Patent Publication Number: US-7896091-B2

Title: Convertible seal

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 11/623,141, filed Jan. 15, 2007, now U.S. Pat. No. 7,510,018, which is herein incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Embodiments of the present invention generally relate to a method and apparatus for selectively sealing the wellbore. More particularly, the apparatus relates to a seal that is convertible to a flow control seal. More particularly still, the apparatus relates to a seal having a plug and a valve, the valve being held in an open position upon run in and setting of the seal. More particularly still, the apparatus relates to a seal having a plug and a valve, the plug is removed when desired to allow the valve to control flow through the seal. 
     2. Description of the Related Art 
     In the drilling of oil and gas wells, a wellbore is formed using a drill bit that is urged downwardly at a lower end of a drill string. After drilling a predetermined depth, the drill string and bit are removed and the wellbore is lined with a string of casing. An annular area is thus formed between the string of casing and the wellbore. A cementing operation is then conducted in order to fill the annular area with cement. The combination of cement and casing strengthens the wellbore and facilitates the isolation of certain areas of the formation behind the casing for the production of hydrocarbons. 
     There are various downhole operations in which it may become necessary to isolate particular zones within the well. This is typically accomplished by temporarily plugging off the well casing at a given point or points with a bridge plug. Bridge plugs are particularly useful in accomplishing operations such as isolating perforations in one portion of a well from perforations in another portion or for isolating the bottom of a well from a wellhead. The purpose of the plug is simply to isolate some portion of the well from another portion of the well. Bridge plugs do not allow flow past the plug in either direction. In order to reestablish flow past a bridge plug an operator must remove and/or destroy the bridge plug by milling, drilling, or dissolving the bridge plug. 
     During a fracturing or stimulation operation of a production zone, it is often necessary to seal the production zone from wellbore fluids while allowing production fluids to travel up the wellbore and past the seal. Frac plugs are designed to act as a seal and to provide a fluid path therethrough. Frac plugs typically have a one way valve which prevents fluids from flowing downhole while allowing fluids to flow uphole. In operation, a frac plug is installed above the zone that has been fractured (frac&#39;d) or treated. This seals the treated zone from the uphole wellbore fluids while allowing any production fluids to flow through the frac plug. After the frac plug is set, an operator may treat an uphole zone without interfering with the previously treated downhole zone. Once the uphole zone is treated, a second frac plug may be set above it. This process may be repeated until all, or a select number, of the production zones in the wellbore have been treated. 
     In some instances, it may be desirable to seal a treated lower zone from flow in both directions while treating an upper zone. In particular, it is often desirable to reduce the wellbore pressure above the pressure-charged treated lower zone by setting a pressure isolation device and then bleeding off wellbore pressure at the surface. This is desirable for safety reasons as well as providing a negative pressure test on the plug, which is set above the treated zone. This is not possible using a frac plug. Instead, this requires setting a bridge plug above the treated zone. The pressure above the bridge plug is then bled off. The upper zone may then be treated while flow to the lower zone is prevented. After the upper zone has been treated, the bridge plug is removed and a frac plug is set in its place. The removal of the bridge plug and setting of the frac plug generally requires separate trips downhole. Each trip adds to the expense of the operation. Further, the time required to set the frac plug after the bridge plug is removed may cause damage to the lower zone due to wellbore pressure entering the treated zone. 
     There is a need, therefore, for a bridge plug which can be converted to a frac plug. There is a further need for the bridge plug to have a valve which is mechanically held in the open position until the bridge plug is converted to a frac plug. 
     SUMMARY OF THE INVENTION 
     Embodiments described herein relate to a convertible seal. The convertible seal may be for use in a wellbore. The convertible seal may have a seal element for sealing the interior of the wellbore and a fluid path through the sealing element. Further, the convertible seal may include a removable plug configured to block fluid communication through the fluid path and a valve in fluid communication with the fluid path. In addition, the convertible seal may include an activator configured to hold the valve in an open position while the removable plug blocks the fluid path. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
         FIG. 1  is a schematic view of a wellbore having a convertible seal according to one embodiment described herein. 
         FIG. 2  is a schematic view of a convertible seal according to one embodiment described herein. 
         FIG. 3  is a cross sectional view of a convertible seal according to one embodiment described herein. 
         FIG. 3A  is a cross sectional view of an end of the convertible seal according to one embodiment described herein. 
         FIG. 4  is a cross sectional view of a convertible seal according to one embodiment described herein. 
         FIG. 5  is a schematic view of a wellbore having a convertible seal according to one embodiment described herein. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a schematic view of a wellbore  100  according to one embodiment described herein. The wellbore  100  includes a tubular  102  having an annulus  104  between the wellbore and the tubular  102 . The tubular  102 , as shown, is a casing; however, it should be appreciated that the tubular  102  could be any downhole tubular such as, but not limited to, a liner, a production tubing, or a drill string. The annulus  104 , as shown, is filled with cement; however, it should be appreciated that cementing is not required and that other means for isolating the wellbore  100  may be used, such as expanding the casing into the wellbore and external packers. 
     Although shown as having a casing, it should be appreciated that the wellbore may be an open hole wellbore. 
     The wellbore  100  intersects at least one production zone  105 . A rig  106  having a rig floor  108  is located at the surface. The rig  106  may be used to form a conveyance  110  and, thereafter, run the conveyance  110  into the wellbore  100 . The conveyance  110 , as shown, is a jointed pipe which is formed by coupling pipe stands together at the surface, then lowering each pipe stand into the wellbore  100  and attaching a subsequent pipe. Although shown as a jointed pipe, it should be appreciated that the conveyance  110  may be any conveyance for running tools, for example a production tubing, a drill string, a casing, coiled tubing, a co-rod, a wire line, or a slick line. It is contemplated that the conveyance  110  may be run in by other methods, for instance by winding and unwinding a spool with a conveyance such as coiled tubing, wire line, slick line, or rope. 
     The conveyance  110  is shown running a convertible seal  112  into the wellbore  100 . The convertible seal  112  is adapted to set inside the tubular  102  or uncased wellbore and seal the interior diameter of the tubular  102 . Initially upon setting of the convertible seal  112 , the tubular  102  is sealed from flow past the convertible seal  112  in either up-hole flow or down-hole flow direction. When desired, the convertible seal  112  may be converted to allow controllable flow, as described in more detail below. 
       FIG. 2  is a schematic view of the convertible seal  112  in sealing engagement with the tubular  102 . The convertible seal  112  may be used initially as a bi-directional seal and later converted to a unidirectional flow control seal. The convertible seal  112  includes a seal  200 , a plug  202 , a valve  204 , and an activator  206 . The seal  200  has a flow path  208  which transverses the seal  200 . The seal  200  is configured to fluidly seal the interior diameter of the tubular  102 . The plug  202  is configured to block the flow path  208  from fluid communication. The plug  202  is operatively coupled to a lower portion of the seal  200  using one or more selectively releasable pins  210 . Although shown as pins  210 , any device for temporarily coupling the plug  202  to the seal  200  may be used, including but not limited to a collet, a shearable ring. The valve  204  positioned at an upper portion of the seal  202  is in fluid communication with the flow path  208 . The valve  204  may be held in the open position by the activator  206  until the plug  202  is removed from the flow path  208 . After the plug  202  is removed and the activator  206  is no longer holding the valve  204  in the open position, the valve  204  may be operated to control fluid flow past the seal  200 , as will be described in more detail below. Thus, the convertible seal  112  may be run into a wellbore  100  and set at the desired location. The set convertible seal  112  seals bi-directional fluid flow in the wellbore  100 . Thereafter, the plug  202  may be removed and the valve  204  used to control fluid flow. 
       FIG. 3  is a cross sectional view of the convertible seal  112  coupled to the conveyance  110 , according to one embodiment. In addition to the valve  204 , the seal  200 , the activator  206 , and the plug  202 , the convertible seal  112  includes a connector portion  300 , an actuator  302 , and a mandrel  304 . The connector portion  300  is adapted for coupling the convertible seal  112  to the conveyance  110 . As shown, the connector portion  300  is a threaded connection; however, it should be appreciated that any suitable connection for coupling the convertible seal  112  to the conveyance  110  may be used. 
     The seal  200 , as shown in  FIG. 3 , is a packer having a sealing element  306  and one or more gripping members  308 . The sealing element  306  is an annular member disposed around the mandrel  304  and between two wedge blocks  310 . The wedge blocks may be used to compress the sealing element  306 , thereby forcing the sealing element  306  to expand radially outward and into engagement with the tubular  102 , as will be discussed in more detail below. The sealing element  306  may have any number of configurations to effectively seal the annulus created between the mandrel  304  and a tubular  102 . The sealing element  306  may include grooves, ridges, indentations, or protrusions designed to allow the sealing element  306  to conform to variations in the shape of the interior of the tubular  102 . The sealing element  306  may be constructed of any expandable or otherwise malleable material which creates a set position and stabilizes the mandrel  304  relative to the tubular  102 . For example, the sealing element  306  may be a metal, a plastic, an elastomer, or a combination thereof. Further, the sealing element  306  may be an inflatable sealing member. 
     The gripping members  308  as shown in  FIG. 3  are slips; however, it should be appreciated that the gripping members  308  may be any device adapted to engage the interior of the tubular. Alternatively, the gripping member may be absent and the sealing element is adapted to grip the tubular  102 . The gripping members  308  have an angled surface  314  adapted to engage a corresponding angled surface  316  of the wedge block  310 . As the gripping members move, the angled surface  314  and the corresponding angled surface  316  interact to move the gripping members  308  radially away from the longitudinal axis of the convertible seal  112 . The radial movement causes the gripping members  308  to engage and grip the tubular  102 . 
     The actuator  302  may include a setting piston  318  adapted to move the slips in the longitudinal direction. The setting piston  318  has a shear pin  320  which holds the piston  318  in place until the packer is to be set. Force is delivered to the actuator  302  via an electric line setting tool, a hydraulic setting tool or is mechanically applied. The actuator  302  exerts a force on the piston  318 . When the force is greater than the force required to shear the shear pin  320 , the shear pin  320  is sheared and the piston  318  moves in order to operate the packer. It should be appreciated that the actuator may be any actuator capable of setting the seal  200  in the tubular  102 . 
     The plug  202 , as shown, is adapted to seal the bore  312  of the convertible seal  112  until the plug  202  is removed. The plug  202  has a seal-ring  326  adapted to fluidly seal any space between the mandrel  304  and the plug  202 . The plug  202  further includes one or more shear pins  328  to hold the plug  202  in place until it is desired to remove the plug  202 . Although shown as one or more shear pins  328  any device for temporarily holding the plug  202  may be used including, but not limited to, a collet and/or a shearable ring. The plug  202  may be any material capable of containing fluid pressure, including but not limited to, metal, plastic, composite, or cement. It should be appreciated that the plug  202  may be any structure which seals the bore  312  and the flow path  208  and is capable of being removed once in the wellbore. 
     The activator  206  is adapted to hold the valve  204  in the open position until the plug  202  is removed. In one embodiment, the activator  206  is coupled to the plug  202  such that removal of the plug  202  will deactivate the activator  206 , thereby allowing the valve  204  to close. As shown, the activator  206  is a rod that is used to keep the valve  204  open. The rod is supported on the plug  202  and extends through and out of the flow path  208 . The activator  206  may be any structure capable of keeping the valve  204  open. The activator  206  may be made of any material including, but not limited to, metal, composite, plastic, an elastomer, a cement, or any combination thereof. The activator  206  is shown as a rigid member; however, it should be appreciated that it could be a flexible member or a biasing member such as a spring. 
     The valve  204  may be a one way ball valve having a ball  330  and a ball seat  332 . The activator  206  holds the ball  330  off of the ball seat  332  until the plug  202  is removed. After the plug  202  is removed, the ball  330  is free to engage the ball seat  332  thereby sealing the flow path  208 . The valve  204  is adapted to seal the flow path  208  when the pressure above the valve  204  is greater than the pressure below the valve  204 . A stopper  334  may be used to prevent the ball  330  from traveling up and out of the convertible seal  112 , but the stopper  334  should not significantly impede flow of fluid in the bore  312 . Although shown as a ball valve, it should be appreciated that the valve  204  may be any suitable valve capable of remaining open until the plug  202  is removed and then acting as a one-way valve. Further, the valve may be any valve including, but not limited to, a one-way valve, a flapper valve, a counterbalanced valve, or a poppet/seat-style valve. 
       FIG. 3A  is a cross sectional view of the plug  202  and the mandrel  304  at line A-A. The mandrel  304  may include a profile  336  configured to receive a protrusion  338  of the plug  202 . The profile  336  and the protrusion  338  are optional and are adapted to inhibit the plug  202  from sealingly re-entering the mandrel  304  once the plug  202  has been removed. That is, when the plug  202  is released from the mandrel  304  it slides or is forcefully expelled past a shoulder  340 , and the protrusion  338  disengages the profile  336 . In order for the plug  202  to sealingly re-enter mandrel  304 , the protrusion  338  and the profile  336  would have to be in alignment with one another. Therefore, even with the introduction of fluid pressure below the plug  202 , it is unlikely that the plug  202  will sealingly re-engage the mandrel  304 . The protrusion  338  may take any form so long as it assists in preventing the plug  202  from re-entering the mandrel  304 . Some alternative designs of the protrusion  338 , and/or the profile  336 , include, but are not limited to, a biased member, such as a leaf spring, or an elastomeric, which expands once the plug  202  is past the shoulder  340 . 
     In operation, the convertible seal  112  is run into the wellbore  100  on the conveyance  110 . A fracturing or treatment operation may be performed below the convertible seal  112 . The actuator  302  shears the shear pins  320  to release the piston  318 . The piston  318  then moves in response to the actuator  302 . The piston  318  urges the gripping member  308  against the wedge blocks  310 . As the gripping member  308  moves, a third set of shear pins  342  holding the wedge blocks  310  in place is sheared. The upper wedge blocks  310  then move into contact with the sealing element  306 . The sealing element  306  pushes against the lower wedge block  310  and the shear pin  342  for the lower wedge block  310  is sheared. The lower wedge block  310  then engages the lower gripping member  308  thereby forcing it radially outward. As the piston  318  continues to move under pressure, the wedge blocks  310  move the gripping members  308  into engagement with the tubular  102 , as shown in  FIG. 4 . The wedge blocks  310  also compress the sealing element  306 , thereby forcing the sealing element  306  into sealing engagement with the tubular  102 . In this respect, the annulus  400  between the convertible seal  112  and the tubular  102  is sealed from fluid flow in both directions. Further, the plug  202  prevents fluid from flowing past the convertible seal  112  through the fluid path  208 . In this configuration, the convertible seal  112  acts as a bridge plug. 
     The convertible seal  112  may remain in the tubular  102  as a bridge plug until desired. The conveyance  110  may be removed and operations may be performed uphole of the convertible seal  112 . When it is desired to convert the convertible seal  112 , fluid pressure is increased above the convertible seal  112 . The increased fluid pressure enters the fluid path  208  past the valve  204 , which is held open by the activator  206 , and exerts a force on the top surface of the plug  202 . The fluid pressure is increased until the shear pins  328  are sheared. The plug  202  is then free to move in response to the fluid pressure. The plug  202  is forced down by the fluid pressure force until it is clear of the shoulder  340 . As the plug  202  moves down, the activator  206  also moves down, thereby allowing the ball  330  to move down. With the plug  202  clear of the shoulder  340 , fluid may pass the plug  202  before the valve  204  is closed. The ball  330  eventually lands on the ball seat  332  and further fluid pressure applied up-hole of the convertible seal  112  keeps the valve  204  in the closed position. The convertible seal  112  now operates like a frac plug. That is, the valve  204  of the convertible seal  112  prevents wellbore fluids that are uphole of the convertible seal  112  to flow past the valve  204 . However, if the fluid pressure below the convertible seal  112  is greater than the fluid pressure above the convertible seal  112 , the valve  204  allows the higher pressure fluid to pass up through the valve  204 . The plug  202  may be prevented from moving back into sealing engagement with the mandrel  304  due to the improbability that the plug  202  will align with the mandrel  304  above the shoulder  340  and/or through use of the protrusion  338 . Any number of convertible seals  112  may be used in one wellbore  100  as shown in  FIG. 5 . 
     In an alternative embodiment, the activator  206  is a biased member, such as a spring or an elastomer. The biasing member may have a minimum fixed length. At the minimum fixed length the biasing member will prevent the valve  204  from closing when the plug  202  is fixed in the mandrel  304 . The biasing member functions to extend the plug  202  beyond the end of the mandrel  304  once the plug  202  is sheared, thereby eliminating possible re-engagement and sealing of the plug  202 . With the plug  202  sheared from the mandrel, and the valve  204  in the closed position, the activator  206  will bias the plug  202  beyond the shoulder  340 , thereby ensuring that the plug  202  does not reseal the mandrel  304 . Further, it is contemplated that a spring or plug biasing member may be used independently of the activator in order to expel the plug  202  from the mandrel  304 . In this instance the plug biasing member may exert less force on the plug than is required to shear the plug  202  from the mandrel  304 . Once the plug  202  is free from the mandrel, the plug biasing member exerts sufficient force to expel the plug  202  from the mandrel  304 . 
     In yet another alternative embodiment, any location requiring a restricted flow path to be converted to a controllable flow path at some time in the future may use a two valve seal. In this embodiment, a mechanical member, for example a rod, holds two valves apart thereby preventing both valves from being closed at the same time. Thus, a first valve is initially in the closed position and the mechanical member is preventing the second valve from closing. A force is then applied to the first valve in order to open the first valve. The force may be the result of fluid pressure, mechanical pressure, or electric actuation. With the first valve open, the mechanical member no longer prevents the second valve from closing. Thus, the second valve is now free to control flow in the valve. 
     The embodiments described herein are not limited to use in a wellbore. The embodiments described herein may be used at any flow control location, including, but not limited to, piping systems, pipelines, tubing, etc. 
     While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.