Abstract:
An apparatus and a technique related to a composite member of two different composite materials is disclosed. Aspects include a technique which may include forming a first portion using a first composite material and forming a second portion molding a second composite material over the first portion. Aspects further include a millable frac or bridge plug may be created.

Description:
CROSS-REFERENCE 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 62/326,970, filed on Apr. 25, 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]    Molded phenolic is a material used due its ease of milling, relatively high shear, and bearing strength, and it can be molded into a final form. This makes complex geometry more economic at the production scale than materials that are machined to final form (i.e. wound composites). 
       SUMMARY 
       [0005]    An apparatus and a method for manufacturing the apparatus are provided. The apparatus may take the form of a millable bridge plug. In some aspects, a method may include manufacturing a composite member of two different composite materials. The technique may include forming a first portion using a first composite material and forming a second portion by molding a second composite material over the first portion. The first composite material is different from the second composite material. The first portion may be formed by a winding process, and the second portion may be formed by a molding process. 
         [0006]    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 
         [0007]    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. 
           [0008]      FIG. 1  illustrates a wound composite part around a mandrel, according to an aspect of this disclosure; 
           [0009]      FIG. 2  illustrates the wound composite part shown in  FIG. 1  positioned within a mold in a first position, according to an aspect of this disclosure; 
           [0010]      FIG. 3  illustrates the would composite part shown in  FIG. 1  positioned within a mold in a second position, according to an aspect of this disclosure; 
           [0011]      FIG. 4  illustrates a wound composite with a molded outer shell, according to an aspect of this disclosure; and 
           [0012]      FIG. 5  illustrates a composite plug lower cone, according to an aspect of this disclosure. 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0013]    In the following description, numerous details are set forth to provide an understanding of some aspects of the present disclosure. However, it will be understood by those of ordinary skill in the art that the system and/or methodology may be practiced without these details and that numerous variations or modifications from the described aspects may be possible. 
         [0014]    Certain terminology is used in the description for convenience only and is not limiting. The words “top”, “bottom”, “above,” and “below” designate directions in the drawings to which reference is made. The term “substantially” is intended to mean considerable in extent or largely but not necessarily wholly that which is specified. The terminology includes the above-listed words, derivatives thereof and words of similar import. 
         [0015]    Typically, when designing a frac or bridge plug component, one selects a material based on a desired functionality. However, some components could benefit from the advantages provided by both a molded phenolic and a wound composite. Making components out of both materials could increase functionality and/or decrease cost. Table 1 below lists some examples of possible advantages and disadvantages of the wound composites and molded fiber phenolic materials. 

 
         [0016]    In conventional systems, frac or bridge plug components that are small in overall volume, require complex geometries or features, and/or do not have a functional requirement for high hoop strength, are typically made of molded composite. Components that are large in overall volume, have simple geometries, and/or in which have a functional requirement for a high hoop strength, are typically made of wound composite and machined to a final shape. 
         [0017]    Complex components of millable frac plugs, in which a large hoop strength is desired, are typically made out of a wound composite and machined to final form. This can be problematic for complex components at a production scale due to the cost of machining complex geometries. If the component was molded, the production price of that component would be mostly independent of geometric complexity. For many components, molded phenolic does not have the hoop strength desired for particular applications, preventing these parts from being molded to final form. 
         [0018]    Aspects described herein include a manufacturing method to enable a composite frac plug component to be formed out of both molded fiber phenolic and wound composite. Benefits of the composite frac plug include providing 1.) a low volumetric cost of wound composite and a low manufacturing cost of molded phenolic, and 2.) a high hoop strength of wound composite and high bearing/shear strength of molded composite. A performance benefit of both materials may be achieved without negatively affecting part cost. 
         [0019]    The composite frac plug component may include a core of wound composite, which provides the frac plug component with the strength advantages of a wound composite. One aspect may include winding a composite cylinder that provides structural strength with minimal machining or surface features desired. The wound cylinder could make up the bulk of the volume, thereby reducing molded material costs. A phenolic shell may be molded over the wound cylinder to achieve a net-shape part. The molded material may be used to add complex features. In conventional systems, these features may have been machined otherwise. Additionally, the molded material may provide bearing and shear strength not achieved with the wound material alone. 
         [0020]      FIGS. 1 through 5  illustrate several steps for manufacturing a composite frac plug having both molded fiber phenolic material and a wound composite.  FIG. 1  illustrates a winding process, which includes winding a composite material about a winding mandrel  5  to form a wound composite member  10 . In an aspect, the winding process may include a conventional filament or convolute-wound process. The winding mandrel  5  rotates about an axis A. In an aspect, axis A extends through a center of the mandrel  5 . The composite member  10  may include a minimal number of features, and may primarily form a cylindrical tube-like structure. 
         [0021]      FIG. 2  illustrates the wound composite member  10  positioned within a two piece mold  20 . The two piece mold  20  may include an upper mold  22  and a lower mold  24 . The two piece mold  20  is in an open position, whereby the upper mold  22  is spaced apart from the lower mold  24 . Each of the upper and lower molds  22  and  24  may include a molded composite preform  30  within. 
         [0022]      FIG. 3  illustrates the two piece mold  20  in a closed position, whereby the upper mold  22  and the lower mold  24  are compressed towards each other. During compression, the wound composite member  10  may be fully encapsulated by the molded composite material  30 . 
         [0023]      FIG. 4  illustrates a final composite frac plug  40  comprising the wound composite member  10  at its core and the molded composite material  30  formed about the wound composite member  10 . The resulting composite frac plug  40  may be predominantly made of wound composite by volume. The raw composite material is generally cheaper than molded phenolic, which makes the resulting composite frac plug  40  cheaper to manufacture. The composite frac plug  40  retains an overall hoop strength similar to that of a part made of wound composite. Furthermore, complex geometries may be molded onto the final shape of the frac plug  40 , allowing difficult-to-machine features to be added. This results in a frac plug  40  that is cheaper to manufacture at the production scale. 
         [0024]      FIG. 5  illustrates an example of a feature molded onto the frac plug  40 , according to an aspect of this disclosure. A complex geometry that may be molded to the final shape and that also has a high hoop strength may include, for example, a lower cone  100  of a composite frac/bridge plug. The composite plug lower cone  100  may comprise a hybrid composite material with filament or convolute-wound core  102  with a molded composite shell  104 . 
         [0025]    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.