Patent Publication Number: US-10767442-B2

Title: Flow control in subterranean wells

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 15/138,685 filed on 26 Apr. 2016, which is: a) a continuation-in-part of U.S. application Ser. No. 14/698,578 filed on 28 Apr. 2015, b) a continuation-in-part of International application serial no. PCT/US15/38248 filed on 29 Jun. 2015, and c) claims the benefit of the filing date of U.S. provisional application Ser. No. 62/252,174 filed on 6 Nov. 2015. The entire disclosures of these prior applications are incorporated herein by this reference. 
    
    
     BACKGROUND 
     This disclosure relates generally to equipment utilized and operations performed in conjunction with a subterranean well and, in one example described below, more particularly provides for flow control in wells. 
     It can be beneficial to be able to control how and where fluid flows in a well. For example, it may be desirable in some circumstances to be able to prevent fluid from flowing into a particular formation zone. As another example, it may be desirable in some circumstances to cause fluid to flow into a particular formation zone, instead of into another formation zone. Therefore, it will be readily appreciated that improvements are continually needed in the art of controlling fluid flow in wells. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a representative partially cross-sectional view of an example of a well system and associated method which can embody principles of this disclosure. 
         FIGS. 2A-D  are enlarged scale representative partially cross-sectional views of steps in an example of a re-completion method that may be practiced with the system of  FIG. 1 . 
         FIGS. 3A-D  are representative partially cross-sectional views of steps in another example of a method that may be practiced with the system of  FIG. 1 . 
         FIGS. 4A  &amp; B are enlarged scale representative elevational views of examples of a flow conveyed device that may be used in the system and methods of  FIGS. 1-3D , and which can embody the principles of this disclosure. 
         FIG. 5  is a representative elevational view of another example of the flow conveyed device. 
         FIGS. 6A  &amp; B are representative partially cross-sectional views of the flow conveyed device in a well, the device being conveyed by flow in  FIG. 6A , and engaging a casing opening in  FIG. 6B . 
         FIGS. 7-9  are representative elevational views of examples of the flow conveyed device with a retainer. 
         FIG. 10  is a representative partially cross-sectional view of another method that can embody the principles of this disclosure. 
         FIGS. 11A-E  are representative flowcharts for additional examples of methods that can embody the principles of this disclosure. 
         FIGS. 12 &amp; 13  are representative cross-sectional views of additional examples of the flow conveyed device. 
         FIG. 14  is a representative cross-sectional view of a well tool that may be operated using the flow conveyed device. 
     
    
    
     DETAILED DESCRIPTION 
     Representatively illustrated in  FIG. 1  is a system  10  for use with a well, and an associated method, which can embody principles of this disclosure. However, it should be clearly understood that the system  10  and method are merely one example of an application of the principles of this disclosure in practice, and a wide variety of other examples are possible. Therefore, the scope of this disclosure is not limited at all to the details of the system  10  and method described herein and/or depicted in the drawings. 
     In the  FIG. 1  example, a tubular string  12  is conveyed into a wellbore  14  lined with casing  16  and cement  18 . Although multiple casing strings would typically be used in actual practice, for clarity of illustration only one casing string  16  is depicted in the drawings. 
     Although the wellbore  14  is illustrated as being vertical, sections of the wellbore could instead be horizontal or otherwise inclined relative to vertical. Although the wellbore  14  is completely cased and cemented as depicted in  FIG. 1 , any sections of the wellbore in which operations described in more detail below are performed could be uncased or open hole. Thus, the scope of this disclosure is not limited to any particular details of the system  10  and method. 
     The tubular string  12  of  FIG. 1  comprises coiled tubing  20  and a bottom hole assembly  22 . As used herein, the term “coiled tubing” refers to a substantially continuous tubing that is stored on a spool or reel  24 . The reel  24  could be mounted, for example, on a skid, a trailer, a floating vessel, a vehicle, etc., for transport to a wellsite. Although not shown in  FIG. 1 , a control room or cab would typically be provided with instrumentation, computers, controllers, recorders, etc., for controlling equipment such as an injector  26  and a blowout preventer stack  28 . 
     As used herein, the term “bottom hole assembly” refers to an assembly connected at a distal end of a tubular string in a well. It is not necessary for a bottom hole assembly to be positioned or used at a “bottom” of a hole or well. 
     When the tubular string  12  is positioned in the wellbore  14 , an annulus  30  is formed radially between them. Fluid, slurries, etc., can be flowed from surface into the annulus  30  via, for example, a casing valve  32 . One or more pumps  34  may be used for this purpose. Fluid can also be flowed to surface from the wellbore  14  via the annulus  30  and valve  32 . 
     Fluid, slurries, etc., can also be flowed from surface into the wellbore  14  via the tubing  20 , for example, using one or more pumps  36 . Fluid can also be flowed to surface from the wellbore  14  via the tubing  20 . 
     In the further description below of the examples of  FIGS. 2A-9 , one or more flow conveyed devices are used to block or plug openings in the system  10  of  FIG. 1 . However, it should be clearly understood that these methods and the flow conveyed device may be used with other systems, and the flow conveyed device may be used in other methods in keeping with the principles of this disclosure. 
     The example methods described below allow existing fluid passageways to be blocked permanently or temporarily in a variety of different applications. Certain flow conveyed device examples described below are made of a fibrous material and comprise a central body, a “knot” or other enlarged geometry. Other flow control device examples may not be made of a fibrous material, may not have a centrally positioned body, and/or may not comprise a knot. 
     The devices are conveyed into leak paths using pumped fluid. Fibrous material extending outwardly from a body of a device can “find” and follow the fluid flow, pulling the enlarged geometry into a restricted portion of a flow path, causing the enlarged geometry and additional strands to become tightly wedged into the flow path thereby sealing off fluid communication. 
     The devices can be made of degradable or non-degradable materials. The degradable materials can be either self-degrading, or can require degrading treatments, such as, by exposing the materials to certain acids, certain base compositions, certain chemicals, certain types of radiation (e.g., electromagnetic or “nuclear”), or elevated temperature. The exposure can be performed at a desired time using a form of well intervention, such as, by spotting or circulating a fluid in the well so that the material is exposed to the fluid. 
     In some examples, the material can be an acid degradable material (e.g., nylon, etc.), a mix of acid degradable material (for example, nylon fibers mixed with particulate such as calcium carbonate), self-degrading material (e.g., poly-lactic acid (PLA), poly-glycolic acid (PGA), etc.), material that degrades by galvanic action (such as, magnesium alloys, aluminum alloys, etc.), a combination of different self-degrading materials, or a combination of self-degrading and non-self-degrading materials. 
     Multiple materials can be pumped together or separately. For example, nylon and calcium carbonate could be pumped as a mixture, or the nylon could be pumped first to initiate a seal, followed by calcium carbonate to enhance the seal. 
     In certain examples described below, the device can be made of knotted fibrous materials. Multiple knots can be used with any number of loose ends. The ends can be frayed or un-frayed. The fibrous material can be rope, fabric, cloth or another woven or braided structure. 
     The device can be used to block open sleeve valves, perforations or any leak paths in a well (such as, leaking connections in casing, corrosion holes, etc.). An opening in a well tool, whether formed intentionally or inadvertently, can be blocked using the device. Any opening through which fluid flows can be blocked with a suitably configured device. 
     In one example method described below, a well with an existing perforated zone can be re-completed. Devices (either degradable or non-degradable) are conveyed by flow to plug all existing perforations. 
     The well can then be re-completed using any desired completion technique. If the devices are degradable, a degrading treatment can then be placed in the well to open up the plugged perforations (if desired). 
     In another example method described below, multiple formation zones can be perforated and fractured (or otherwise stimulated, such as, by acidizing) in a single trip of the bottom hole assembly  22  into the well. In the method, one zone is perforated, the zone is fractured or otherwise stimulated, and then the perforated zone is plugged using one or more devices. 
     These steps are repeated for each additional zone, except that a last zone may not be plugged. All of the plugged zones are eventually unplugged by waiting a certain period of time (if the devices are self-degrading), by applying an appropriate degrading treatment, or by mechanically removing the devices. 
     Referring specifically now to  FIGS. 2A-D , steps in an example of a method in which the bottom hole assembly  22  of  FIG. 1  can be used in re-completing a well are representatively illustrated. In this method (see  FIG. 2A ), the well has existing perforations  38  that provide for fluid communication between an earth formation zone  40  and an interior of the casing  16 . However, it is desired to re-complete the zone  40 , in order to enhance the fluid communication. 
     Referring additionally now to  FIG. 2B , the perforations  38  are plugged, thereby preventing flow through the perforations into the zone  40 . Plugs  42  in the perforations can be flow conveyed devices, as described more fully below. In that case, the plugs  42  can be conveyed through the casing  16  and into engagement with the perforations  38  by fluid flow  44 . 
     Referring additionally now to  FIG. 2C , new perforations  46  are formed through the casing  16  and cement  18  by use of an abrasive jet perforator  48 . In this example, the bottom hole assembly  22  includes the perforator  48  and a circulating valve assembly  50 . Although the new perforations  46  are depicted as being formed above the existing perforations  38 , the new perforations could be formed in any location in keeping with the principles of this disclosure. 
     Note that other means of providing perforations  46  may be used in other examples. Explosive perforators, drills, etc., may be used if desired. The scope of this disclosure is not limited to any particular perforating means, or to use with perforating at all. 
     The circulating valve assembly  50  controls flow between the coiled tubing  20  and the perforator  48 , and controls flow between the annulus  30  and an interior of the tubular string  12 . Instead of conveying the plugs  42  into the well via flow  44  through the interior of the casing  16  (see  FIG. 2B ), in other examples the plugs could be deployed into the tubular string  12  and conveyed by fluid flow  52  through the tubular string prior to the perforating operation. In that case, a valve  54  of the circulating valve assembly  50  could be opened to allow the plugs  42  to exit the tubular string  12  and flow into the interior of the casing  16  external to the tubular string. 
     Referring additionally now to  FIG. 2D , the zone  40  has been fractured or otherwise stimulated by applying increased pressure to the zone after the perforating operation. Enhanced fluid communication is now permitted between the zone  40  and the interior of the casing  16 . 
     Note that fracturing is not necessary in keeping with the principles of this disclosure. Although certain examples described herein utilize fracturing, it should be understood that other types of stimulation operations (such as acidizing) may be performed instead of, or in addition to, fracturing. 
     In the  FIG. 2D  example, the plugs  42  prevent the pressure applied to fracture the zone  40  via the perforations  46  from leaking into the zone via the perforations  38 . The plugs  42  may remain in the perforations  38  and continue to prevent flow through the perforations, or the plugs may degrade, if desired, so that flow is eventually permitted through the perforations. 
     In other examples, fractures may be formed via the existing perforations  38 , and no new perforations may be formed. In one technique, pressure may be applied in the casing  16  (e.g., using the pump  34 ), thereby initially fracturing the zone  40  via some of the perforations  38  that receive most of the fluid flow  44 . After the initial fracturing of the zone  40 , and while the fluid is flowed through the casing  16 , plugs  42  can be released into the casing, so that the plugs seal off those perforations  38  that are receiving most of the fluid flow. 
     In this way, the fluid  44  will be diverted to other perforations  38 , so that the zone  40  will also be fractured via those other perforations  38 . The plugs  42  can be released into the casing  16  continuously or periodically as the fracturing operation progresses, so that the plugs gradually seal off all, or most, of the perforations  38  as the zone  40  is fractured via the perforations. That is, at each point in the fracturing operation, the plugs  42  will seal off those perforations  38  through which most of the fluid flow  44  passes, which are the perforations via which the zone  40  has been fractured. 
     Referring additionally now to  FIGS. 3A-D , steps in another example of a method in which the bottom hole assembly  22  of  FIG. 1  can be used in completing multiple zones  40   a - c  of a well are representatively illustrated. The multiple zones  40   a - c  are each perforated and fractured during a single trip of the tubular string  12  into the well. 
     In  FIG. 3A , the tubular string  12  has been deployed into the casing  16 , and has been positioned so that the perforator  48  is at the first zone  40   a  to be completed. The perforator  48  is then used to form perforations  46   a  through the casing  16  and cement  18 , and into the zone  40   a.    
     In  FIG. 3B , the zone  40   a  has been fractured by applying increased pressure to the zone via the perforations  46   a . The fracturing pressure may be applied, for example, via the annulus  30  from the surface (e.g., using the pump  34  of  FIG. 1 ), or via the tubular string  12  (e.g., using the pump  36  of  FIG. 1 ). The scope of this disclosure is not limited to any particular fracturing means or technique, or to the use of fracturing at all. 
     After fracturing of the zone  40   a , the perforations  46   a  are plugged by deploying plugs  42   a  into the well and conveying them by fluid flow into sealing engagement with the perforations. The plugs  42   a  may be conveyed by flow  44  through the casing  16  (e.g., as in  FIG. 2B ), or by flow  52  through the tubular string  12  (e.g., as in  FIG. 2C ). 
     The tubular string  12  is repositioned in the casing  16 , so that the perforator  48  is now located at the next zone  40   b  to be completed. The perforator  48  is then used to form perforations  46   b  through the casing  16  and cement  18 , and into the zone  40   b . The tubular string  12  may be repositioned before or after the plugs  42   a  are deployed into the well. 
     In  FIG. 3C , the zone  40   b  has been fractured by applying increased pressure to the zone via the perforations  46   b . The fracturing pressure may be applied, for example, via the annulus  30  from the surface (e.g., using the pump  34  of  FIG. 1 ), or via the tubular string  12  (e.g., using the pump  36  of  FIG. 1 ). 
     After fracturing of the zone  40   b , the perforations  46   b  are plugged by deploying plugs  42   b  into the well and conveying them by fluid flow into sealing engagement with the perforations. The plugs  42   b  may be conveyed by flow  44  through the casing  16 , or by flow  52  through the tubular string  12 . 
     The tubular string  12  is repositioned in the casing  16 , so that the perforator  48  is now located at the next zone  40   c  to be completed. The perforator  48  is then used to form perforations  46   c  through the casing  16  and cement  18 , and into the zone  40   c . The tubular string  12  may be repositioned before or after the plugs  42   b  are deployed into the well. 
     In  FIG. 3D , the zone  40   c  has been fractured by applying increased pressure to the zone via the perforations  46   c . The fracturing pressure may be applied, for example, via the annulus  30  from the surface (e.g., using the pump  34  of  FIG. 1 ), or via the tubular string  12  (e.g., using the pump  36  of  FIG. 1 ). 
     In some examples, the perforations  46   c  could be plugged after the zone  40   c  is fractured or otherwise stimulated. For example, such plugging of the perforations  46   c  could be performed in order to verify that the plugs are effectively blocking flow from the casing  16  to the zones  40   a - c.    
     The plugs  42   a,b  are then degraded and no longer prevent flow through the perforations  46   a,b . Thus, as depicted in  FIG. 3D , flow is permitted between the interior of the casing  16  and each of the zones  40   a - c.    
     The plugs  42   a,b  may be degraded in any manner. The plugs  42   a,b  may degrade in response to application of a degrading treatment, in response to passage of a certain period of time, or in response to exposure to elevated downhole temperature. The degrading treatment could include exposing the plugs  42   a,b  to a particular type of radiation, such as electromagnetic radiation (e.g., light having a certain wavelength or range of wavelengths, gamma rays, etc.) or “nuclear” particles (e.g., gamma, beta, alpha or neutron). 
     The plugs  42   a,b  may degrade by galvanic action or by dissolving. The plugs  42   a,b  may degrade in response to exposure to a particular fluid, either naturally occurring in the well (such as water or hydrocarbon fluid), or introduced therein (such as a fluid having a particular pH). 
     Note that any number of zones may be completed in any order in keeping with the principles of this disclosure. The zones  40   a - c  may be sections of a single earth formation, or they may be sections of separate formations. 
     In other examples, the plugs  42  may not be degraded. The plugs  42  could instead be mechanically removed, for example, by milling or otherwise cutting the plugs  42  away from the perforations, or by grabbing and pulling the plugs from the perforations. In any of the method examples described above, after the fracturing or other stimulating operation(s) are completed, the plugs  42  can be milled off or otherwise removed from the perforations  38 ,  46 ,  46   a,b  without dissolving, melting, dispersing or otherwise degrading a material of the plugs. 
     Referring additionally now to  FIG. 4A , an example of a flow conveyed device  60  that can incorporate the principles of this disclosure is representatively illustrated. The device  60  may be used for any of the plugs  42 ,  42   a,b  in the method examples described above, or the device may be used in other methods. 
     The device  60  example of  FIG. 4A  includes multiple fibers  62  extending outwardly from an enlarged body  64 . As depicted in  FIG. 4A , each of the fibers  62  has a lateral dimension (e.g., a thickness or diameter) that is substantially smaller than a size (e.g., a thickness or diameter) of the body  64 . 
     The body  64  can be dimensioned so that it will effectively engage and seal off a particular opening in a well. For example, if it is desired for the device  60  to seal off a perforation in a well, the body  64  can be formed so that it is somewhat larger than a diameter of the perforation. If it is desired for multiple devices  60  to seal off multiple openings having a variety of dimensions (such as holes caused by corrosion of the casing  16 ), then the bodies  64  of the devices can be formed with a corresponding variety of sizes. 
     In the  FIG. 4A  example, the fibers  62  are joined together (e.g., by braiding, weaving, cabling, etc.) to form lines  66  that extend outwardly from the body  64 . In this example, there are two such lines  66 , but any number of lines (including one) may be used in other examples. 
     The lines  66  may be in the form of one or more ropes, in which case the fibers  62  could comprise frayed ends of the rope(s). In addition, the body  64  could be formed by one or more knots in the rope(s). In some examples, the body  64  can comprise a fabric or cloth, the body could be formed by one or more knots in the fabric or cloth, and the fibers  62  could extend from the fabric or cloth. 
     In the  FIG. 4A  example, the body  64  is formed by a double overhand knot in a rope, and ends of the rope are frayed, so that the fibers  62  are splayed outward. In this manner, the fibers  62  will cause significant fluid drag when the device  60  is deployed into a flow stream, so that the device will be effectively “carried” by, and “follow,” the flow. 
     However, it should be clearly understood that other types of bodies and other types of fibers may be used in other examples. The body  64  could have other shapes, the body could be hollow or solid, and the body could be made up of one or multiple materials. The fibers  62  are not necessarily joined by lines  66 , and the fibers are not necessarily formed by fraying ends of ropes or other lines. Thus, the scope of this disclosure is not limited to the construction, configuration or other details of the device  60  as described herein or depicted in the drawings. 
     Referring additionally now to  FIG. 4B , another example of the device  60  is representatively illustrated. In this example, the device  60  is formed using multiple braided lines  66  of the type known as “mason twine.” The multiple lines  66  are knotted (such as, with a double or triple overhand knot or other type of knot) to form the body  64 . Ends of the lines  66  are not necessarily be frayed in these examples, although the lines do comprise fibers (such as the fibers  62  described above). 
     Referring additionally now to  FIG. 5 , another example of the device  60  is representatively illustrated. In this example, four sets of the fibers  62  are joined by a corresponding number of lines  66  to the body  64 . The body  64  is formed by one or more knots in the lines  66 . 
       FIG. 5  demonstrates that a variety of different configurations are possible for the device  60 . Accordingly, the principles of this disclosure can be incorporated into other configurations not specifically described herein or depicted in the drawings. Such other configurations may include fibers joined to bodies without use of lines, bodies formed by techniques other than knotting, etc. 
     Referring additionally now to  FIGS. 6A  &amp; B, an example of a use of the device  60  of  FIG. 4  to seal off an opening  68  in a well is representatively illustrated. In this example, the opening  68  is a perforation formed through a sidewall  70  of a tubular string  72  (such as, a casing, liner, tubing, etc.). However, in other examples the opening  68  could be another type of opening, and may be formed in another type of structure. 
     The device  60  is deployed into the tubular string  72  and is conveyed through the tubular string by fluid flow  74 . The fibers  62  of the device  60  enhance fluid drag on the device, so that the device is influenced to displace with the flow  74 . 
     Note that the device  60  can be deployed into a section of the tubular string  72  that would be inaccessible to conventional plugs, such as bridge plugs. For example, the device  60  can be conveyed by the flow  74  to a section of the tubular string  72  below a restriction  75  (such as, a casing patch, or another type of restriction). 
     Since the flow  74  (or a portion thereof) exits the tubular string  72  via the opening  68 , the device  60  will be influenced by the fluid drag to also exit the tubular string via the opening  68 . As depicted in  FIG. 6B , one set of the fibers  62  first enters the opening  68 , and the body  64  follows. However, the body  64  is appropriately dimensioned, so that it does not pass through the opening  68 , but instead is lodged or wedged into the opening. In some examples, the body  64  may be received only partially in the opening  68 , and in other examples the body may be entirely received in the opening. 
     The body  64  may completely or only partially block the flow  74  through the opening  68 . If the body  64  only partially blocks the flow  74 , any remaining fibers  62  exposed to the flow in the tubular string  72  can be carried by that flow into any gaps between the body and the opening  68 , so that a combination of the body and the fibers completely blocks flow through the opening. 
     In another example, the device  60  may partially block flow through the opening  68 , and another material (such as, calcium carbonate, PLA or PGA particles) may be deployed and conveyed by the flow  74  into any gaps between the device and the opening, so that a combination of the device and the material completely blocks flow through the opening. 
     The device  60  may permanently prevent flow through the opening  68 , or the device may degrade to eventually permit flow through the opening. If the device  60  degrades, it may be self-degrading, or it may be degraded in response to any of a variety of different stimuli. Any technique or means for degrading the device  60  (and any other material used in conjunction with the device to block flow through the opening  68 ) may be used in keeping with the scope of this disclosure. 
     In other examples, the device  60  may be mechanically removed from the opening  68 . For example, if the body  64  only partially enters the opening  68 , a mill or other cutting device may be used to cut the body from the opening. 
     Referring additionally now to  FIGS. 7-9 , additional examples of the device  60  are representatively illustrated. In these examples, the device  60  is surrounded by, encapsulated in, molded in, or otherwise retained by, a retainer  80 . 
     The retainer  80  aids in deployment of the device  60 , particularly in situations where multiple devices are to be deployed simultaneously. In such situations, the retainer  80  for each device  60  prevents the fibers  62  and/or lines  66  from becoming entangled with the fibers and/or lines of other devices. 
     The retainer  80  could in some examples completely enclose the device  60 . In other examples, the retainer  80  could be in the form of a binder that holds the fibers  62  and/or lines  66  together, so that they do not become entangled with those of other devices. 
     In some examples, the retainer  80  could have a cavity therein, with the device  60  (or only the fibers  62  and/or lines  66 ) being contained in the cavity. In other examples, the retainer  80  could be molded about the device  60  (or only the fibers  62  and/or lines  66 ). 
     At least after deployment of the device  60  into the well, the retainer  80  dissolves, melts, disperses or otherwise degrades, so that the device is capable of sealing off an opening  68  in the well, as described above. For example, the retainer  80  can be made of a material  82  that degrades in a wellbore environment. 
     The retainer material  82  may degrade after deployment into the well, but before arrival of the device  60  at the opening  68  to be plugged. In other examples, the retainer material  82  may degrade at or after arrival of the device  60  at the opening  68  to be plugged. If the device  60  also comprises a degradable material, then preferably the retainer material  82  degrades prior to the device material. 
     The material  82  could, in some examples, melt at elevated wellbore temperatures. The material  82  could be chosen to have a melting point that is between a temperature at the earth&#39;s surface and a temperature at the opening  68 , so that the material melts during transport from the surface to the downhole location of the opening. 
     The material  82  could, in some examples, dissolve when exposed to wellbore fluid. The material  82  could be chosen so that the material begins dissolving as soon as it is deployed into the wellbore  14  and contacts a certain fluid (such as, water, brine, hydrocarbon fluid, etc.) therein. In other examples, the fluid that initiates dissolving of the material  82  could have a certain pH range that causes the material to dissolve. 
     Note that it is not necessary for the material  82  to melt or dissolve in the well. Various other stimuli (such as, passage of time, elevated pressure, flow, turbulence, etc.) could cause the material  82  to disperse, degrade or otherwise cease to retain the device  60 . The material  82  could degrade in response to any one, or a combination, of: passage of a predetermined period of time in the well, exposure to a predetermined temperature in the well, exposure to a predetermined fluid in the well, exposure to radiation in the well and exposure to a predetermined chemical composition in the well. Thus, the scope of this disclosure is not limited to any particular stimulus or technique for dispersing or degrading the material  82 , or to any particular type of material. 
     In some examples, the material  82  can remain on the device  60 , at least partially, when the device engages the opening  68 . For example, the material  82  could continue to cover the body  64  (at least partially) when the body engages and seals off the opening  68 . In such examples, the material  82  could advantageously comprise a relatively soft, viscous and/or resilient material, so that sealing between the device  60  and the opening  68  is enhanced. 
     Suitable relatively low melting point substances that may be used for the material  82  can include wax (e.g., paraffin wax, vegetable wax), ethylene-vinyl acetate copolymer (e.g., ELVAX™ available from DuPont), atactic polypropylene and eutectic alloys. Suitable relatively soft substances that may be used for the material  82  can include a soft silicone composition or a viscous liquid or gel. Suitable dissolvable materials can include PLA, PGA, anhydrous boron compounds (such as anhydrous boric oxide and anhydrous sodium borate), polyvinyl alcohol (PVA), polyvinyl acetate (PVAc), polyethylene oxide, salts and carbonates. 
     In  FIG. 7 , the retainer  80  is in a cylindrical form. The device  60  is encapsulated in, or molded in, the retainer material  82 . The fibers  62  and lines  66  are, thus, prevented from becoming entwined with the fibers and lines of any other devices  60 . 
     In  FIG. 8 , the retainer  80  is in a spherical form. In addition, the device  60  is compacted, and its compacted shape is retained by the retainer material  82 . A shape of the retainer  80  can be chosen as appropriate for a particular device  60  shape, in compacted or un-compacted form. A frangible coating  88  may be provided on the retainer  80 . 
     In  FIG. 9 , the retainer  80  is in a cubic form. Thus, any type of shape (polyhedron, spherical, cylindrical, etc.) may be used for the retainer  80 , in keeping with the principles of this disclosure. 
     In some examples, the devices  60  can be prepared from non-fibrous or nonwoven material, and the devices may or may not be knotted. The devices  60  can also be prepared from film, tube, or nonwoven fabric. The devices  60  may be prepared from a single sheet of material or multiple strips of sheet material. 
     Polyvinyl alcohol (PVA) and polyvinyl acetate (PVAc) are described above as suitable soluble retainer materials  82 , but these materials may be used for the device  60  itself (with or without the retainer  80 ). PVA is available with dissolution temperatures in water over a wide range (e.g., ambient temperature to 175° F.). PVA and PVAc can be used in the form of film, tube, and fiber or filament. 
     Some advantages of PVA include: 1) PVA can be formulated to be insoluble at a typically lowered circulating temperature during a fracturing operation, and later dissolve when heated to bottom hole static temperature. No additional treatment is required to remove the knot or other plugging device made with PVA. 2) PVA can be cross-linked with borate ion or aluminum ion to decrease its dissolution rate. 3) PVA properties can be modified by varying a degree of hydrolysis, copolymerization, or addition of plasticizer. 
     An example of a PVA knot device  60  can be formed as follows: A length of PVA tube (for example, a 4 inch (˜10 cm) width flat tube made from 3 mil (˜0.08 mm) M1030 PVA film available from MonoSol, LLC of Portage, Ind. USA) is turned halfway inside-out to form a double-walled tube. The tube is folded in half lengthwise and one end is pinched in a vise. The other end is connected to a vacuum pump to remove air from the tube. The resulting flattened tube is twisted into a tight strand. The resulting strand is tied in a triple overhand knot. The knot can be seated against a 0.42 inch (˜10.7 mm) diameter orifice and pressurized to 4500 psi (˜31 MPa) with water. The knot seals the orifice, completely shutting off the flow of water. 
     Another material suitable for use in the device  60  is an acid-resistant material that is water-soluble. Poly-methacrylic acid is insoluble at low pH, but dissolves at neutral pH. Devices  60  made from poly-methacrylic acid could be used as a diverter in an acid treatment to block treated perforations and divert the acid to other perforations. After the treatment is complete, the devices  60  would dissolve as the pH rises. No remedial treatment would be required to remove the plugs. 
     Referring additionally now to  FIG. 10 , an example of a method  100  of completing a well is representatively illustrated. In this method  100 , after stimulating the formation  40  via existing and/or new perforations  46 , flow through the perforations is blocked by plugging devices  60  released into the well. 
     However, not all of the perforations  46  are plugged by the devices  60 . Instead, some of the perforations  46  are intentionally left open, so that fluid can subsequently be flowed through the openings  68  of the open perforations, and into the formation  40 . 
     That is, some of the openings  68  of the perforations  46  are not blocked by the plugging devices  60 . One benefit of this is that flow  102  through the wellbore  14  can be used to convey well tools (such as, perforating gun  48 , logging tools, etc.) through the wellbore. 
     In this manner, new perforations can be formed in the well where desired (or other operations can be performed by other well tools). After the perforating or other operations are performed, any of the open perforations  46  (pre-existing or new) can be plugged with additional devices  60 , if desired. 
     Referring additionally now to  FIGS. 11A-E , flowcharts for various examples of a method  200  that can embody the principles of this disclosure are representatively illustrated. However, it should be clearly understood that the flow conveyed plugging devices  60  described herein may be used in methods and systems other than those described herein, in keeping with the scope of this disclosure. 
     In  FIG. 11A , the method  200  is performed with pre-existing, newly formed, or a combination of pre-existing and newly formed perforations (such as, any of perforations  38 ,  46 ,  46   a - c ). In step  202 , a treatment fluid is flowed into the perforations. The fluid may be a stimulation fluid, such as, a fracturing and/or an acidizing fluid, an inhibitor (for example, to inhibit paraffin, asphaltene or scale formation) or a remediation fluid (for example, to remove damage, such as scale, clay and polymer deposits). 
     One or more fractures may be formed as a result of the fluid flowing step  202 . The stimulation fluid flow may be represented by the flows  44 ,  74  in any of the examples described above, but the flow (e.g., direction, location, timing, etc.) is not limited to the above examples. 
     In step  204 , characteristics of fluid flow into the perforations is monitored (e.g., pressure, flow rate, etc.). This monitoring step  204  can be used to determine whether the perforations are receiving flow, whether and to what extent fractures have been formed, whether an acidizing treatment has been successful or how the treatment is progressing, and certain properties of the formation  40  (such as, damage, permeability, porosity, fracture pressure, closure pressure, etc.). If plugging devices  60  have been released into the well, the monitoring step  204  can be used to determine if, when and how many plugging devices have blocked flow into respective perforations, and whether additional plugging devices should be released into the well. 
     In step  206 , a decision is made whether to release plugging devices  60  into the well in step  208 , or to end the method  200 . If all or a desired quantity of the perforations have not been plugged, then plugging devices  60  can be released into the well in step  208 . 
     Note that it is not necessary for all perforations to be plugged. For example, in the method  100  depicted in  FIG. 10 , not all perforations are plugged, in order to allow for fluid flow  102  to convey a well tool (such as the perforating gun  48 ) through the wellbore  14 . 
     If plugging devices  60  have already been released into the well, then the step  206  decision can be whether to release additional plugging devices into the well. For example, if the flow monitoring step  204  indicates that a desired quantity of the perforations have not yet been plugged, then in step  206  the decision may be made to release additional plugging devices. 
     If plugging devices are released in step  208 , then in step  210  the plugging devices will preferentially plug the perforations that receive most flow. Eventually, all (or at least a desired quantity) of the perforations can be plugged by the plugging devices. However, it can be beneficial to leave some perforations open (as in the example of  FIG. 10 , for pumping well tools to desired locations in the well), and it is not necessary to plug the last open perforations in the method  200 . 
     After releasing plugging devices in step  210 , flow is still monitored in step  204  (for example, to determine when and if the released plugging devices shut off flow through open perforations). Steps  204 ,  206 ,  208 ,  210  can be repeated as many times as desired, until in step  206  a determination is made that all of the perforations intended to be plugged are successfully plugged. 
     Thus, in the  FIG. 11A  example, a zone corresponding to the perforations that initially receive the most flow will be treated (e.g., fractured and/or acidized) first, those perforations will then be plugged, and the next zone corresponding to perforations receiving the most flow will then be treated, and so on, until all of the zones have been treated. Use of the plugging devices results in the zones being progressively treated by diverting flow from treated zones to untreated zones, until all zones have been treated. 
     Additional steps not shown in  FIG. 11A  for the method  200  can be performed. For example, if the plugging devices do not degrade on their own, certain steps can be taken to cause the plugging devices to degrade, or the plugging devices can be dislodged or removed from the perforations to allow fluid to flow from the formation  40  into the wellbore  14 . For example, a fluid can be circulated into the well to cause the plugging devices to degrade, a protective coating on the plugging devices can be abraded or penetrated to allow well fluid to contact and degrade a material of the plugging devices, a well tool can be conveyed into the well to dislodge the plugging devices from the perforations, etc. Thus, the scope of this disclosure is not limited to only the steps depicted in the flowcharts of  FIGS. 11A-E . 
     Referring additionally now to  FIG. 11B , another example of the method  200  is representatively illustrated. In this example, zones with pre-existing perforations are progressively treated in steps  202 - 210  (as described above for the example of  FIG. 11A ) and then, when a determination is made in step  206  that all desired pre-existing perforations have been plugged, new perforations are formed in step  212 . The new perforations may be formed above, below or into the same zones as the pre-existing perforations. 
     The steps  202 - 210  are then performed for the new perforations, so that zones with the new perforations are progressively treated, until in step  206  a determination is made that all of the perforations intended to be plugged are successfully plugged. The plugging devices can degrade or be dislodged from the perforations to allow flow from the formation  40  into the wellbore  14  via the pre-existing and new perforations. 
     Referring additionally now to  FIG. 11C , another example of the method  200  is representatively illustrated. In this example, a plug (such as, a conventional bridge plug or other type of plug) is set in the wellbore above pre-existing perforations in step  214 . Then, new perforations are formed in step  212 . 
     Zones corresponding to the new perforations are then progressively treated in steps  202 - 210 , until in step  206  a determination is made that all of the new perforations intended to be plugged are successfully plugged. The plugging devices can degrade or be dislodged from the new perforations, and the bridge plug can be retrieved or degraded, to allow flow from the formation  40  into the wellbore  14  via the pre-existing and new perforations. 
     Referring additionally now to  FIG. 11D , another example of the method  200  is representatively illustrated. In this example, new perforations are formed at a zone in step  212 , and then steps  202 - 210  are performed as described above for the  FIG. 11A  example, until in step  206  a determination is made that all of the new perforations intended to be plugged are successfully plugged. 
     Then, in step  216  a determination is made whether all intended zones have been completed. If not, then the method returns to step  212 , in which new perforations are formed in the next zone. 
     Steps  202 - 210  are performed for the new perforations, until in step  206  a determination is made that all of the new perforations in a zone intended to be plugged are successfully plugged. Thus, the steps  212  and  202 - 210  are performed for each zone in succession, until all intended zones have been perforated and treated. 
     Referring additionally now to  FIG. 11E , another example of the method  200  is representatively illustrated. In this example, the perforating step  212  is performed below a restriction in the wellbore  14  (such as, the restriction  75  depicted in  FIG. 6A ). The restriction could prevent the use of a conventional plug (such as, a bridge plug) to isolate the perforations, but use of the plugging devices  60  enables the perforations to be plugged below the restriction. 
     After the perforations are formed in step  212 , the steps  202 - 210  are performed to treat the zone penetrated by the perforations. If desired, multiple zones can be treated as in the method  200  example of  FIG. 11D . 
     Referring additionally now to  FIG. 12 , a cross-sectional view of another example of the device  60  is representatively illustrated. The device  60  may be used in any of the systems and methods described herein, or may be used in other systems and methods. 
     In this example, the body of the device  60  is made up of filaments or fibers  62  formed in the shape of a ball or sphere. Of course, other shapes may be used, if desired. 
     The filaments or fibers  62  may make up all, or substantially all, of the device  60 . The fibers  62  may be randomly oriented, or they may be arranged in various orientations as desired. 
     In the  FIG. 12  example, the fibers  62  are retained by the dissolvable, degradable or dispersible material  82 . In addition, a frangible coating (e.g., the frangible coating  88  of the  FIG. 8  example) may be provided on the device  60 , for example, in order to delay dissolving of the material  82  until the device has been deployed into a well (as in the examples of  FIGS. 6A, 6B &amp; 10 ). 
     The device  60  of  FIG. 12  can be used in a diversion fracturing operation (in which perforations receiving the most fluid are plugged to divert fluid flow to other perforations), in a re-completion operation (e.g., as in the  FIGS. 2A-D  example), or in a multiple zone perforate and fracture operation (e.g., as in the  FIGS. 3A-D  example). 
     One advantage of the  FIG. 12  device  60  is that it is capable of sealing on irregularly shaped openings, perforations, leak paths or other passageways. The device  60  can also tend to “stick” or adhere to an opening, for example, due to engagement between the fibers  62  and structure surrounding (and in) the opening. In addition, there is an ability to selectively seal openings. 
     The fibers  62  could, in some examples, comprise wool fibers. The device  60  may be reinforced (e.g., using the material  82  or another material) or may be made entirely of fibrous material with a substantial portion of the fibers  62  randomly oriented. 
     The fibers  62  could, in some examples, comprise metal wool, or crumpled and/or compressed wire. Wool may be retained with wax or other material (such as the material  82 ) to form a ball, sphere, cylinder or other shape. 
     In the  FIG. 12  example, the material  82  can comprise a wax (or eutectic metal or other material) that melts at a selected predetermined temperature. A wax device  60  may be reinforced with fibers  62 , so that the fibers and the wax (material  82 ) act together to block a perforation or other passageway. 
     The selected melting point can be slightly below a static wellbore temperature. The wellbore temperature during fracturing is typically depressed due to relatively low temperature fluids entering wellbore. After fracturing, wellbore temperature will typically increase, thereby melting the wax and releasing the reinforcement fibers  62 . 
     This type of device  60  in the shape of a ball or other shapes may be used to operate downhole tools in a similar fashion. In  FIG. 14 , a well tool  110  is depicted with a passageway  112  extending longitudinally through the well tool. The well tool  110  could, for example, be connected in the casing  16  of  FIG. 1 , or it could be connected in another tubular string (such as a production tubing string, the tubular string  12 , etc.). 
     The device  60  is depicted in  FIG. 14  as being sealingly engaged with a seat  114  formed in a sliding sleeve  116  of the well tool  110 . When the device  60  is so engaged in the well tool  110  (for example, after the well tool is deployed into a well and appropriately positioned), a pressure differential may be produced across the device and the sliding sleeve  116 , in order to shear frangible members  118  and displace the sleeve downward (as viewed in  FIG. 14 ), thereby allowing flow between the passageway  112  and an exterior of the well tool  110  via openings  120  formed through an outer housing  122 . 
     The material  82  of the device  60  can then dissolve, disperse or otherwise degrade to thereby permit flow through the passageway  112 . Of course, other types of well tools (such as, packer setting tools, frac plugs, testing tools, etc.) may be operated or actuated using the device  60  in keeping with the scope of this disclosure. 
     A drag coefficient of the device  60  in any of the examples described herein may be modified appropriately to produce a desired result. For example, in a diversion fracturing operation, it is typically desirable to block perforations in a certain location in a wellbore. The location is usually at the perforations taking the most fluid. 
     Natural fractures in an earth formation penetrated by the wellbore make it so that certain perforations receive a larger portion of fracturing fluids. For these situations and others, the device  60  shape, size, density and other characteristics can be selected, so that the device tends to be conveyed by flow to a certain corresponding section of the wellbore. 
     For example, devices  60  with a larger coefficient of drag (Cd) may tend to seat more toward a toe of a generally horizontal or lateral wellbore. Devices  60  with a smaller Cd may tend to seat more toward a heel of the wellbore. For example, if the wellbore  14  depicted in  FIG. 2B  is horizontal or highly deviated, the heel would be at an upper end of the illustrated wellbore, and the toe would be at the lower end of the illustrated wellbore (e.g., the direction of the fluid flow  44  is from the heel to the toe). 
     Smaller devices  60  with long fibers  62  floating freely (see the example of  FIG. 13 ) may have a strong tendency to seat at or near the heel. A diameter of the device  60  and the free fiber  62  length can be appropriately selected, so that the device is more suited to stopping and sealingly engaging perforations anywhere along the length of the wellbore. 
     Acid treating operations can benefit from use of the device  60  examples described herein. Pumping friction causes hydraulic pressure at the heel to be considerably higher than at the toe. This means that the fluid volume pumped into a formation at the heel will be considerably higher than at the toe. Turbulent fluid flow increases this effect. Gelling additives might reduce an onset of turbulence and decrease the magnitude of the pressure drop along the length of the wellbore. 
     Higher initial pressure at the heel allows zones to be acidized and then plugged starting at the heel, and then progressively down along the wellbore. This mitigates waste of acid from attempting to acidize all of the zones at the same time. 
     The free fibers  62  of the  FIGS. 4-6B &amp; 13  examples greatly increase the ability of the device  60  to engage the first open perforation (or other leak path) it encounters. Thus, the devices  60  with low Cd and long fibers  62  can be used to plug from upper perforations to lower perforations, while turbulent acid with high frictional pressure drop is used so that the acid treats the unplugged perforations nearest the top of the wellbore with acid first. 
     In examples of the device  60  where a wax material (such as the material  82 ) is used, the fibers  62  (including the body  64 , lines  66 , knots, etc.) may be treated with a treatment fluid that repels wax (e.g., during a molding process). This may be useful for releasing the wax from the fibrous material after fracturing or otherwise compromising the retainer  80  and/or a frangible coating  88  thereon. 
     Suitable release agents are water-wetting surfactants (e.g., alkyl ether sulfates, high hydrophilic-lipophilic balance (HLB) nonionic surfactants, betaines, alkyarylsulfonates, alkyldiphenyl ether sulfonates, alkyl sulfates). The release fluid may also comprise a binder to maintain the knot or body  64  in a shape suitable for molding. One example of a binder is a polyvinyl acetate emulsion. 
     Broken-up or fractured devices  60  can have lower Cd. Broken-up or fractured devices  60  can have smaller cross-sections and can pass through the annulus  30  between tubing  20  and casing  16  more readily. 
     A restriction may be connected in any line or pipe that the devices  60  are pumped through, in order to cause the devices to fracture as they pass through the restriction. This may be used to break up and separate devices  60  into wax and non-wax parts. The restriction may also be used for rupturing a frangible coating (e.g., the coating  88  of the  FIG. 8  example) covering a soluble wax material  82  to allow water or other well fluids to dissolve the wax. 
     Fibers  62  may extend outwardly from the device  60 , whether or not the body  64  or other main structure of the device also comprises fibers. For example, a ball (or other shape) made of any material could have fibers  62  attached to and extending outwardly therefrom. Such a device  60  will be better able to find and cling to openings, holes, perforations or other leak paths near the heel of the wellbore, as compared to the ball (or other shape) without the fibers  62 . 
     For any of the device  60  examples described herein, the fibers  62  may not dissolve, disperse or otherwise degrade in the well. In such situations, the devices  60  (or at least the fibers  62 ) may be removed from the well by swabbing, scraping, circulating, milling or other mechanical methods. 
     In situations where it is desired for the fibers  62  to dissolve, disperse or otherwise degrade in the well, nylon is a suitable acid soluble material for the fibers. Nylon 6 and nylon 66 are acid soluble and suitable for use in the device  60 . At relatively low well temperatures, nylon 6 may be preferred over nylon 66, because nylon 6 dissolves faster or more readily. 
     Self-degrading fiber devices  60  can be prepared from poly-lactic acid (PLA), poly-glycolic acid (PGA), or a combination of PLA and PGA fibers  62 . Such fibers  62  may be used in any of the device  60  examples described herein. 
     Fibers  62  can be continuous monofilament or multifilament, or chopped fiber. Chopped fibers  62  can be carded and twisted into yarn that can be used to prepare fibrous flow conveyed devices  60 . 
     The PLA and/or PGA fibers  62  may be coated with a protective material, such as calcium stearate, to slow its reaction with water and thereby delay degradation of the device  60 . Different combinations of PLA and PGA materials may be used to achieve corresponding different degradation times or other characteristics. 
     PLA resin can be spun into fiber of 1-15 denier, for example. Smaller diameter fibers  62  will degrade faster. Fiber denier of less than 5 may be most desirable. PLA resin is commercially available with a range of melting points (e.g., 140 to 365° F.). Fibers  62  spun from lower melting point PLA resin can degrade faster. 
     PLA bi-component fiber has a core of high-melting point PLA resin and a sheath of low-melting point PLA resin (e.g., 140° F. melting point sheath on a 265° F. melting point core). The low-melting point resin can hydrolyze more rapidly and generate acid that will accelerate degradation of the high-melting point core. This may enable the preparation of a fibrous device  60  that will have higher strength in a wellbore environment, yet still degrade in a reasonable time. In various examples, a melting point of the resin can decrease in a radially outward direction in the fiber. 
     It may now be fully appreciated that the above disclosure provides significant advancements to the art of controlling flow in subterranean wells. In some examples described above, the device  60  may be used to block flow through openings in a well, with the device being uniquely configured so that its conveyance with the flow is enhanced. 
     The above disclosure provides to the art a method  200  for use with a subterranean well. In one example, the method  200  can comprise releasing flow conveyed plugging devices  60  into the well, each of the plugging devices  60  including a body  64  and, extending outwardly from the body, at least one of lines  66  and fibers  62 , and the plugging devices  60  blocking flow through respective openings  68  in the well. 
     The method  200  can include flowing a treatment fluid into a first zone  40   a  via the openings  68 . The releasing step may be performed with or after the treatment fluid flowing step. The method  200  may include perforating the first zone  40   a  prior to the treatment fluid flowing step. 
     The treatment fluid may be a stimulation fluid (such as, a fracturing and/or acidizing fluid), an inhibitor or a damage remediation fluid. Multiple treatment fluids and various combinations of treatment fluids may also be used in keeping with the scope of this disclosure. 
     The method  200  may include perforating a second zone  40   b  after the blocking step. The method  200  may include performing the releasing and treatment fluid flowing steps for the second zone  40   b.    
     The method  200  may include setting a plug in the well prior to the releasing step. The method  200  may include perforating a second zone  40   b  after the setting step. 
     The lines  66  and/or fibers  62  may have a lateral dimension substantially less than a size of the body  64 . 
     The blocking step may comprise the body  64  of each plugging device  60  sealingly engaging the respective opening  68 . The blocking step may comprise the lines  66  and/or fibers  62  entering the respective openings  68 . 
     The body  64  of each of the plugging devices  60  may comprise a knot. 
     Each of the plugging devices  60  may comprise a degradable material. The degradable material may be selected from the group consisting of poly-vinyl alcohol, poly-vinyl acetate, poly-methacrylic acid, poly-lactic acid and poly-glycolic acid. 
     The lines  66  and/or fibers  62  may comprise a film, tube, filament, fabric and/or sheet material. 
     The plugging devices  60  may be conveyed by flow through a restriction  75  in the well. 
     Another example of a method  200  for use with a subterranean well is provided to the art by the above disclosure. In this example, the method  200  can comprise perforating a first zone  40   a , releasing a first set of flow conveyed plugging devices  60  into the well, each of the plugging devices  60  including a body  64 , and lines  66  and/or fibers extending outwardly from the body, the first set of plugging devices  60  blocking flow through respective perforations  46   a  in the first zone  40   a , perforating a second zone  40   b , releasing a second set of the flow conveyed plugging devices  60  into the well, and the second set of plugging devices  60  blocking flow through respective perforations  46   b  in the second zone  40   b.    
     The method may include flowing a treatment fluid into the first zone  40   a . The step of releasing the first set of plugging devices  60  may be performed with or after the treatment fluid flowing step. 
     The step of perforating the second zone  40   b  may be performed after the step of blocking flow through the perforations  46   a  in the first zone  40   a . The method  200  may include flowing the treatment fluid into the second zone  40   b  after the step of perforating the second zone  40   b.    
     Although various examples have been described above, with each example having certain features, it should be understood that it is not necessary for a particular feature of one example to be used exclusively with that example. Instead, any of the features described above and/or depicted in the drawings can be combined with any of the examples, in addition to or in substitution for any of the other features of those examples. One example&#39;s features are not mutually exclusive to another example&#39;s features. Instead, the scope of this disclosure encompasses any combination of any of the features. 
     Although each example described above includes a certain combination of features, it should be understood that it is not necessary for all features of an example to be used. Instead, any of the features described above can be used, without any other particular feature or features also being used. 
     It should be understood that the various embodiments described herein may be utilized in various orientations, such as inclined, inverted, horizontal, vertical, etc., and in various configurations, without departing from the principles of this disclosure. The embodiments are described merely as examples of useful applications of the principles of the disclosure, which is not limited to any specific details of these embodiments. 
     In the above description of the representative examples, directional terms (such as “above,” “below,” “upper,” “lower,” etc.) are used for convenience in referring to the accompanying drawings. However, it should be clearly understood that the scope of this disclosure is not limited to any particular directions described herein. 
     The terms “including,” “includes,” “comprising,” “comprises,” and similar terms are used in a non-limiting sense in this specification. For example, if a system, method, apparatus, device, etc., is described as “including” a certain feature or element, the system, method, apparatus, device, etc., can include that feature or element, and can also include other features or elements. Similarly, the term “comprises” is considered to mean “comprises, but is not limited to.” 
     Of course, a person skilled in the art would, upon a careful consideration of the above description of representative embodiments of the disclosure, readily appreciate that many modifications, additions, substitutions, deletions, and other changes may be made to the specific embodiments, and such changes are contemplated by the principles of this disclosure. For example, structures disclosed as being separately formed can, in other examples, be integrally formed and vice versa. Accordingly, the foregoing detailed description is to be clearly understood as being given by way of illustration and example only, the spirit and scope of the invention being limited solely by the appended claims and their equivalents.