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TECHNICAL FIELD 
       [0001]    The present disclosure relates generally to plugs for downhole cementing and other completion operations, and, more particularly, to a plug capable of performing multiple functions downhole. 
       BACKGROUND 
       [0002]    Hydrocarbons, such as oil and gas, are commonly obtained from subterranean formations that may be located onshore or offshore. The development of subterranean operations and the processes involved in removing hydrocarbons from a subterranean formation typically include a number of different steps such as, for example, drilling a wellbore at a desired well site, treating the wellbore to optimize production of hydrocarbons, and performing the necessary steps to produce and process the hydrocarbons from the subterranean formation. 
         [0003]    The steps of completing the well, including well stimulation, well enhancement, zonal isolation, sand control, and other completion steps often use tubular downhole tools to perform a variety of functions. These downhole tools are often operated with a ball or plug. The plug or ball lands and seals on a sleeve or seat internal to the tool, allowing pressure to be generated. The pressure build up enables the sleeve or seat to slide from one position to another position. The sleeve or seat can thus move from a closed position to an open position, whereby casing ports are opened, thus allowing fluids to flow into the annulus or subterranean formation. Downhole plugs are a fairly simple and generally reliable means of activating downhole tools. 
         [0004]    One of the drawbacks of downhole plugs, however, is that after a particular downhole operation has been performed, the plug needs to be moved out of the way to continue operations. One technique for doing this involves drilling the plug out of the downhole tool. Another technique involves pumping fluid downhole at such a high pressure that the plug is forced down and sometimes out of the downhole tool. 
         [0005]    Recent develops have led to efforts to optimize the use of the downhole plugs, for example, by reusing them in subsequent wellbore operations. Such efforts include designing the seats that the plugs set into to shear at high pressures. This enables the plugs to travel downhole for subsequent use. This solution, however, is less than optimal because there are a number of restrictions within the casing, including the inner diameter of the casing itself and coupling transitions, which can interfere with the dislodged seats. 
         [0006]    The present disclosure is directed to a multi-function plug, which includes a detachable member, which enables the plug to engage with at least two seats to perform at least two separate downhole operations. By employing a detachable member, the plug have a reduced outer diameter, which enables to continue downhole with minimal chance of forming an obstruction. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    For a more complete understanding of the present disclosure and its features and advantages, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which: 
           [0008]      FIG. 1  is an isometric view of a plug in accordance with the present disclosure; 
           [0009]      FIG. 2  is an isometric view of the plug shown in  FIG. 1  illustrating separation of a shear ring from the body of the plug (with the pins shown intact for clarity); 
           [0010]      FIG. 3  is cross-sectional view of the plug shown in  FIG. 1 ; 
           [0011]      FIG. 4  is a partial cut-away view of an upper tool seated with the plug shown in  FIG. 1  taken along a longitudinal plane; 
           [0012]      FIG. 5  is a partial cut-away view of the upper tool shown in  FIG. 4  illustrating the plug shifting the tool from a closed position to an open position; 
           [0013]      FIG. 6  is a partial cut-away view of the upper tool of  FIG. 4  shown in the open position with only the shear ring of the plug remaining in the seat; and 
           [0014]      FIG. 7  is a partial cut-away view showing the plug seated in a lower tool. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    Illustrative embodiments of the present disclosure are described in detail herein. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation specific decisions must be made to achieve developers&#39; specific goals, such as compliance with system related and business related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of the present disclosure. Furthermore, in no way should the following examples be read to limit, or define, the scope of the disclosure. 
         [0016]    A multi-function downhole plug  10  in accordance with the present disclosure is shown in  FIG. 1 . The plug  10  is defined by a main body portion  12 , which is generally tubular shaped. The main body portion  12  of the plug has a center bore section  14  which is hollow along approximately ⅔rds of the length of the main body  12 , as shown in  FIG. 3 . The hollow section opens at the tip or nose of the plug  16 . A cap  18  is placed at the tip or nose  16  of the plug  10 . 
         [0017]    The cap  18  covers the open end of the main body  12  and prevents fluids and other downhole elements from entering into the hollow portion of the plug  10 . The cap  18  may be formed of an elastomeric or other suitable material known to those of ordinary skill in the art. The main body  12  may be formed of any suitable material which can withstand the harsh downhole environment, such as, for example, a metal alloy or rigid thermoplastic material. 
         [0018]    The plug  10  is further defined by a hub  20 , which is attached to the distal end of the main body  12 , with the tip  16  being at the proximal end as a point of reference. The hub  20  has the shape of some car tire hubs, namely, generally circular with a forward taper, as best illustrated in  FIGS. 1-2 . The forward taper allows the hub  20  to have generally aerodynamic shape in the rear portion of the plug  10  thereby enabling it to move through casing or work string with minimal resistance. The main body  12  of the plug has a slightly smaller diameter at the distal end to enable the hub  20  to be secured over the distal end of the main body, as illustrated in  FIG. 3 . The hub  20  can be secured to the main body  12  using known mounting techniques, including, but not limited to welding, cementing, and the like. The hub  20  may be formed of the same material used to form the main body  12 , but alternatively, may be formed of a different material, for example, a less rigid material. 
         [0019]    The hub  20  has a generally flat section at its distal end which enables a ring  22  to be secured to it. The ring  22  has a greater diameter than the largest diameter portion of the hub  20 , which is at the distal end. The ring  22  is secured to the end of the hub  20  may any one of a variety of known attached means. In one exemplary embodiment, the ring  22  is secured to the distal end of the hub using a plurality of shear pins  24  equally disposed around the circumferential surface of the ring  22  and hub  20 . In the exemplary embodiment illustrated in  FIGS. 1-3 , ten shear pins  24  are illustrated. Those of ordinary skill in the art will understand and be able to determine the optimum number of shear pins to use, and their optimum size and grade, depending upon the particular application that the plug  10  will be used in. The ring  22  may be formed of the same material used to form the hub  20  and/or main body portion  12 . The ring  22  also has a generally cylindrical shape with a forward facing taper, as best illustrated in  FIG. 2 . The forward facing taper is employed to continue the aerodynamic shape of the hub  20  at its distal end where the ring  22  is attached. As will be explained further below, the ring  22  enables the plug  10  to engage itself in at least two different downhole seats, which in turn enables the plug  10  to carry out at least two separate downhole operations. Furthermore, as those of ordinary skill in the art will appreciate, a plurality of nested rings  22  may be utilized with each layer of nested rings shearing off from the previous layer as downhole functions are performed. Thus, more than two downhole operations can be performed if multiple rings  22  are utilized. 
         [0020]    The downhole plug  10  may have other optional features common among downhole plugs. For example, the downhole plug  10  may further include one or more wiper cups  26  and  28  as illustrated in  FIGS. 1-3 . The wiper cups  26  and  28  are known in the art and are used to wipe the inner walls of the casing string as the plug  10  is deployed downhole. In particular, the wiper cups  26  and  28  may be used to wipe the casing ID of mud cake and other debris. They can also be used as a mechanical separator between two separate and distinct types of fluid being pumped downhole, e.g., mud and cement. The wiper cups  26  and  28  have a generally cylindrical shape with a forward facing taper, which like the forward facing taper on the hub  20  and ring  22 , enhance the aerodynamics of the plug  10  has a travels through one or more fluids downhole. The wiper cups  26  and  28  are generally formed of an elastomeric or rubber material, but can be formed of other suitable flexible materials which can withstand downhole conditions as well as have the ability to flex to conform to the non-uniform profile encountered by the plug  10  as it travels downhole. 
         [0021]    An additional optional feature that the plug  10  may include are centralizers.  FIGS. 1-3  shown two centralizers, one secured to the proximal end  30  and another secured to the distal end  32 . As those of ordinary skill in the art, one or more or no centralizers may be employed depending upon the applications. The specific centralizers  30  and  32  that are illustrated, are generally star-shaped and have six equally spaced arms. Again, the number of arms used may be varied. The centralizers  30  and  32  aid in maintaining the plug in a generally centralizer axial position as the travels downhole. This helps to minimize the possibility that the plug  10  may get stuck in an undesirable location. The centralizers  30  and  32  may be formed of a suitable elastomeric or similar material, which can withstand downhole conditions, but also have enough rigidity to allow maintain the plug  10  in a centralized orientation. The proximal centralizer  30  is held in place onto the main body  12  by the elastomeric end cap  18 . It may also be cemented or otherwise bonded to the main body  12  to ensure it does not separate from the main body. Likewise, the end cap  18  may be bonded to the tip  16  of the main body  12 . Similarly, the distal centralizer  32  is held in place onto the distal end of the plug  10  by an elastomeric distal end cap  34 , as best shown in  FIG. 3 . The distal centralizer  32  and end cap  34  may also be bonded to the main body  12  using a cement or other similar bonding agent. 
         [0022]    With reference to  FIGS. 4-7 , the present disclosure will now discuss how the multi-function downhole plug  10  may operate. The plug  10  is deployed downhole through a section of casing string  36  until it reaches a section of the casing string identified as upper tool  38 , shown in  FIG. 4 . The upper tool  38  is a section of the casing string which performs a downhole function, for example, injecting downhole fluid into the wellbore and/or formation through ports  40 . The plug  10  lands in a two part seat  42   a  and  42   b . Seat  42   a  may also be referred to as a closing seat and seat  42   a  may also be referred to as an opening seat  42   b . Seats  42   a  and  42   b  are both secured to the inner circumferential surface of the upper tool  38  using a plurality of shear pins  44   a  and  44   a , respectively. Shear pins  44   a  and designed to withstand higher shear forces than shear pins  44   b.    
         [0023]    The plug  10  lands in seat  42   b  wherein ring  22  of the plug engages with and seals against a tapered end of the opening seat. Fluid is substantially blocked from flowing downhole by the seal formed between the ring  22  of the plug and the tapered end of opening seat  42   b . As the fluid is continued to be pumped downhole, pressure builds up. Upon reaching a high enough pressure the shear pins  44   b  shear, thereby causing opening seat  42   b  to slide downward to a position whereby the ports  40  are no longer cover the opening seat  42   b . In this position, fluids pumped from the surface are allowed to be injected into the wellbore and/or subterranean formation. At a later time another plug (not shown) can be sent downhole to seat with closing seat  42   a  so as to activate the shearing of pins  44   a  and thereby slide closing seat  42   a  into a position whereby the ports  40  are once again blocked, i.e., into a position whereby the flow of fluid into the wellbore and/or subterranean formation is closed. 
         [0024]    In the next step, after the plug  10  has activated the opening seat  42   b  into position, the plug  10  may be moved further downhole for subsequent operation. This can be accomplished by increasing the pressure of the fluid being pumped downhole so as to cause the shear pins  24  attaching the ring  22  to the hub  20  to fail. Upon shearing of the pins  24 , the ring  22  will separate from the hub  20  and remaining part of the plug  10 . This enables the plug  10  to continue traveling downhole for subsequent use is activating another downhole tool. Once the ring  22  separates from the plug  10 , it remains engaged with the tapered portion of opening seat  42   b . More specifically, the generally tapered/concave shape of the ring  22  allows the fluid being pumped downhole to force the ring into engagement with the tapered portion of the opening seat  42   b .  FIG. 6  illustrates the condition where the plug  10  has separated from the ring  22  and forced downhole leaving the ring engaged in the opening seat  42   b.    
         [0025]    Once the plug  10  separates from the ring  22  and moves further downhole it eventually engages with a seat  44  attached to a lower tool  46 , as shown in  FIG. 7 . In particular, the hub  20  engages with a tapered inner surface of the seat  44  to form a seal between the seat  44  and plug  10 . The seal formed between the seat  44  and the hub  20  of the plug  10  blocks the flow of fluid further downhole. As the fluid is continued to be pumped under this blocked condition, pressure builds up enabling the plug  10  and/or seat  44  to activate an operation of the lower tool  46 . The seat  44  may optionally be a moveable sleeve. Once the downhole operation of the lower tool  46  has completed, the plug  10  may be removed, or in the case where the lower tool  46  is at the end of the casing string, the plug  10  may simply remain in place. There are a number of ways to remove the plug  10 , which are known in the art, including but not limited to drilling out the plug, and utilizing a degradable material. 
         [0026]    Although the present disclosure and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the disclosure as defined by the following claims.

Summary:
A downhole plug and method of activating multiple downhole tools in a subterranean formation are disclosed. The plug includes a detachable ring that enables the plug to land in and engage at least two different seats, each seat having a different profile. This in turn enables the plug to activate at least two separate downhole devices, one in an upper downhole tool and one in a lower downhole tool. The ring separates from the plug once a certain pressure is reached in the wellbore enabling the plug to travel downhole from the upper tool to the lower tool to activate the device in the lower downhole tool.