You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND 
       [0001]    It is desirable at times to plug tubular systems that are employed to transport fluids. In the downhole industry, for example, operators inject matter referred to as “junk shot” into leaking wellbores to plug the leak. Junk shot is commonly made of ground up tires and metal balls. Although such material often works adequately for its intended purpose, operators are always interested in new devices and methods to improve the art. 
       BRIEF DESCRIPTION 
       [0002]    Disclosed herein is plug-inducing matter which includes junk shot comprising members and swellable material substantially covering the members which are configured to swell upon exposure to wellbore fluids. 
         [0003]    Also disclosed is a method of plugging a leaking wellbore including injecting junk shot having members covered by swellable material that is swellable in wellbore fluids into a leaking wellbore, exposing the swellable material to wellbore fluids, and swelling the swellable material. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]    The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike: 
           [0005]      FIG. 1  depicts a cross sectional view of a piece of junk shot disclosed herein; and 
           [0006]      FIG. 2  depicts a cross sectional view of an alternate embodiment of a piece of junk shot disclosed herein. 
       
    
    
     DETAILED DESCRIPTION 
       [0007]    A detailed description of one or more embodiments of the disclosed apparatus and method are presented herein by way of exemplification and not limitation with reference to the Figures. 
         [0008]    Referring to  FIG. 1 , plug-inducing matter referred to as junk shot disclosed herein is illustrated at  10 . The junk shot  10  includes, a member  14  that is covered by a swellable material  18 . Although the junk shot  10  illustrated in this embodiment is spherical the invention is not be limited to such a configuration as other shapes are contemplated. Optionally the member  10  may be bonded to the swellable material  18  at an interface  22  therebetween by an adhesive  26  or other means of generating attachment therebetween. 
         [0009]    The member  14 , in embodiments disclosed herein is substantially non-swellable, and may be constructed of phenolic, such as is commonly used for tripping balls in the downhole industry, or other materials such as, iron, lead, bismuth, ceramic and glass. It may be desirable to employ a material for the member  14  that has a density comparable to the density of fluid that the junk shot  10  will be injected within to facilitate placement of the junk shot  10  to the desired location. In other applications it may be desirable to employ members  14  having greater density than a target fluid so that the junk shot  10  will tend to sink therewithin. In a hydrocarbon recovery application, for example, where heavy muds and drilling fluids are employed, using a more dense material such as lead or bismuth for the member  14  can make transporting the junk shot  10  to the location of the leak to be sealed an easier task. 
         [0010]    The fluid in which the swellable material  18  needs to swell influences material selection for the swellable material  18 . As such, for applications in which the target fluid is well defined the swellable material  18  can be tailored specifically to that target fluid. Generally, for wellbore fluids such as water, brine, hydrocarbons, drilling mud, or combinations of these a material that will swell in either an aqueous or a non-aqueous medium or both is preferred. Materials disclosed in U.S. Patent Application 2010/0147507, the content of which is incorporated by reference herein in its entirety, meet these specific criteria for use as the swellable material  18 . The &#39;507 reference discloses use of a rubber compound based on a base polymer of EPDM (e.g., ethylene propylene diene monomer rubber) or Nitrile with an acrylic copolymer added that can volumetrically swell un bonded as much as 250-300% in refined oil or water respectively. Since swelling materials to these levels can weaken the material significantly, using a compound/material that swells when bonded in the range of 5-35% may be more desirable for the swellable material  18  that covers the member  14 . 
         [0011]    In addition to the materials employed for the member  14  and the swellable material  18 , sizes of the junk shot  10  also influence mobility and sealing effectiveness thereof In wellbore applications a maximum radial dimension  30  of between ¾ to about ¼ inches for the junk shot  10  may provide the mobility and sealing effect desired. Accordingly, the foregoing maximum radial dimension  30  of the junk shot  10  can well accommodate a maximum radial dimension  34  of the member  14  of between ½ to ¾ of an inch. 
         [0012]    Additionally, the junk shot  10  can include pieces  38 , or chunks, of the swellable material  18  that do not have the member  14  encased therein. The pieces  38  can have well defined shapes, such as spherical, cubic, elliptical, etc, or can have random shapes such as may be generated from grinding or tearing the pieces  38  from a larger portion of the swellable material  18 . Employing a maximum radial dimension  42  of between 1 and 1 1/4 inches for the pieces  38  may maintain a desired distribution of the pieces  38  within the junk shot  10  during transport to assure the pieces  38  aid in plugging a leak. Additionally, since the pieces  38  do not include a member  14  may be configured to swell unbonded in the range of 10-100% volumetrically for best results. 
         [0013]    While the invention has been described with reference to an exemplary embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the claims. Also, in the drawings and the description, there have been disclosed exemplary embodiments of the invention and, although specific terms may have been employed, they are unless otherwise stated used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention therefore not being so limited. Moreover, the use of the terms first, second, etc. do not denote any order or importance, but rather the terms first, second, etc. are used to distinguish one element from another. Furthermore, the use of the terms a, an, etc. do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item.

Summary:
Plug-inducing matter includes junk shot comprising members and swellable material substantially covering the members which are configured to swell upon exposure to wellbore fluids.