Patent Document

BACKGROUND 
     In the hydrocarbon industry it is common to run a whipstock and a mill in the same run by hanging the whipstock from the end of the mill string. Generally this is done by using a bolt at an uphole end of the whipstock that runs into the mill to support the weight of the whipstock during run in. Once the whipstock has landed at a selected position and orientation within the borehole, the whipstock is anchored in place and will bear weight. The mill is then separated from the whipstock by set down weight on the bolt that extends from the whipstock to the mill. The bolt is sheared to effect separation. Because the whipstock is necessarily thinner at the uphole end thereof, it has commonly been a practice in the industry to use a lug at the uphole end of the whipstock to support the shear load with minimal distortion of the whipstock. While this arrangement does tend to work as planned, it also presents a heavy piece of material that is significantly less than a full circle thereby guaranteeing an interrupted cut. Such interrupted cuts are known to damage the mill but this has traditionally been endured due to the lack of any alternative arrangement that will function more favorably. 
     SUMMARY 
     An affixation and release arrangement includes a first component having a fluid pressure chamber; a piston mounted in the first component and exposed to the fluid pressure chamber; a second component affixed to the first component through the piston, the piston responsive to fluid pressure increase within the chamber to unaffix the second component from the first component. 
     A method for releasing a mill and whipstock combination including pressuring a piston within a chamber of the mill; loading a fastener with the piston; overcoming the fastener; releasing the mill from the whipstock. 
     A method for releasing a mill and whipstock combination including pressuring a piston within a chamber of the mill; loading a securement engaged with the piston; overcoming the securement; releasing the mill from the whipstock. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Referring now to the drawings wherein like elements are numbered alike in the several figures: 
         FIG. 1  is a schematic view of a mill connected to a whipstock with a piston actuated affixation arrangement as taught herein; 
         FIG. 2  is a schematic view of the mill and whipstock disconnected by piston actuation; 
         FIG. 3  is a schematic view of an alternate embodiment. 
         FIG. 4  is a schematic view of an alternate embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1  an affixation and release arrangement  10  is illustrated. The specifically depicted embodiment is an affixation between a first component such as a mill  12  and a second component such as a whipstock  14  but it is to be appreciated that the concept hereof can be extended to other affixations that require separation. Referring directly to the Figures, the mill  12  defines a chamber  16  therein. A piston  18  is disposed in pressure communication with the chamber  16  such that a change in pressure in the chamber will cause a change in position of the piston  18 . In one embodiment, the arrangement is configured to cause the piston  18  to move upon a pressure increase in the chamber  16 . In the illustrated embodiment, this is affected by configuring the piston  18  with a differential area end to end. Hence upon increased pressure, the piston will move. Addressing specifically the differential area of the piston  18 , it is noted that in the illustration, the portion of the piston  18  that for convenience is referred to here as piston head  20 , on the right side of drawing  FIG. 1  is of a dimension that is larger than that of a portion of the piston  18 , referred to herein for convenience as piston tail  22 . Piston head  20  and piston tail  22  are accommodated laterally in the mill  12  in bores  24  and  26  that are sized to promote fluid pressure sealability with the piston head  20  and piston tail  22 , respectively. Sealing is enhanced by the provision of seals  28  and  30  at each of piston head  20  and piston tail  22 . In one embodiment the seals  28  and  30  are o-rings. In the condition of piston  18  as described it will be evident to one of ordinary skill in the art that increasing fluid pressure in chamber  16  will cause the piston  18  to move toward the end thereof that is of greater area. In the configuration described above this is toward piston head  20 . This also corresponds to the right side of the figure as illustrated. 
     In order to prevent the piston from moving too far in either direction the illustrated embodiment is configured with stops  32  and  34 . These are in one embodiment as illustrated with stop  32  being a snap ring received in a groove  36  and stop  32  being a piece of the piston  18  itself. It will be understood however that these can be reversed or the stop function otherwise accomplished. In the specifically illustrated embodiment the construction is related to ease of manufacture of the arrangement  10  since in this configuration the entire piston  18  is insertable through the bore  24  and then the snap ring  32  may be engaged with the groove  36  through chamber  16 . Because in the setting of the illustrated embodiment there is no reason that reengagement would be desired, there is no reason to include a biasing member to urge the piston  18  in a direction opposite that of the direction of movement under increased chamber fluid pressure. It will be appreciated however, that in other embodiments utilizing the same concept as the embodiment illustrated might benefit from a biasing member and hence in such an arrangement a biasing member such as a spring would be located to act in a direction opposite the direction of fluid pressure movement such as in compression between the ring  32  and the chamber wall directly to the right of the ring  32  in the Figure, for example, or might be located to act in a same direction as the direction of fluid pressure movement such as between the stop  34  and the chamber wall directly to the left of the stop  34  in the Figure, for example. 
     The whipstock  14 , for run in, is secured to the mill  12  by a fastener  38  that is in affixed relationship with the piston  18 . In one embodiment, the affixed relationship is a threaded or press fit relationship at interface  40  (illustrated in  FIG. 1  with the thread as top and the press fit as bottom to be illustrative of the two differing embodiments). In some embodiments the threaded engagement, press fit engagement or the fastener itself may be overcome solely by the pressure based movement of the piston resulting in release of the mill  12  from the whipstock  14 . In other embodiments however, it is contemplated that a parting configuration be provided in the fastener. Such parting configurations may present as a groove  43  in the fastener (shown as the bottom only to provide illustration of differing embodiments) to reduce tensile capacity thereof, a heat-treated area for the same purpose, or other similar treatments that will reduce strength of the fastener. In some embodiments the reduction is strength of the fastener will be concentrated in a reduction in tensile strength while substantially preserving shear and/or bending strength. In each case, the parting configuration is configured to cause parting of the fastener  38  below a surface  42  of the whipstock face to ensure that the fastener will not itself present an impediment to mill  12  advancement. 
     With the fastener  38  secured to the piston  18 , through an uphole end of whipstock  14 , the whipstock  14  is affixed to the mill  12  and remains that way until the arrangement is actuated by increasing fluid pressure in chamber  16 . Fluid pressure can be increased in a number of ways such as by pump or by heaters or by energetic compounds (particularly if the chamber  16  is configured as an enclosed space), etc. and the pressure can be locally generated or remote as desired. 
     In use, the arrangement is run into the hole in the condition illustrated in  FIG. 1  and located by suitable means. Once the whipstock is at final destination and orientation the pressure is increased in chamber  16  whereby the piston  18  is moved to the right of the drawing Figure and the fastener  38  parts, which is illustrated in  FIG. 2 . Once the arrangement  10  has achieved the condition illustrated in  FIG. 2 , the mill  12  is free to move relative to the whipstock  14 . Because there is no remaining bolt or lug to be milled off the whipstock  14 , there is far less eccentric cut experienced by the mill when advancing to its primary objective. The life of the mill is therefore extended and the job it can do enhanced since it has not experienced a difficult eccentric cut, as has traditionally been the case. 
     In an alternate embodiment, referring to  FIG. 3 , the piston  118  is configured differently. The piston  118  itself extends through the whipstock  14  and is secured at an opposite surface  44  to the face surface  42 . In the specifically illustrated embodiment, a securement  48  is secured in a groove  50  of the piston  118 . This ring  48  may be a snap ring, an e clip, etc. Further the securement  48  may be a roll pin or other similar structure (schematically represented by  FIG. 4 ). In this embodiment, upon the application of fluid pressure within chamber  16 , piston  118  is urged as it was in the previously described embodiment but instead of parting the fastener as shown in  FIG. 2 , the securement  48  is disengaged from the piston  118 . Disengagement may be by shear, deformation, etc. as long as it is no longer in a position to hold the piston in place and thereby allows the fluid pressure to move the piston  118  in a direction that will disengage the piston itself from the whipstock (to the right in the figure). In this embodiment, there is no component of the securement left in the whipstock and hence no concern that such component might come loose and interfere with a well operation. 
     While preferred embodiments have been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustration and not limitation.

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