Patent Publication Number: US-2022228456-A1

Title: Discrete plugging device launcher

Description:
TECHNICAL FIELD 
     This disclosure relates generally to equipment utilized and operations performed in conjunction with a subterranean well and, in examples described below, more particularly provides a discrete plugging device launcher. 
     BACKGROUND 
     Plugging devices can be used to plug perforations in subterranean wells. Typically, plugging devices are deployed as a group into a well, with the number of plugging devices being equal to, or greater than, the number of perforations, so that all perforations are plugged. 
     However, it can be difficult to ensure that every plugging device will plug a respective perforation. For example, if two plugging devices are displacing toward a last, deepest perforation, only one of the plugging devices will typically be able to plug the perforation. 
     It will, therefore, be readily appreciated that improvements are continually needed in the art of deploying plugging devices into subterranean wells. It is among the objects of the present disclosure to provide such improvements to the art. 
    
    
     
       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. 
         FIG. 2  is a representative perspective and partially cross-sectional view of an example of a release mechanism of a plugging device launcher that may be used in the  FIG. 1  system and method, and that can embody the principles of this disclosure. 
         FIG. 3  is a representative end view of the release mechanism. 
         FIG. 4  is a representative perspective and partially cross-sectional view of another example of the release mechanism. 
         FIG. 5  is a representative perspective and partially cross-sectional view of another example of the release mechanism. 
         FIG. 6  is a representative perspective and partially cross-sectional view of another example of the release mechanism. 
         FIG. 7  is a representative cross-sectional view of an example of the plugging device launcher configured for positioning downhole in a well. 
         FIG. 8  is a representative perspective side view of an example of the plugging device launcher configured for positioning at a surface location. 
         FIG. 9  is a representative cross-sectional view of the  FIG. 8  plugging device launcher. 
         FIG. 10  is a representative perspective and cross-sectional view of the plugging device launcher, depicting a reel and level guide section of the release mechanism. 
         FIG. 11  is a representative perspective and cross-sectional view of the plugging device launcher, depicting a pawl mechanism and shaft section of the release mechanism. 
         FIG. 12  is a representative detailed perspective view of the pawl mechanism. 
         FIG. 13  is a representative detailed perspective view of the reel and level guide section of the release mechanism. 
     
    
    
     DETAILED DESCRIPTION 
     Representatively illustrated in  FIG. 1  is a system  10  for use with a subterranean 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 wellbore  12  has been drilled into an earth formation  14 . The wellbore  12  is lined with casing  16 . Perforations  18  are formed through the casing  16  (and any surrounding cement) and into the formation  14  to thereby provide fluid communication between the wellbore  12  and the formation  14 . 
     Although the perforations  18  are depicted in  FIG. 1  as being formed in a generally horizontal section of the wellbore  12 , in other examples the perforations could be formed in a generally vertical or inclined section of the wellbore. The perforations  18  may be divided into separate groups, sets or clusters as depicted in  FIG. 1 , or the perforations may be in a single group, set or cluster. Instead of the casing  16 , a liner, tubing, pipe or other type of tubular may form a protective lining for the wellbore  12 . Thus, the scope of this disclosure is not limited to any particular details of the system  10  as representatively illustrated in  FIG. 1 . 
     It is desired in the  FIG. 1  example to plug off some or all of the perforations  18 . For example, in a treatment or stimulation operation (such as, a fracturing, acidizing, conformance or permeability modifying operation), it can be beneficial to plug off perforations  18  that initially receive most of an injected fluid  20  flow, so that other zones or portions of the formation  14  can receive a desired volume of the injected fluid. The injected fluid  20  may be any type of treatment fluid (such as, water, brine, acid, gel, breaker, conformance agent, permeability modifier, etc.) or any other fluid suitable for injection into the wellbore  12  or formation  14 . 
     Plugging devices  22  are conveyed with the flow of the fluid  20  to the perforations  18  in this example. When one of the plugging devices  22  engages or seats on a perforation  18 , flow of the fluid  20  into the formation  14  via that perforation is blocked by the plugging device. Suitable plugging devices for use in the system  10  are described in US publication no.  2017 / 0260828 , the entire disclosure of which is incorporated herein by this reference. However, the scope of this disclosure is not limited to use of any particular type or configuration of the plugging devices. 
     To assist with deployment of the plugging devices  22  into the wellbore  12 , the system  10  includes a discrete plugging device launcher  24 . The plugging device launcher  24  includes a controllable release mechanism  26  that releases one or more plugging device(s)  22  at a controlled rate into the flow of the fluid  20 . 
     As depicted in  FIG. 1 , the plugging device launcher  24  is connected between a pump  27  and a wellhead  29 . The pump  27  pumps the fluid  20  through the plugging device launcher  24  and into the wellhead  29 . When it is desired to release one or more plugging device  22  into the fluid  20  flow, the release mechanism  26  is appropriately actuated, as described more fully below. 
     Representatively illustrated in  FIGS. 2-13  are examples of the plugging device launcher  24  and release mechanism  26  thereof, and associated methods, which can embody principles of this disclosure. However, it should be clearly understood that these are merely examples of applications 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 plugging device launcher  24 , release mechanism  26  and method examples described herein and/or depicted in the drawings. 
     Plugging devices are sometimes used to completely plug a group of perforations in a well. A common reason to plug up every perforation is for plug replacement. The number of perforations may range from as few as 1 to more than 100. 
     When deployed into a well with fluid flow, plugging devices can have three fluid forces acting on them that affect where an individual plugging device will land in a group of open perforations. A first force is fluid drag that is pushing the plugging device down hole with fluid flow. A second force is fluid drag that pushes a plugging device radially toward a perforation with fluid flow into the perforation, as the plugging device approaches the location of the perforation. The radial distance, relative to the casing, from the perforation to the plugging device has a strong effect on fluid drag pulling a plugging device to the perforation. A third force is a holding force on a perforation when the downhole fluid drag is still pulling it. Perforation size, perforation location, and the amount of fluid a perforation is taking all affect the location where a plugging device will land (engage and block flow through an opening such as a perforation). 
     The last (deepest, farthest downhole) open perforation has a downhole drag force of zero and generally will not be passed up by a plugging device on a horizontal well. The gravitational effect acting on a plugging device in a vertical well is very small and should typically be smaller than the force pulling the plugging device to the last open perforation. Typically, the last perforation is readily plugged with a plugging device. 
     It has been found in testing that if a single plugging device is pumped through a group of open perforations, the plugging device will tend to land approximately in a center of the group of perforations. If a group of plugging devices are released and pumped close together, they will also tend to start seating at about a half way point of the group of perforations. Plugging devices do not move uphole because there is no fluid movement in that direction. 
     Plugging devices are preferably generously spaced apart during release, so that the upper (shallowest, farthest uphole) perforations, as each of them eventually become the last (deepest) open perforation, will each have a plugging device at or above it as this occurs. 
     The plugging device launcher is preferably able to release plugging devices slowly, in order to space them out enough to accomplish a complete plugging of every perforation. If the plugging devices are released too slow, displacement water or treatment fluid and time are wasted (each of them being costly). A nominal desired spacing between plugging devices is the time it takes for a plugging device to travel a distance from the very top (shallowest) perforation to the very last (deepest) perforation. In practice, the spacing is generally less than this to save time and fluid. 
     Since the length and number of perforations varies greatly from well to well, it is desirable to have a release mechanism that is easily adjusted to space out plugging devices to a minimum amount, without too much excess. There are occasions when it is desirable to release plugging devices in a large, tight group. 
     In examples described herein, plugging devices can be released via a downhole wireline conveyed device and through a surface plugging device launcher. In some examples, both may be used together. 
     A basic mechanism for releasably securing plugging devices described herein is a pin that penetrates the plugging device through an opening (such as, a loop in threads or fibers of the plugging devices, a rigid loop of the plugging device, a piece of tape with a hole in it or a drilled hole in the plugging device). The plugging device is released by retracting the pin from the opening. 
     The pin may be a wire, a string, a rod, a paper or plastic clip, or any type of elongated device. The pin may be long such that, as the pin is retracted, plugging devices are released in sequence. The pin may be retracted continuously or in discrete movements to control a rate at which plugging devices are released. The pin may be removed axially, radially, tangentially, or a combination of these. 
     Referring additionally now to  FIGS. 2 &amp; 3 , an example of the release mechanism  26  is representatively illustrated, apart from the remainder of the system  10  and the plugging device launcher  24 . The  FIGS. 2 &amp; 3  release mechanism  26  (as well as other examples of the release mechanism described herein) may be used with the system  10 , plugging device launcher  24  and method of  FIG. 1 , or it may be used with other systems, plugging device launchers and methods. 
     In the  FIGS. 2 &amp; 3  example, each of multiple plugging devices  22  is retained by a circumferentially extending elongated member  28  (such as a wire or pin) attached to a rotatable rod or shaft  30 . An individual circular member  28  may extend more than once about the shaft  30  to allow for more than 360° of rotation prior to release of the corresponding plugging device  22 . 
     Each member  28  is received in an opening  32  (for example, a hole, loop, etc.), of the plugging device  22  that is inserted through a wall of a tube  34 . In this example, the opening  32  is formed by a loop of wire extending outward from the plugging device  22 . 
     While the member  28  remains in the opening  32 , the corresponding plugging device  22  is retained adjacent the tube  34 . When the shaft  30  is rotated, the plugging devices  22  are sequentially released from the respective members  28  for deployment into a well. 
     As depicted in  FIGS. 2 &amp; 3 , the members  28  have different circumferential lengths. Thus, a respective one of the plugging devices  22  will first be released from the shortest member  28 , a respective one of the plugging devices will then be released from the next shortest member, etc., as the shaft  30  is rotated. 
     In other examples, multiple members  28  could have the same length, so that multiple plugging devices  22  are released at the same time. Alternatively, multiple plugging devices  22  can be released at the same time by retaining the multiple plugging devices on a same member  28 . 
     Note that a speed of rotation of the shaft  30  is proportional to a rate of release of the plugging devices  22  from the release mechanism  26 . Faster rotation of the shaft  30  will result in an increased rate of release of the plugging devices  22 , and slower rotation of the shaft will result in a decreased rate of release of the plugging devices. 
     Referring additionally now to  FIG. 4 , another example of the release mechanism  26  is representatively illustrated. In this example, the shaft  30  is displaced axially or longitudinally, instead of rotated, in order to release the plugging devices  22 . 
     As depicted in  FIG. 4 , multiple plugging devices  22  are retained by multiple elongated members  28  secured to the shaft  30 . The members  28  are received in the openings  32  of the plugging devices  22  that are extended through a wall of the tube  34 . Note that the members  28  in this example extend longitudinally, instead of circumferentially (as in the  FIGS. 2 &amp; 3  example). 
     While a member  28  remains in an opening  32 , the corresponding plugging device  22  is retained adjacent the tube  34 . When the shaft  30  is displaced axially or longitudinally, the plugging devices  22  are sequentially released from the respective members  28  for deployment into a well. 
     As depicted in  FIGS. 4 , the members  28  have different lengths. Thus, a respective one of the plugging devices  22  will first be released from the shortest member  28 , a respective one of the plugging devices will then be released from the next shortest member, etc., as the shaft  30  is displaced. 
     In other examples, multiple members  28  could have the same length, so that multiple plugging devices  22  are released at the same time. Alternatively, multiple plugging devices  22  can be released at the same time by retaining the multiple plugging devices on a same member  28 . 
     Note that a speed of displacement of the shaft  30  is proportional to a rate of release of the plugging devices  22  from the release mechanism  26 . Faster displacement of the shaft  30  will result in an increased rate of release of the plugging devices  22 , and slower displacement of the shaft will result in a decreased rate of release of the plugging devices. 
     Referring additionally to  FIG. 5 , another example of the release mechanism  26  is representatively illustrated. In this example, the member  28  is in the form of a helically extending coil (such as, a wire coil or spring). Each plugging device  22  includes an outwardly extending object  36  positioned between adjacent coils of the member  28 . 
     In the  FIG. 5  example, the object  36  is in the form of a knob or ball extending through a slot  38  in the tube  34  and between coils of the member  28 . The object  36  could be anything that is too big to pass through the slot  38  (such as a knot tied in a string). 
     An opening (such as the opening  32  in the  FIGS. 2-4  examples) could be used in place of the object  36 . For example, the member  28  of  FIG. 5  could be received in a loop of string, fiber, plastic, metal, etc. extending outward from each of the plugging devices  22 . 
     As the member  28  is rotated in the  FIG. 5  example, the plugging devices  22  are advanced along the tube  34  between the coils. At an end of the tube  34  (or at a location where the slot  38  is enlarged so that the object  36  can pass through the slot), each plugging device  22  is eventually released into the well. 
     Note that a speed of rotation of the shaft  30  and member  28  is proportional to a rate of release of the plugging devices  22  from the release mechanism  26 . Faster rotation of the shaft  30  will result in an increased rate of release of the plugging devices  22 , and slower rotation of the shaft will result in a decreased rate of release of the plugging devices. 
     Referring additionally now to  FIG. 6 , another example of the release mechanism  26  is representatively illustrated. In this example, the member  28  is in the form of a flexible wire or cable extending through the openings  32  of the plugging devices  22 . 
     Each plugging device  22  is retained adjacent the tube  34  as long as the member  28  extends through the opening  32  of the plugging device. However, when the member  28  is retracted, so that it no longer extends through the opening  32 , the corresponding plugging device  22  is released for deployment into the well. 
     When the member  28  is displaced axially or longitudinally, the plugging devices  22  are sequentially released. In other examples, multiple plugging devices  22  can be released at the same time by retaining the multiple plugging devices at a same location along the member  28 . 
     Note that a speed of displacement of the member  28  is proportional to a rate of release of the plugging devices  22  from the release mechanism  26 . Faster displacement of the member  28  will result in an increased rate of release of the plugging devices  22 , and slower displacement of the member will result in a decreased rate of release of the plugging devices. 
     Referring additionally now to  FIG. 7 , an example of a downhole plugging device launcher  40  is representatively illustrated. The  FIG. 7  plugging device launcher  40  may be used with the plugging device launcher  24  described above, or it may be used separately. 
     In this example, the plugging device launcher  40  is configured to be conveyed into a well (such as, into the wellbore  12  in the  FIG. 1  system  10 ). The plugging device launcher  40  may be conveyed by wireline, slickline, coiled tubing or another type of conveyance. 
     As depicted in  FIG. 7 , the plugging device launcher  40  includes an upper electrical connector  42  (e.g., for connection to an electrical conductor of a wireline), an oil-filled chamber  44 , an electrical motor  46  or other type of actuator, a drum, spool or reel  48  driven by the motor or actuator, and the release mechanism  26  of  FIG. 6 . Only the tube  34  of the release mechanism  26  is visible in  FIG. 7  (e.g., after the elongated member  28  has been retracted out of engagement with the openings  32 , and after the plugging devices  26  have all been released). Note that any of the release mechanism  26  examples described herein may be used in the plugging device launcher  40 . 
     When the motor  46  is operated, the member  28  is wound about the reel  48 , thereby withdrawing the member from the openings  32 . Flow of the fluid  20  through a slotted outer housing  50  of the plugging device launcher  40  carries the plugging devices  26  downhole. 
     In an inclined wellbore, preferably a slot in the outer housing  50  faces upward. An eccentric pump-down bushing  52  and/or a cantilever spring may be used to orient the slot upward. 
     The motor  46  speed and duration can be controlled by a control system of a wireline truck or operations cab. Thus, a rate of release of the plugging devices  26  can be varied by varying a speed of the motor  46 . Other actuators or means to withdraw or retract the member include displacement of a packer setting tool, retraction of a spring, use of a piston and ambient chamber, etc. 
     One advantage of the plugging device launcher  40  is that excess plugging devices  26  can be run into the well. When all the perforations  18  are plugged and the well pressures up (e.g., pressure in the wellbore  12  increases due to the lack of a flow path to the formation  14 ), the motor  46  can be turned off to thereby cease further plugging device  26  release. Excess plugging devices  26  can then be retrieved from the well with the plugging device launcher  40 . 
     Referring additionally now to  FIGS. 8-13 , various views of an example of the plugging device launcher  24  are representatively illustrated. The plugging device launcher  24  may be used in the system  10  and method of  FIG. 1 , or it may be used with other systems and methods. 
     The  FIGS. 8-13  plugging device launcher  24  utilizes the  FIG. 6  release mechanism  26 . However, in other examples, other types of release mechanisms may be used. 
     The actuator for the  FIGS. 8-13  plugging device launcher  24  is a rotary hydraulic actuator  54  combined with a pawl mechanism  56 . For convenience, the reel  48  on which the member  28  is wound is sized so that only one plugging device  22  is released per stroke of the hydraulic actuator  54  in the  FIGS. 8-13  example. A hydraulic or electric motor could be used in place of the rotary hydraulic actuator  54 . 
       FIG. 8  depicts an outside of the plugging device launcher  24 . A position indicator flag  58  is used to indicate to an operator that a shaft  60  (see  FIG. 11 ) that transmits rotation from the actuator  54  to the reel  48  is rotating properly. 
     Fluid  20  flowing into the well is directed to a treatment line inlet  62  (connected to the pump  27  in the  FIG. 1  system  10 ). The rotary hydraulic actuator  54  is operated to release the plugging devices  22  into a treatment line outlet  64  (connected to the wellhead  29  in the  FIG. 1  system  10 ). From the treatment line outlet  64 , the released plugging devices  22  enter the well, are conveyed by the fluid  20  flow through the well and eventually land on and block flow through a perforation  18  or other opening. 
     In  FIG. 9 , a cross section of the plugging device launcher  24  is representatively illustrated. There are two flow restrictors  66 ,  68  positioned in respective flow lines  70 ,  72 . The restrictor  66  in the flow line  70  is used to divert some flow of the fluid  20  through the flow line  72  leading to the release mechanism  26 . This restrictor  66  is not strictly necessary, because the fluid  20  should readily flow through the flow line  72 . 
     The restrictor  68  in the flow line  72  is used to limit a flow rate of the fluid  20  around the plugging devices  22 , in order to prevent damage to the plugging devices. The restrictor  68  is also not necessary in all examples. 
     A plug  74  is visible in  FIG. 9 . The plug  74  prevents the plugging devices  22  from getting caught in a dead space near a reload access valve  76 . The reload access valve  76  is used to access the release mechanism  26  when it is desired to load additional plugging devices  22  or otherwise maintain or reset the release mechanism. 
     In  FIG. 10 , a more detailed view of the reel  48  and a level guide  78  is representatively illustrated. The reel  48  has a pawl  80  on it to prevent entanglement of the member  28  during installation of the release mechanism  26 . 
     In operation, the level guide  78  rotates due to friction against the member  28  as it is wound onto the reel  48 . The level guide  78  rotates on a threaded shaft  82  that will laterally advance the member  28  at an appropriate rate to prevent the member from stacking onto itself on the reel  48 . The purpose of this is to keep the feed rate (displacement speed) of the member  28  constant. 
     In  FIG. 11 , a cross-sectional view of the plugging device launcher  24  is representatively illustrated. In this view, the manner in which the reel  48  is rotated via the pawl mechanism  56  can be seen. 
     In  FIG. 12 , a more detailed view of the pawl mechanism  56  is representatively illustrated. In this view, the manner in which rotation of the shaft  60  is controlled by the pawl mechanism  56  can be seen. 
     In  FIG. 13 , a more detailed view of the reel  48  and level guide  78  is representatively illustrated. In this view, the manner in which the level guide  78  controls winding of the member  28  onto the reel  48  can be seen. 
     The plugging device launcher  24  described herein allows precise release of plugging devices  22 , thereby providing for accurate spacing of the plugging devices. Another advantage is that more than one release of plugging devices  22  may be accomplished. Multiple launchers  24  can be utilized (for example, connected in parallel) when more than one release of plugging devices  22  per treatment stage is desired. 
     In the case of the downhole plugging device launcher  40  described above, extremely slow release of plugging devices  22  may be accomplished without danger of releasing extra plugging devices above new perforations  18 . 
     It may now be appreciated that the above disclosure provides to the art a plugging device launcher  24 ,  40  for use with a subterranean well. In one example, the plugging device launcher  24 ,  40  can include: a release mechanism  26  comprising an actuator  46 ,  54  operative to displace at least one elongated member  28 . The at least one elongated member  28  is engaged with at least one plugging device  22 . 
     In any of the examples described above: 
     The plugging device launcher  24  can include a flow line  70  configured to connect between a pump  27  and a wellhead  29  of the well. 
     The plugging device launcher  40  may include an outer housing  50  containing the release mechanism  26 . The outer housing  50  may be configured to be positioned downhole in the well. 
     The “at least one” elongated member  28  may be a single elongated member, the “at least one” plugging device may comprise multiple plugging devices, and the single elongated member  28  may be engaged with each of the multiple plugging devices  22 . The single elongated member  28  may be received in an opening  32  of each of the multiple plugging devices  22 . 
     The “at least one” elongated member  28  may comprise multiple elongated members, the “at least one” plugging device  22  may comprise multiple plugging devices, and each of the elongated members  28  may be engaged with a respective one of the multiple plugging devices  22 . Each of the elongated members  28  may be received in an opening  32  of the respective one of the multiple plugging devices  22 . 
     The actuator  46 ,  54  may be configured to longitudinally displace or rotate the elongated member  28 . The actuator  46 ,  54  may be configured to wind the elongated member  28  onto a reel  48 . 
     A method of releasing plugging devices  22  into a subterranean well is also provided to the art by the above disclosure. In one example, the method can include placing a plugging device launcher  24 ,  40  in communication with a wellbore  12  of the well; and operating an actuator  46 ,  54  of the plugging device launcher  24 ,  40 , thereby displacing at least one elongated member  28  of the plugging device launcher  24 ,  40 . The displacing step can include disengaging the at least one elongated member  28  from at least one of the plugging devices  22 . 
     In any of the examples described above: 
     The “at least one” elongated member  28  may be a single elongated member, and the disengaging step may include disengaging the single elongated member  28  from the plugging devices  22 . The disengaging step may further include withdrawing the single elongated member  28  from an opening  32  of each of the plugging devices  22 . The disengaging step may include sequentially disengaging the single elongated member  28  from the plugging devices  22 . 
     The “at least one” elongated member  28  may comprise multiple elongated members, and the disengaging step may include disengaging each of the elongated members  28  from a respective one of the plugging devices  22 . The disengaging step may further include withdrawing each of the elongated members  28  from an opening  32  of the respective one of the plugging devices  22 . The disengaging step may include sequentially disengaging each of the elongated members  28  from a respective one of the plugging devices  22 . 
     The displacing step may include longitudinally displacing or rotating the “at least one” elongated member  28 . The displacing step may include winding the “at least one” elongated member  28  onto a reel  48 . 
     The placing step may include connecting the plugging device launcher  24  between a pump  27  and a wellhead  29  of the well. The placing may include positioning the plugging device launcher  40  in the wellbore  12 . 
     The above disclosure provides to the art a plugging device launcher  24 ,  40 , in which member  28  (such as, a wire, pin, helical spring or rod) is disengaged from a plugging device  22  in order to release the plugging device  22 . Multiple wires, springs, pins or rods may be disengaged from respective multiple plugging devices  22 . A single member  28  (e.g., wire, spring, pin or rod) may be disengaged from multiple plugging devices  22 . 
     The plugging device  22  may be released through a wall of a tube  34  in which the member  28  is received. A loop, opening  32 , hole or other receiver of the plugging device  22  may extend through the wall of the tube  34 . 
     The member  28  may be displaced axially or rotated to release the plugging device  22 . Multiple plugging devices  22  may be released sequentially (e.g., in order, one after another) from the launcher  24 ,  40  into a well. A timing between releases of the plugging devices  22  may be selected to provide for each released plugging device  22  landing on a respective perforation  18  or other opening to thereby block flow through the perforation or other opening. 
     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.