Abstract:
A whipstock includes a whipstock body having a diverter face; and a swellable material disposed about the whipstock body and configured, positioned and dimensioned to interact with an inside dimension of a borehole in which the whipstock is run and method.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims priority to U.S. Provisional Patent Application Ser. No. 60/941,810, filed Jun. 4, 2007, the entire contents of which are specifically incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    In connection with the drilling of multilateral wellbores, whipstocks are often placed in a bore from which a lateral borehole is to be drilled. One of the problems associated with the use of whipstocks is that debris tends to collect around the circumference of the whipstock, in an annulus between the whipstock and the casing thereby rendering it difficult to retrieve the whipstock. Metal cuttings during the milling operation tend to collect in this annulus. The cuttings tend to become compacted in the annulus as well then upon an attempt to retrieve the whipstock uphole the cuttings can jam the same rendering it difficult or impossible to remove the whipstock. Moreover, it is not uncommon for formation cuttings or settling of solids in the mud fluid to settle around the circumference of the whipstock as well. Since, in many applications and particularly in Multilateral Wells, the whipstock is intended to be removed from the borehole after use, the collection of debris in the annulus and consequent difficulty or impossibility of removing the whipstock is undesirable. The art, therefore, will receive an arrangement capable of preventing or substantially alleviating the aforenoted problem. 
       SUMMARY 
       [0003]    A whipstock includes a whipstock body having a diverter face; and a swellable material disposed about the whipstock body and configured, positioned and dimensioned to interact with an inside dimension of a borehole in which the whipstock is run. 
         [0004]    A method for preserving whipstock mobility includes applying a swellable material to a whipstock body; running the whipstock in a wellbore; and exposing the swellable material to a swelling fluid. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    Referring now to the drawings wherein like elements are numbered alike in the several Figures: 
           [0006]      FIG. 1  is a schematic elevation view of a first embodiment of an arrangement disclosed herein; 
           [0007]      FIG. 2  is a schematic elevation view of a second embodiment of an arrangement disclosed herein; 
           [0008]      FIG. 3  is a schematic elevation view of a third embodiment of an arrangement disclosed herein; and 
           [0009]      FIG. 4  is a schematic elevation view of a fourth embodiment of an arrangement disclosed herein. 
       
    
    
     DETAILED DESCRIPTION 
       [0010]    Referring to  FIG. 1 , a borehole  10  is illustrated with a window  12  having already been milled by a milling tool (not shown) that will have been deflected from whipstock  14  by a diverter face  16 . The whipstock  14  is anchored in the borehole  10  at an anchor  18 . One of ordinary skill in the art will be familiar with these components. Significantly, an annulus  20  is pointed out that exists between an outside diameter of the whipstock  14  and an inside diameter of the wellbore  10 . This annulus is the one susceptible to collection of debris and consequent application of a retaining force on the whipstock  14  as discussed above. It is desirable, therefore, to prevent the migration of debris into annulus  20 . 
         [0011]    Applicant has discovered a way to effectively prevent the accumulation of debris in annulus  20  by adding a swellable material seal  22  in the form of a toroid around the largest circumference of the whipstock  14  and at a position on whipstock  14  immediately downhole of the whipstock diverter face  16 . This position on the whipstock  14  guarantees that the seal  22  will be immediately adjacent to downhole edge  24  of window  12 . This is advantageous, since in this position any debris dropping on the uphole end of the seal  22  will either fall into the lateral whereafter it will be circulated back to surface, or if it does not fall into the lateral, will be entrained with circulation fluid back to the surface in any event. This will prevent the buildup of debris and the consequent whipstock retrieval difficulties noted above. 
         [0012]    The seal  22  comprises a swellable material because such material allows the seal  20  to itself have a smaller outside dimension during running and then to attain a larger outside dimension sufficient to seal against the wellbore  10  when the swellable material is exposed to a swelling fluid. The smaller initial outside dimension reduces damage to the seal during running up the whipstock to depth and further renders the running operation easier because it leaves a greater amount of open space between the whipstock end seal and the inside dimension of the wellbore  10 . The swellable material may be of any type such the ultimate sealing is ensured. In one embodiment, the material is responsive to one or more of water, oil and methane and the reaction begins immediately upon the whipstock being introduced to the borehole. In other embodiment, the material is responsive to one or more of water, oil and methane at the reaction does not occur until later in the run of the whipstock. It may be that the swelling fluid is actually injected into the well or it may be that the fluid is an environmentally present fluid in the wellbore. 
         [0013]    Referring to  FIG. 2 , it will be appreciated that the figure is nearly identical to that of  FIG. 1  with the difference being the configuration of the seal identified in  FIG. 2  by numeral  122 . In this embodiment, the seal remains a swellable material but is significantly wider than the first embodiment disclosed to have the appearance of a band. The second embodiment works similarly to the first with respect to swelling but may be more tolerant to geometric aberrations at the inside dimension of the wellbore  10  due to its width. 
         [0014]    Referring now to  FIG. 3 , another alternate embodiment of the arrangement is disclosed. In this embodiment it will be noted that an area  230  located behind diverter face  16  creates a partial annulus between the whipstock  14  and the wellbore  10 . While it is believed that most of the debris that might fall within this space will exit the space on its own due to circulation, it is still possible that some of the debris may build up and create difficulties with respect to retrieval of the whipstock. In order to alleviate the situation, the embodiment of  FIG. 3  effectively coats nearly the entirety of the surface of the whipstock with seal material  222  as illustrated in  FIG. 3 . It will be appreciated that in this embodiment when the swellable material expands all but the bottommost portion of the whipstock  14  and the diverter face  16  is sealed against portions of the inside dimension of the wellbore  10 . In such configuration, it is certainly nearly impossible for any debris to collect around the whipstock  14 . In other respects, this embodiment functions as does those set forth hereinabove. 
         [0015]    Referring to  FIG. 4 , yet another embodiment in accordance with the disclosure hereof is illustrated. This embodiment reduces the required amount of swellable material while still producing a fully sealed configuration of the whipstock. In this embodiment, it will be appreciated that the seal  322  is oriented such that it parametrically surrounds the diverter face  16 . This ensures that there is no space between the whipstock  14  and the inside dimension of the wellbore  10  at all and yet the configuration does not require the quantity of swellable material required in the embodiment of  FIG. 3 . Further, because there is less swellable material, there is a smaller moment created on the whipstock  14  that otherwise requires consideration relative to the uphole end  240  of the whipstock moving toward a more central location of the wellbore  10 . This consideration is needed to ensure that the system will not allow the milling tool (not shown) to impact end  240  and/or will not adversely affect the desired angle of departure of the milling tool. 
         [0016]    While preferred embodiments have been shown and described, 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 illustrations and not limitation.