Patent Publication Number: US-11391115-B2

Title: Plug piston barrier

Description:
TECHNICAL FIELD 
     The exemplary embodiments disclosed herein relate generally to downhole tools for oil and gas wells, and, more specifically to a plug assembly that temporarily blocks fluid flow through the plug assembly and creates an air pocket between the tool and casing string. 
     BACKGROUND 
     During running casing in a horizontal well, it is desirable to float the casing to avoid drag between the casing and the wellbore by keeping a temporary air pocket between the tool and the joints of casing. Various temporary plugs have been developed for this purpose. One type of temporary plug includes a water column provided in the bore of a tubular member that is adjacent to and uphole of a plug of compressed salt. The compressed salt plug prevents the water column from flowing through the tubular string. An elastomer barrier is provided to separate the water column from the drilling fluid in the casing string uphole of the water column to avoid contaminating the water with drilling fluid. 
     When an operator desires to reestablish fluid flow through the casing string, fluid pressure is increased in the casing string until rupture discs in the plug assembly give way. The water then flows through channels in the plug assembly, which allows drilling fluid to rupture, or fragment, the elastomer barrier. The water then dissolves the salt plug, which then allows fluid to begin flowing through the casing string. 
     Although such salt plug assemblies are adequate to temporarily prevent flow of fluids through the casing string, pieces of the fragmented elastomeric barrier may clog or damage valves or other equipment located downhole in the wellbore. Therefore, there is a need for continuous improvements in the field of temporary plugs for use in the casing of oil and gas wells. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the exemplary disclosed embodiments, and for further advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a cross-sectional view of a plug assembly in the run-in position according to embodiments of the disclosure; 
         FIG. 2  is a cross-sectional view of a plug assembly during fluid flow according to embodiments of the disclosure. 
         FIG. 3  is a cutaway view of a plug assembly in the run-in position according to embodiments of the disclosure; 
         FIGS. 4A-4B  are cross-sectional views of a sleeve for a plug assembly according to embodiments of the disclosure; and 
         FIG. 5  is a schematic diagram of a plug assembly arranged in a horizontal casing string according to embodiments of the disclosure. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     The following discussion is presented to enable a person ordinarily skilled in the art to synthesize and use the exemplary disclosed embodiments. Various modifications will be readily apparent to those skilled in the art, and the general principles described herein may be applied to embodiments and applications other than those detailed below without departing from the spirit and scope of the disclosed embodiments as defined herein. Accordingly, the disclosed embodiments are not intended to be limited to the particular embodiments shown, but are to be accorded the widest scope consistent with the principles and features disclosed herein. 
     As mentioned above, the embodiments disclosed herein generally relate to a plug assembly for temporarily blocking the flow of fluids through the plug assembly and creating an air pocket within the casing string in an oil and gas well. This helps to float the casing while running in a horizontal well. The plug assembly may include an elastomer membrane that can be ruptured to permit fluid flow through an interior flowbore (i.e., fluid flow path) of the plug assembly when desired by an operator. The elastomer membrane may be attached or bonded to a sleeve adjacent to the middle sub that is pushed uphole when fluid flow through the interior flowbore is permitted (i.e., when the membrane is ruptured). As the sleeve moves uphole, portions of the ruptured membrane are dragged along with the sleeve, thereby removing the ruptured membrane out of the fluid flow path of the plug assembly. This prevents the ruptured membrane from being eroded and inadvertently forced downhole where membrane debris may clog or damage valves or other equipment in the well. 
       FIG. 1  is a partial cross-sectional view showing a plug assembly  100  according to an embodiment of the disclosure. The plug assembly  100  includes a top sub  101  coupled to a middle sub  102  which is coupled to a housing  103 . The housing  103  is, in turn, coupled to a bottom sub  104 . Each of the top, middle, and bottom subs, as discussed herein, should be understood as constituted of a generally tubular member with an interior bore through which fluid may flow as part of an overall downhole tubular string. 
     A plug  105  is positioned in housing  103  adjacent to and coaxial with bottom sub  104 . The plug  105  is typically made of salt, but any substance that easily dissolves in the presence of water or other fluids may be used for the plug  105 . A column of water  106 , referred to sometimes as a water piston, is present within the interior bore of middle sub  102  adjacent to salt plug  105 . The combination of the water piston  106  and salt plug  105  blocks fluid flow through the flowbore of the plug assembly  100 . 
     A thin membrane  107  separates the water piston  106  from the salt plug  105  to prevent premature dissolving of the salt plug. After the salt plug  105  dissolves, membrane  107  fragments into small pieces. Due to the thinness of membrane  107 , the small pieces of membrane are able to pass through valves downhole and flush out to the surface with the drilling fluid. 
     A debris barrier  110 , which may be an elastomer membrane, is positioned adjacent to and coaxially with the middle sub  102  such that drilling fluid in the interior bore of the top sub  101  is on one side of the barrier  110  while water in water piston  106  is on the other side of the barrier  110 . The elastomer membrane debris barrier  110  thus separates the drilling fluid from the water in water piston  106  and prevents the drilling fluid from contacting the water piston  106  prior to the time that an operator desires to establish fluid flow through the plug assembly  100 . This arrangement of components is referred to as the “run-in” configuration of the plug assembly  100  and reflects the state of the components as the assembly  100  is lowered into the wellbore of an oil and gas well. 
     The middle sub  102  is also provided with at least one water channel  108  (i.e., fluid channel) extending along a length of middle sub  102  in a housing thereof. One or more rupture discs  109  prevent water in water piston  106  from entering into one end of water channel  108 . The opposite end of water channel  108  is in fluid communication with a chamber  111  formed between top sub  101  and middle sub  102 , as shown in  FIG. 2 . That end of water channel  108  is normally blocked by a sleeve  112  (specifically, a downhole face thereof) circumferentially disposed on the top sub  101  during run-in of the plug assembly  100 , as shown in  FIG. 1 . 
     During run-in of the plug assembly  100 , and prior to the time the operator desires to establish fluid flow through the plug assembly  100 , the water in water piston  106  is prevented from flowing into water channel  108  by rupture disc  109  and also O-ring  118  in sleeve  112 . Rupture disc  109  may be any type of rupture disc known to those of skill in the art that are designed to rupture, thus allowing fluid flow, when fluid pressure in the flowbore of plug assembly  100  reaches a threshold rupture value. The rupture disc  109  thus serves as a valve in this embodiment. Other suitable valves may be used in different embodiments. The rupture pressure of rupture disc  109  is a matter of design choice and may depend on the particular characteristics of an oil and gas well. 
     As mentioned above, chamber  111  is formed between top sub  101  and middle sub  102  where the two subs overlap one another. Sleeve  112 , which may be a metal sleeve, is positioned within chamber  111  between top sub  101  and middle sub  102 . Sealing rings  114  and  118 , which may be O-rings, are provided on sleeve  112  between top sub  101  and middle sub  102  to ensure there is no premature leakage of either water from water piston  106  or drilling fluids at sleeve  112  or into the chamber  111  and water channel  108 . 
     In operation, the plug assembly  100  is run into the wellbore of the oil and gas well with bottom sub  104  being arranged on the tool so that it is downhole of top sub  101 . In this run-in position, depicted in  FIG. 1 , the water piston  106  and salt plug  105  serve to block any flow of drilling fluid through top sub  101  and into bottom sub  104 . 
     When fluid flow through plug assembly  100 , and thus through the casing string in the wellbore, is desired, pressure in the drilling fluid in the casing string is increased. The pressure increase in the drilling fluid is transmitted through elastomer membrane  110  and into water piston  106 . The water in water piston  106  further transmits the increased pressure to rupture disc  109 . When the hydraulic pressure in the well reaches the burst point of rupture disc  109 , the disc bursts, allowing water from water piston  106  to escape past the now-ruptured disc. The water then moves through gaps and interstices (not expressly labeled) between middle sub  102  and an outer housing thereof and enters water channel  108  (also called “gun drill”). As the water works into channel  108 , the pressure of the drilling fluid in top sub  101  causes elastomer membrane  110  to stretch until it exceeds its structural integrity limit and fails, typically fragmenting into a petal-shaped pattern. The drilling fluid in top sub  101 , having displaced the water in water piston  106 , then contacts the salt plug  105 , dissolving it, thereby allowing fluid flow through the casing string. 
     The water coming in under pressure into water channel  108  presses against the downhole face of sleeve  112 . The pressurized water in water channel  108  pushes sleeve  112  in the uphole direction along an outer surface of top sub  101  into chamber  111 . The pressure from the water in water channel  108  is just sufficient to unseal the O-rings  114  and  118  on sleeve  112  and allow the sleeve to move into chamber  111 . Once the O-rings unseal, drilling fluid pushes the sleeve  112  further into chamber  111 , dragging along the now-fragmented elastomer membrane  110  attached thereto. 
     In some embodiments, the fragmented elastomer membrane  110  may be dragged by sleeve  112  into a pocket area  115  where it may be held out of the fluid flow path. In these embodiments, the downhole portion of top sub  101  may be reduced in wall thickness relative the uphole portion (e.g., by about 0.5 to 1.0 inch) to create the pocket area  115  between sleeve  112  and a downhole end of top sub  101  where the two overlap. The pocket area  115  provides a place to temporarily store the fragmented elastomer membrane  110 , preventing pieces thereof from being carried downhole. 
       FIG. 2  shows a cross-sectional view of the plug assembly  100  from  FIG. 1  after fluid flow through the casing has been established. In this view, salt plug  105  has been dissolved by fluid flow through the flowbore of the plug assembly  100 , allowing drilling fluids to flow through the casing string. Pressure from the water now in water channel  108  (which water was previously in water piston  106 ) has forced sleeve  112  along top sub  101  in the uphole direction into chamber  111 . 
     Because the elastomer membrane  110  was bonded or otherwise attached to sleeve  112  when the sleeve moved into chamber  111 , the (fragmented) membrane  110  was dragged along therewith and deposited in pocket area  115 . The pocket area  115  provides cover for the fragmented elastomer membrane  110  between the sleeve  112  and the top sub  101 , keeping the membrane out of the flow path of the fluids flowing through plug assembly  100 . This helps prevent pieces of the fragmented elastomer barrier  10  from being carried away by the fluid flow through the downhole casing where they might otherwise clog the float collar valve (not shown) of the cementing tool or interfere with the operation of other downhole valves or equipment. 
       FIG. 3  shows a partial cutaway view of plug assembly  100  in the run-in position according to an embodiment of the disclosure. The figure again shows top sub  101 , bottom sub  104 , and middle sub  102 . It will be appreciated, however, that the disclosed embodiments are not limited to the use of specific subs, but any arrangement of tubular members may be used within a downhole tool provided the mechanism described herein operates to allow a sleeve to slide along a tubular member to withdraw a fragmented elastomer membrane from the fluid flow path through the tool. For example, sleeve  112  could be provided on a tubular member, such as a housing, that is arranged inside the top sub  101  or other tubular member in the string. Therefore, there could be any number of tubular members located between top sub  101  and bottom sub  104  so long as the sleeve is allowed to move and withdraw the fragmented membrane from the flow path. 
     Further, although sleeve  112  is depicted in  FIG. 3  as a cylindrical sleeve, it will be appreciated that other arrangements, such as a ring provided with fingers for holding the elastomer membrane  110 , are possible. It will also be appreciated that the rupture disc  109  only illustrates one particular embodiment, and other valves may be employed to allow fluid to flow into fluid channel  108  to move the sleeve  112 . 
       FIG. 4A  is a cross-sectional view of an exemplary embodiment of sleeve  112  illustrating how the elastomer membrane  110  may be bonded or otherwise attached to sleeve  112 . As can be seen, sleeve  112  is provided with O-rings  114  that help provide a seal between top sub  101  and middle sub  102  (see  FIG. 1 ) and O-ring  118  that helps provide a seal between the sleeve and water channel  108 . Membrane  110  is bonded or otherwise attached to sleeve  112  via a T-shaped slot  110 A formed in the sleeve. The T-shaped slot  110 A can be seen in  FIG. 4B  with membrane  110  removed for clarity. Other slot shapes and/or other attachment techniques, including chemical and mechanical techniques (e.g., adhesive, fasteners, etc.), may certainly be used within the scope of the present disclosure. 
       FIG. 5  shows a plug assembly  500  according to embodiments of the present disclosure similar to the plug assembly  100  of  FIG. 1 , but arranged in a horizontal section of casing as it would be used in a drilling operation. In this embodiment, the plug assembly  500  is arranged within a larger section of casing string  501 . The upper section  503  of the casing string is filled with drilling fluid  502 . The drilling fluid is prevented from entering the lower section  504  of the casing string by the plug assembly  500 . Below the plug assembly  500  is chamber SOS. There may also be additional equipment, such as a float shoe and collar, valves, and other equipment (not shown) in the lower section of the casing string  504 . Portions of the lower section  504  of casing string  501  may also be filled with light weight fluid, such as a fluid lighter than drilling mud  502 . The result is that the lower section  504  of the casing string is buoyant in the wellbore, which reduces the drag between the casing and the formation. This increases the possible running depth of the casing, and minimizes the chances of the casing buckling or sticking. 
     As the foregoing demonstrates, the embodiments disclosed herein may be implemented in a number of ways. For example, in one aspect, embodiments of the present disclosure relate to a plug assembly for temporarily blocking fluid flow in a casing string of an oil and gas well. The plug assembly comprises, among other things, a top sub having an interior bore, a bottom sub disposed downhole of the top sub and having an interior bore, and a middle sub coupled to the top sub and the bottom sub therebetween. The middle sub has an interior bore, a fluid channel extending along a length of the middle sub, and a valve that, when opened, allows fluid to flow from the interior bore of the middle sub into the fluid channel. The plug assembly further comprises a sleeve mounted coaxially between the top sub and the middle sub adjacent to the fluid channel, the sleeve having a debris barrier attached thereto and positioned adjacent to the middle sub, the debris barrier separating the interior bore of the middle sub from the interior bore of the top sub. The sleeve is configured to move uphole along the top sub in response to fluid pressure in the fluid channel such that the debris barrier is withdrawn from a fluid flow path through the interior bores of the top sub and the middle sub. 
     In accordance with any one or more of the foregoing embodiments, the valve is opened in response to fluid pressure in the interior bore of the middle sub, the valve comprises a rupture disc, and/or the debris barrier comprises an elastomer membrane. 
     In accordance with any one or more of the foregoing embodiments, the plug assembly further comprises a dissolvable plug adjacent to and coaxial with the middle sub, the dissolvable plug preventing fluid flow through the plug assembly to thereby maintain an air pocket between the plug assembly and the casing string. 
     In accordance with any one or more of the foregoing embodiments, the dissolvable plug comprises compressed salt, the sleeve and the top sub define a pocket area between the sleeve and a downhole end of the top sub and the debris barrier is withdrawn into the pocket area when the sleeve moves uphole along the top sub, and/or the sleeve moves by sliding along a portion of the top sub in response to fluid pressure in the fluid channel. 
     In general, in another aspect, embodiments of the present disclosure relate to an apparatus for temporarily preventing fluid flow through a casing string in an oil and gas well. The apparatus comprises, among other things, a first tubular member, and a second tubular member coupled to the tubular member and having a valve that, when opened, permits fluid flow from an interior of the second tubular member into a fluid channel of the second tubular member. The apparatus further comprises a sleeve arranged coaxially between the first tubular member and the second tubular member adjacent to the fluid channel, the sleeve configured to slide over an outer surface of the first tubular member in response to fluid pressure in the fluid channel, the sleeve having an elastomer member attached thereto that serves to separate an interior of the first tubular member from the interior of the second tubular member. 
     In accordance with any one or more of the foregoing embodiments, the valve is opened in response to fluid pressure in the interior of the second tubular member, and/or the valve comprises a rupture disc. 
     In accordance with any one or more of the foregoing embodiments, the sleeve and the first tubular member define a pocket area therebetween and the elastomer member is dragged into the pocket area when the sleeve slides over the outer surface of the first tubular member, and/or the first and second tubular members define a chamber therebetween to receive the sleeve when the sleeve slides over the outer surface of the first tubular member in response to fluid pressure in the fluid channel. 
     In accordance with any one or more of the foregoing embodiments, the apparatus further comprises a removable plug adjacent to and coaxial with the second tubular member, and the removable plug comprises compressed salt that can be dissolved by fluid in the interior of the first and second tubular members. 
     In general, in yet another aspect, embodiments of the present disclosure relates to a method of temporarily plugging fluid flow through a tubular string of an oil and gas well. The method comprises, among other things, providing a first tubular member, and coupling a second tubular member to the first tubular member, the second tubular member having a valve that, when opened, permits fluid flow from an interior of the second tubular member into a fluid channel of the second tubular member. The method further comprises mounting a sleeve between the first tubular member and the second tubular member, the sleeve configured to slide over an outer surface of the first tubular member in response to fluid pressure in the fluid channel, the sleeve having an elastomer member attached thereto that serves to separate the interior of the first tubular member from the interior of the second tubular member. 
     In accordance with any one or more of the foregoing embodiments, the method further comprises opening the valve by increasing hydraulic pressure in the interior of the first and second tubular members, and/or sliding the sleeve over the outer surface of the first tubular member using fluid pressure in the fluid channel 
     In accordance with any one or more of the foregoing embodiments, the valve is a rupture disc and opening the valve comprises rupturing the rupture disc, and/or the elastomer member is withdrawn from a fluid flow path through the interiors of the first and second members when the sleeve slides along the first tubular member. 
     Further, although reference has been made to uphole and downhole directions, it will be appreciated that this refers to the run-in direction of the tool, and that the tool is useful in horizontal casing run applications, and the use of the terms of uphole and downhole are not intended to be limiting as to the position of the plug assembly within the downhole formation. 
     While the invention has been described with reference to one or more particular embodiments, those skilled in the art will recognize that many changes may be made thereto without departing from the spirit and scope of the description. Each of these embodiments and obvious variations thereof is contemplated as falling within the spirit and scope of the claimed invention, which is set forth in the following claims.