Abstract:
A technique for manufacturing a millable bridge plug for plugging of a wellbore during, for example, a fracturing operation. A bridge plug is constructed with an obstructed internal passage. The obstructed internal passage is formed by winding a composite material about a wrapping mandrel having at least one cylindrical part and a solid part coupled thereto. The cylindrical part is removed after a curing process leaving a mandrel with a plugged internal passageway upon which a seal member combined with a plurality of slips for engaging a surrounding wall, e.g. a surrounding wellbore wall, may be coupled.

Description:
CROSS-REFERENCE 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 62/316,566, filed on Apr. 1, 2016, the disclosure of which is hereby incorporated by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure relates to plug systems having nonmetallic components to facilitate milling. 
       BACKGROUND 
       [0003]    Many millable frac and bridge plugs utilize nonmetallic components to facilitate ease of milling during plug removal. Of the nonmetallic materials used, commonly filament and convolute-wound composites are used. These wound materials have high hoop strengths, making them well suited for cylindrical, load-bearing components such as cones and mandrels. 
         [0004]    In conventional systems, filament and convolute-wound composites are made by winding around a solid wrapping mandrel. The filament or sheet is coated with resin prior to application onto the wrapping mandrel and successively layered until the desired dimensions are achieved. Once the part is complete, it is cured and the wrapping mandrel is removed. The resulting part is extremely strong, relatively cheap, and quick to manufacture. 
         [0005]    Due to the manufacturing process required to make these wound components, parts with solid inner diameters cannot be made. This is generally not an issue for frac plugs where flow area through the inner diameter (“ID”) is desired. However, most bridge plugs have functional requirements that necessitate a solid ID. As a result, corks or other mechanical components are installed in wound mandrels for bridge plugs to obstruct their IDs and allow them to act as “solid” components. Unfortunately, these corks may be problematic both in manufacturing, installation, and operation. 
         [0006]    Therefore, there is a need for an improved wound composite mandrel to improve manufacturing and installation, and to facilitate milling operations. 
       SUMMARY 
       [0007]    A bridge plug and a method for manufacturing the bridge plug are provided. The bridge plug may take the form of a millable bridge plug. The millable bridge plug may be constructed with an obstructed inner passage. The inner passage is obstructed by a member integrally positioned within the inner passage and about which composite material is wound. The obstruction is positioned within a mandrel of the bridge plug during manufacture of the mandrel. 
         [0008]    This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Description of the Invention section. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Furthermore, the claimed subject matter is not constrained to limitations that solve any or all disadvantages noted in any part of this disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Certain embodiments of the disclosure will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements. It should be understood; however, that the accompanying figures illustrate the various implementations described herein and are not meant to limit the scope of various technologies described herein. 
           [0010]      FIG. 1A  illustrates a solid mandrel about which composite material is wound, according to an aspect of this disclosure; 
           [0011]      FIG. 1B  is a cross-sectional view of the mandrel of  FIG. 1A , with layers of composite material wrapped about it, according to an aspect of this disclosure; 
           [0012]      FIG. 1C  illustrates withdrawal of the solid mandrel from the layers of the composite material of  FIG. 1B , according to an aspect of this disclosure; 
           [0013]      FIG. 1D  is a cross-sectional view of a composite tubular after withdrawal of the mandrel of  FIG. 1A , according to an aspect of this disclosure; 
           [0014]      FIG. 2A  illustrates independent segments of a multi-segment wrapping mandrel, according to an aspect of this disclosure; 
           [0015]      FIG. 2B  illustrates the independent segments of the multi-segment wrapping mandrel of  FIG. 2A  coupled together, according to an aspect of this disclosure; 
           [0016]      FIG. 2C  is a cross-sectional view of the multi-segment wrapping mandrel of  FIG. 2B  with composite material applied about the mandrel, according to an aspect of this disclosure; 
           [0017]      FIG. 2D  illustrates removal of segments of the multi-segment wrapping mandrel of  FIG. 2C , according to an aspect of this disclosure; and 
           [0018]      FIG. 2E  illustrates a composite tubular with a solid inner passageway after removal of independent segments, according to an aspect of this disclosure. 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0019]    The present disclosure generally relates to a system and methodology which facilitates construction of a millable bridge plug with an obstructed internal passageway. The bridge plug may be used for plugging of a wellbore during, for example, a fracturing operation. Aspects may generally include a true solid inner diameter (“ID”) design for bridge plugs constructed of, for example, filament and convolute-wound composite mandrels. As such, aspects may take the form of a manufacturing method which includes wrapping of a solid ID cylindrical components during a winding process. Aspects may simplify manufacture of the wound mandrel for a composite bridge plug. 
         [0020]      FIGS. 1A through 1D  illustrate a wrapping mandrel  100  comprising a single component. During a winding process, the wrapping mandrel  100  is wound with a composite material  102 . After the winding process is complete, the wrapping mandrel  100  is removed from the composite material  102  forming a cylindrical composite mandrel  104 . The composite mandrel  104  has a channel that extends therethrough formed by the wrapping mandrel  100 . 
         [0021]      FIGS. 2A through 2E  illustrate a wrapping mandrel  200  having multiple parts, including two wrapping mandrels  202  and  204  extending from a core or plug  206 . The core  206  may form a substantially solid piece and comprise a nonmetallic material. In an alternative aspect, the core  206  may comprise a metallic material. The nonmetallic core  206  may be configured to allow the wrapping mandrel  200  to form as one solid piece. Before the winding process, the two wrapping mandrels  202  and  204  are brought together around the solid core  206 . The two wrapping mandrels  202  and  204  sandwich the solid core  206  between them such that the solid core  206  is “squeezed” by the two wrapping mandrels  202  and  204 . The two wrapping mandrels  202  and  204  may squeeze the solid core  206  from opposing directions. During a winding process, the wrapping mandrel  200  is wound with a composite material  208 . After winding is complete, the two parts  202  and  204  of the wrapping mandrel  200  may be separated and removed, leaving a mandrel  210  with the solid core  206  inlaid. The mandrel  210  may have the structural properties of a wound part but with the solid ID, which is not achievable using conventional winding processes. The term “substantially” is intended to mean considerable in extent or largely but not necessarily wholly that which is specified. 
         [0022]    The two part wrapping mandrel  200  may be implemented instead of a single piece wrapping mandrel. Any suitable attachment mechanism may be implemented to attach the two wrapping mandrels  202  and  204  to the solid core  206 . For example, the two wrapping mandrels  202  and  204  may be attached by a threaded interface, a mechanical interference, a friction fit, or still other attachment mechanisms. The two wrapping mandrels  202  and  204  may have a substantially cylindrical shape. 
         [0023]    The resulting mandrel  210  may include an outer mandrel member  212  and the plug  206 . The outer mandrel member  212  has an inner surface  214  that defines a channel that extends from a first end  216  to a second end  218 . 
         [0024]    The plug  206  is positioned within the channel between the first end  216  and the second end  218 . The plug  206  contacts the inner surface  214  at a plug interface  220 . In an aspect, the plug interface  220  is located in a center between the first end  216  and the second end  218 . In alternative aspects, the plug interface  220  may be located at various locations within the channel between the first end  216  and the second end  218 . 
         [0025]    The inner surface  214  has a first inner diameter, a second inner diameter, and an interface diameter. The first inner diameter is a diameter of the channel between the first end  216  and the plug interface  220 . The second inner diameter is a diameter of the channel between the plug interface  220  and the second end  218 . In an aspect, the first inner diameter is substantially equal to the second inner diameter. The interface diameter is a diameter at the plug interface  220 . The interface diameter is greater than the first inner diameter and the second inner diameter. 
         [0026]    The plug  206  may have a biconic shape, rhombohedron shape, rectangular prism shape, or other suitable shape to substantially prevent fluid flow through the channel of the outer mandrel member  212 . 
         [0027]    The winding process may begin after the two wrapping mandrels  202  and  204  are attached to the plug  206 . The two wrapping mandrels  202  and  204  may comprise steel, or other suitable material for winding. The two wrapping mandrels  202  and  204  may be coated with a coating material (not shown) to prevent resin and fibers of the composite material  208  from adhering during the winding process. The coating allows the two wrapping mandrels  202  and  204  to be removed after the winding process is complete. In alternative aspects, other methods may be used to prevent resin and fibers from adhering to the two wrapping mandrels  202  and  204 , such as treating the surfaces of the wrapping mandrels  202  and  204 , modifying the geometry of the wrapping mandrels  202  and  204  to facilitate removal, or still other methods. In still other alternative aspects, an outer surface of the plug  206  may be roughened and/or include a coating (e.g. adhesive) to prevent movement of the plug  206  within the channel of the outer mandrel member  212 . The roughed surface and/or adhesive coating of the plug  206  provides a seal between the plug  206  and the resin and fiber layers wound around the plug  206 , and may facilitate the removal of the wrapping mandrels  202  and  204  after the winding process is complete. During the winding process, the outer mandrel member  212  is formed by the resin and fibers, and the interface  220  is formed between the plug  206  and outer mandrel member  212  that provides a “fluid-tight” seal, substantially preventing any fluid from flowing through the channel of the of the outer mandrel member  212 . 
         [0028]    After winding the composite material  208  about the wrapping mandrel  200 , a curing or postbake operation may be performed to enhance physical and structural characteristics of the composite material  208  to increase performance. The curing operation may be performed as appropriate depending on desired physical or structural characteristics. It will be appreciated that consideration may be made to ensure that the material properties of the plug  206  are not negatively affected by the temperature exposure during the curing process. Specifically, curing and/or postbaking may be conducted to avoid changing the material properties of the plug  206 . In some embodiments, the materials of the plug  206  may be selected to withstand curing and/or postbaking. 
         [0029]    After the curing or postbake operation is complete, any mechanical interface between the plug  206  and the two wrapping mandrels  202  and  204  may be broken and the two wrapping mandrels  202  and  204  may be removed. The resulting part is a structurally-sound composite tubular mandrel  210  with a solid ID formed by the plug  206  within the tubular outer mandrel member  212 . 
         [0030]    The mandrel  210  may be used in a bridge plug or other tool. Depending on the application, the bridge plug may have a variety of configurations and/or components including, for example, a seal, a lower slip, and an upper slip. The seal and the lower and upper slips are configured to selectively actuate into sealing engagement with an inner surface of the wellbore. The size and shape of the various components of the bridge plug may also be adjusted or selected according to the parameters of a given application. 
         [0031]    These specific embodiments described above are for illustrative purposes and are not intended to limit the scope of the disclosure as otherwise described and claimed herein. Modification and variations from the described embodiments exist. The scope of the invention is defined by the appended claims.