in a closed position; 
         FIG. 3  is a perspective view of the side wall portion removed from the safety structure; 
         FIG. 4  is a perspective view of the safety structure with the side wall portion removed therefrom; 
         FIG. 5  is a side elevational view of the power unit operatively coupled to the test fixture in preparation for the uphole test of the power unit using the safety fixture, a portion of which is schematically shown in phantom in  FIG. 5 ; 
         FIG. 6  is a top side perspective view of the power unit/test fixture assembly of  FIG. 5  with the safety structure operatively mounted on the power unit and partially surrounding the test fixture; 
         FIG. 7  is an enlarged scale simplified cross-sectional view, partially in elevation and partially in phantom, taken through the  FIG. 6  apparatus generally along line  7 - 7  and illustrating the operation of the test apparatus; and 
         FIG. 8  is a simplified cross-sectional view through an alternative embodiment of the test fixture and illustrates its use in testing the power unit and providing for calibration thereof. 
     
    
    
     DETAILED DESCRIPTION 
     In the detailed description of the invention, like numerals are employed to designate like parts throughout. Various items of equipment, such as pipes, valves, pumps, fasteners, fittings, etc., may be omitted to simplify the description. However, those skilled in the art will realize that such conventional equipment can be employed as desired. 
     In general, a downhole tool is operable to selectively generate a linear force that may be used to set wellbore devices such as packers and plugs. The downhole tool is tested uphole prior to insertion downhole to calibrate the tool and ensure that the tool can exert the desired amount of force for a particular application, such as, for example, setting a packer having a 60,000 lb f  activation threshold. As will be described in greater detail below, one or more shear pins are used in the testing process and incorporated in a test fixture to simulate the activation threshold for a particular application. In this example, a plurality of shear pins are used to simulate the 60,000 lb f  activation threshold. The shear pins are selected to shear under application of an axial force once the threshold is reached. For example, twelve shear pins may be used with each shear pin rated at 5,000 lb f  so that the total force required to shear is 60,000 lb f . Upon shearing of the pins, the sheared pins and test fixture are forcibly expelled from the tool at a fairly high velocity. The safety structure of the present invention is positionable on the downhole tool so as to partially surround the test fixture in order to catch and retain the test fixture and the pieces of the shear pins expelled from the tool, thereby enhancing the safety of personnel working near the test site. 
     Referring to  FIG. 1 , schematically depicted in an exemplary embodiment, is a downhole tool  10  to selectively generate a linear force on a testing apparatus  11 . In the exemplary embodiment, the downhole tool  10  is a downhole power unit, however, the downhole tool could be other types of tools consistent with the uses of the safety structure. The testing apparatus  11  includes a test fixture  12  and a safety structure  14 . The power unit  10 , as is known to one of ordinary skill in the art, is operable to axially extend or retract a rod  16  out of an end  17  of the power unit  10  in order to, for example, operate wellbore devices such as plugs and packers (not shown). The power unit  10  may include electrical power leads  18  and/or data transmission leads  20 . During uphole testing, the power unit  10  is preferably supported in horizontal position by suitable stands (not shown), as is known to one of ordinary skill in the art. A collar  22  may be mounted around the end  17  of the power unit  10  in order to aid in the testing of the power unit. 
     The outer body of test fixture  12  is of a tubular configuration and includes one or more, and preferably a plurality, of radial holes or apertures  24 . In one preferred embodiment, sets of radial holes  24  are aligned with one another and positioned to form a ring about the circumference of the test fixture body. The test fixture  12  is configured to retain a piston member (not shown in  FIG. 1 , but explained in greater detail below) within its interior using shear pins  26  passing through apertures  24 . As will be explained in greater detail below, the piston member also is threadingly connected to the rod  16  of the downhole tool  10 . 
     At the distal end, the safety structure  14  includes a cylindrical, hollow test fixture retaining section  30  that is disposed to partially surround the test fixture  12  when the safety structure  14  is mounted on the power unit  10 . At the proximal end, the safety structure  14  includes a cylindrical tool mounting section  31 . Preferably, the distal end of safety structure  14  is closed while the proximal end of safety structure  14  is open. The safety structure  14  attaches to the power unit  10  through the use of the cylindrical tool mounting section  31  which includes a pivotal side wall portion  32 . The side wall portion  32  is secured by hinges  34  and pivots open so that the cylindrical tool mounting section  31  can be disposed around an end portion of the power unit  10 . The side wall portion  32  is then closed over the power unit  10  to securely fasten the safety structure  14  to the power unit  10 . 
     The tool mounting section  31  is shown in  FIGS. 1 and 2  with the side wall portion  32  in a closed position. The side wall portion  32  may be secured in a closed position with any suitable fastener, such as for example, the illustrated bolt  38  and nut  40 . The tool mounting section  31 , i.e., the proximal end of safety structure  14 , has a smaller diameter than the cylindrical test fixture retaining section  30 , i.e., the distal end of safety structure  14 . A frustoconical section  36  connects and supports the tool mounting section  31  to the cylindrical test fixture retaining section  30 . An optional top side opening  42  may be provided and extends along the sections  30 , 31  and  36  as shown. The opening  42  covers approximately 180 degrees of the circumference of the tapered diameter section  36  and the test fixture retaining section  30  and occupies the entire axial length of the tapered diameter section  36  and approximately one-third of the axial length of the test fixture retaining section  30 . 
     The opening  42  aids in the mounting and removal of the safety structure  14  to and from the assembly of the power unit  10  and the test fixture  12 . The opening  42  also permits access to and in some embodiments retrieval of the test fixture  12  and shear pins without removing the safety structure  14  from the power unit  10 . 
     Referring to  FIG. 3 , the side wall portion  32  includes a half-cylindrical body  44  with a latching mechanism  46 , such as a plate, mounted on the exterior of one side near the edge of the axial length wise dimension of the half-cylindrical body  44 . In one preferred embodiment, the latching mechanism  46  has a U-shaped opening  48  formed in a plate which opening is configured to receive bolt  38 . Mounted on the other edge of the axial length wise dimension of the half-cylindrical body  44  are hinge components, such as plates  50  and  51 . Plates  50  and  51  each contain an aperture  52  so as for form hinge  34 . Those skilled in the art will appreciate that while side wall portion  32  is preferable for securing safety structure  14  to downhole tool  10 , other structures and mechanisms are also suitable for this purposes, such as for example, bands that wrap around the circumference of tool  10 . 
     Referring to  FIG. 4 , the safety structure  14  is shown with the side wall portion  32  removed. The safety structure  14  may include complimentary hinge elements. In the preferred embodiment, such hinge elements are two pairs of plate sets mounted on the exterior of an edge of the axial length wise dimension of the tool mounting section  31  to form devises  53  and  55 . The devises  53  and  55  will receive the two plates  50  and  51  mounted on the side wall portion  32  so that the apertures  52  and the apertures of the devises (not shown) are aligned. A pin (not shown) may then be inserted into the aligned apertures to form the hinges  34 . 
     The safety structure  14  also includes a third pair of plates  57  mounted on the exterior of the other edge of the axial length wise dimension of the tool mounting section  31 . The bolt  38  is rotatable mounted within this third pair of plates  57 . A circular plate  54  is connected to the rear end of the test fixture retaining section  30  to close the far end  56  of the safety structure  14 . 
     Referring to  FIGS. 5-7 , in an exemplary embodiment, test fixture  12  is shown attached to power unit  10 . Likewise, safety structure  14  (shown in phantom in  FIG. 5 ) is attached to the power unit  10  and positioned to partially surround test fixture  12 .  FIG. 6  illustrates a top side perspective view of the safety structure  14  operatively mounted on the power unit  10  and partially surrounding the text fixture  12 . Power unit rod  16  has an outer end  58  that is threadingly connected to a piston  60  releasably held within the tubular body of the test fixture  12  by the shear pins  26 . The interior of the test fixture body has diameter that is larger than the outside diameter of the piston  60 , thereby permitting axial movement of piston  60  when not secured in place by shear pins  26 . As mentioned above, the tubular body of the test fixture  12  preferably includes a plurality of aligned radial apertures  24  located in a ring about the circumference of the test fixture. As illustrated in  FIGS. 5 and 8 , there may be two such rings in some embodiments, each set of apertures corresponding to a separate piston secured within test fixture  12 . In any event, piston  60  includes a plurality of corresponding apertures  61  for receipt of shear pins  26  when apertures  61  and  24  are aligned. Piston  60  may also include a cavity  62  configured to receive the ends of shear pins  26  that are pressed through the aligned radial apertures  24  and  61 . After the shear pins  26  are pressed through the radial apertures  24  of the test fixture  12  and into the corresponding apertures  61  of the piston  60 , the piston is secured to the test fixture  12 . The rod  16  of the power unit  10  is shown retracted into the power unit  10  so that one end of test fixture  12  abuts the collar  22  of the power unit  10 , preferably without interfering with the extended threaded end of tool  10 . 
     The safety structure  14  is mounted to the power unit  10  so that the safety structure  14  partially surrounds test fixture  12 , as shown in  FIG. 6 , by opening the pivotally mounted side wall portion  32  and placing the tool mounting section  31  around a portion of the cylindrical body of the power unit  10 . The pivotally mounted side wall portion  32  may then be closed over the power unit  10  and secured in place by engaging bolt  38  with the U-shaped opening  48  of the plate  46  and tightening the nut  40  onto the bolt. The safety structure  14  is positioned on the power unit  10  so that the opening  42  is facing substantially upward relative to the horizontal. 
     Still referring to  FIG. 7 , during testing of the power unit  10 , the power unit  10  exerts a force to retract the rod  16  within the power unit, in the direction of arrow  64 . The test fixture  12 , because it is ultimately attached to the rod  16  through the engagement of the rod by the piston  60  and the piston is secured to test fixture  12  via shear pins  26 , will then move in the direction of arrow  64  until the end of the test fixture abuts collar  22  of the power unit  10 . After the test fixture  12  abuts collar  22  of the power unit  10 , continued retraction of rod  16  by the power unit  10  results in an increasing amount of force exerted by the power unit  10  on the piston and shear pins  26  until the axial force exceeds the shear force breaking point of the shear pins  26 , thereby causing the shear pins  26  to shear and the piston  60  to be released from its fixed position within test fixture  12 . Typically, the amount of force required to shear the shear pins  26  often causes the test fixture  12  to be forcibly expelled, after the shear pins  26  break, in a direction away from the power unit  10 , as indicated by directional arrow  66 . After pins  26  shear, the piston  60  and rod  16  may continue to move axially in the direction of arrow  64  towards the power unit  10 . The movement of the piston  60  in the direction of arrow  64  and the movement of the test fixture  12  in the direction of arrow  66  results in release of the test fixture  12  from engagement with piston  60  and rod  16 , such that test fixture  12  will be ejected from the end of power unit  10  and settling within the test fixture retaining section  30  of the safety structure  14 . In addition to safely “catching” the expelled test fixture  12 , the safety structure  14  also serves to “capture” the pieces of the shear pins  26  after the shear pins break. 
     Referring to  FIG. 8 , in another embodiment, a test fixture  70  includes two circumferential rows of aligned radial apertures  24 . The two rows of aligned radial apertures  24  allow the use of the piston  60  and a second piston  72  which are both connected to the test fixture  70  through the use of shear pins  26 . The second piston  72  has a bore  74  with an internal diameter that is larger than the external diameter of the rod  16 , allowing the rod  16  to pass through the second piston  72 . The rod  16  is connected in a suitable manner to piston  60 , and as described above, may be threadably connected to the piston  60 . 
     Testing of the power unit  10  with the test fixture  70  is similar to the procedure described above. After the rod  16  is retracted within the power unit  10  so that the test fixture  70  abuts the power unit  10 , the power unit  10  increases the force on the rod  16  until the shear pins  26  attaching the piston  60  to the test fixture  12  shear and allow piston  60  to move in the direction of arrow  64 . The power unit  10  continues to retract rod  16  in the direction of arrow  64  until the piston  60  abuts the second piston  72 . The power unit  10  then again increases the force on the rod  16  until the shear pins  26  attaching the second piston  72  to the test fixture  12  shear and allow the piston  60 , the second piston  72 , and rod  16  to move in the direction of arrow  64 . 
     The use of text fixture  70  along with second piston  72  allows an operator of the power unit  10  to make an initial test and measure, for example, how much electrical current is required in order to shear the shear pins  26  connecting the piston  60  to the test fixture  12 . The measured electrical current value then corresponds to a known force value because the force value is known from number of shear pins and the force rating for each shear pin. For example, if twelve shear pins are used and each pin is rated for 5,000 lb f , then the current value measured at the time the shear pins break corresponds to 60,000 lb f . A force regulating device of the power unit  10  can be calibrated to use the measured current value for the known force value. The second piston  72  is attached with an identical number of identical shear pins and a second test is performed with the second piston  72  that allows the operator to verify that the current measured with piston  60  will shear the equivalent rated shear pins on piston  72  and that the power unit  10  is properly calibrated. 
     While certain features and embodiments of the invention have been described in detail herein, it will be readily understood that the invention encompasses all modifications and enhancements within the scope and spirit of the following claims. Furthermore, no limitations are intended in the details of construction or design herein shown, other than as described in the claims below. Moreover, those skilled in the art will appreciate that description of various components as being oriented vertically or horizontally are not intended as limitations, but are provided for the convenience of describing the invention. 
     For example, the test fixture is described as cylindrical in shape, although other shapes of the test fixture may be used. In addition, it is not necessary that a piston inside of a cylindrical test fixture be utilized, rather, the rod may be directly connected to the test fixture via shear pins. It is also not necessary that shear pins be utilized to secure the rod (either directly or indirectly) to the test fixture. Devices other than shear pins are contemplated to provide a targeted separation force between rod and the test fixture. For example, test fixture  12  may be provided with an enclosed distal end and one or more bolts having known axial tensile rupture limits may secure the rod to the test fixture. Upon application of an axial force by the rod, the bolts will axially rupture at a known tensile value. Thus, the invention is not limited to a particular type of rupture separation between the test fixture and the power unit. 
     Likewise, the safety structure need not be of cylindrical construction. The opening  42  need not be provided, rather, a fully enclosed structure could be provided that uses a panel that can be opened to retrieve the test fixture and shear pins following a test. The tool mounting section of the safety structure also does not need to have a pivotally mounted side wall portion in order to attach to the downhole tool, other forms of attaching to the downhole tool are contemplated. 
     It is therefore evident that the particular illustrative embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the present invention. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee.