Abstract:
The present invention generally relates to a method and an apparatus for selectively isolating a portion of a wellbore. In one aspect, an apparatus for isolating a zone in a wellbore is provided. The apparatus includes a body having a bore. The apparatus further includes a first flapper member and a second flapper member, each flapper member selectively rotatable between an open position and a closed position. Additionally, the apparatus includes a flapper latch assembly disposed in the bore, the flapper latch assembly movable between an unlocked position and a locked position, wherein the flapper latch assembly is configured to hold the first flapper member in the closed position when the flapper latch assembly is in the locked position. In another aspect, a method for selectively isolating a zone in a wellbore is provided. In yet a further aspect, a flapper latch assembly for use with a flapper valve is provided.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation-in-part of U.S. patent application Ser. No. 11/761,229, filed Jun. 11, 2007 now U.S. Pat. No. 7,673,689, which claims benefit of U.S. provisional patent application Ser. No. 60/804,547, filed Jun. 12, 2006. Each of the aforementioned related patent applications is herein incorporated by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   Embodiments of the present invention generally relate to a wellbore tool for selectively isolating a zone in a wellbore. More particularly, the invention relates to a flapper latch for use with the wellbore tool. 
   2. Description of the Related Art 
   A completion operation typically occurs during the life of a well in order to allow access to hydrocarbon reservoirs at various elevations. Completion operations may include pressure testing tubing, setting a packer, activating safety valves or manipulating sliding sleeves. In certain situations, it may be desirable to isolate a portion of the completion assembly from another portion of the completion assembly in order to perform the completion operation. Typically, a ball valve, which is referred to as a formation isolation valve (FIV), is disposed in the completion assembly to isolate a portion of the completion assembly. 
   Generally, the ball valve includes a valve member configured to move between an open position and a closed position. In the open position, the valve member is rotated to align a bore of the valve member with a bore of the completion assembly to allow the flow of fluid through the completion assembly. In the closed position, the valve member is rotated to misalign the bore in the valve member with the bore of the completion assembly to restrict the flow of fluid through the completion assembly, thereby isolating a portion of the completion assembly from another portion of the completion assembly. The valve member is typically hydraulically shifted between the open position and the closed position. 
   Although the ball valve is functional in isolating a portion of the completion assembly from another portion of the completion assembly, there are several drawbacks in using the ball valve in the completion assembly. For instance, the ball valve takes up a large portion of the bore in the completion assembly, thereby restricting the bore diameter of the completion assembly. Further, the ball valve is susceptible to debris in the completion assembly which may cause the ball valve to fail to operate properly. Additionally, if the valve member of the ball valve is not fully rotated to align the bore of the valve member with the bore of the completion assembly, then there is no full bore access of the completion assembly. 
   There is a need therefore, for a downhole tool that is less restrictive of a bore diameter in a completion assembly. There is a further need for a downhole tool that is debris tolerant. There is a further need for a downhole tool having a flapper latch assembly that is configured to maintain a flapper valve in a closed position. 
   SUMMARY OF THE INVENTION 
   The present invention generally relates to a method and an apparatus for selectively isolating a portion of a wellbore. In one aspect, an apparatus for isolating a zone in a wellbore is provided. The apparatus includes a body having a bore. The apparatus further includes a first flapper member and a second flapper member disposed in the bore, each flapper member selectively rotatable between an open position and a closed position multiple times, wherein the first flapper member is rotated from the open position to the closed position in a first direction and the second flapper member is rotated from the open position to the closed position in a second direction. Additionally, the apparatus includes a flapper latch assembly disposed in the bore, the flapper latch assembly movable between an unlocked position and a locked position, wherein the flapper latch assembly is configured to hold the first flapper member in the closed position when the flapper latch assembly is in the locked position. 
   In another aspect, a method for selectively isolating a zone in a wellbore is provided. The method includes positioning a downhole tool in the wellbore, the downhole tool having a body, a first flapper member, a second flapper member and a flapper latch assembly, whereby each flapper member is initially in an open position. The method also includes moving the first flapper member to a closed position by rotating the first flapper member in a first direction. Further, the method includes moving the second flapper member to a closed position by rotating the second flapper member in a second direction. Additionally, the method includes moving a flapper latch assembly from an unlocked position to a locked position, whereby the flapper latch assembly is configured to hold the first flapper member in the closed position when the flapper latch assembly is in the locked position. 
   In yet a further aspect, a flapper latch assembly for use with a flapper valve is provided. The flapper latch assembly includes a body rotatable between an unlocked position and a locked position, wherein the body includes an end configured to engage a portion of the flapper valve when the flapper valve is in a closed position and the body is in the locked position. Additionally, the method includes a biasing member attached to the body, wherein the biasing member is configured to bias the body in the locked position. 

   
     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 cross-sectional view illustrating a downhole tool with a first flapper valve and a second flapper valve. 
       FIG. 2  is a cross-sectional view illustrating a flapper latch assembly for use with the first flapper valve. 
       FIG. 3  is a cross-sectional view illustrating the flapper latch assembly in an unlocked position and the first flapper valve in a closed position. 
       FIG. 4  is a cross-sectional view illustrating the flapper latch assembly in a locked position. 
       FIG. 5  is a cross-sectional view illustrating the flapper latch assembly in an unlocked position. 
       FIG. 6  is a cross-sectional view illustrating the first flapper valve and the second flapper valve in an open position and the flapper latch assembly in the unlocked position. 
       FIGS. 7 and 8  are cross-sectional views illustrating the actuation of a release mechanism in the flapper latch assembly. 
   

   DETAILED DESCRIPTION 
     FIG. 1  is a cross-sectional view illustrating a downhole tool  100 . The tool  100  includes an upper sub  105 , a housing  160 , and a lower sub  110 . The upper sub  105  is configured to be connected to an upper completion assembly (not shown), such as a packer arrangement. The lower sub  110  is configured to be connected to a lower completion assembly (not shown). Generally, the tool  100  is used to selectively isolate the upper completion assembly from the lower completion assembly. 
   The tool  100  includes a first flapper valve  125  and a second flapper valve  150 . The valves  125 ,  150  are movable between an open position and a closed position multiple times. As shown in  FIG. 1 , the valves  125 ,  150  are in the open position when the tool  100  is run into the wellbore. Generally, the valves  125 ,  150  are used to open and close a bore  135  of the tool  100  in order to selectively isolate a portion of the wellbore above the tool  100  from a portion of the wellbore below the tool  100 . 
   The valves  125 ,  150  may move between the open position and the closed position in a predetermined sequence. For instance, in a closing sequence, the first flapper valve  125  is moved to the closed position and then the second flapper valve  150  is moved to the closed position as will be described in relation to  FIGS. 2-4 . In an opening sequence, the second flapper valve  150  is moved to the open position and then the first flapper valve  125  is moved to the open position as will be described in relation to  FIGS. 5-6 . The particular sequence facilitates proper functioning of the tool  100 . For example, in the opening sequence, the second flapper valve  150  is moved to the open position first in order to allow the second flapper valve  150  to open in a substantially clean environment defined between the flapper valves  125 ,  150 , since the first flapper valve  125  is configured to substantially block debris from contacting the second flapper valve  150  when the first flapper valve  125  is in the closed position. In the closing sequence, the first flapper valve  125  is moved to the closed position first in order to substantially protect the second flapper valve  150  from debris that may be dropped from the surface of the wellbore. It must be noted that the valves  125 ,  150  may be operated according to other suitable sequences. 
   As illustrated in  FIG. 1 , the first flapper valve  125  is held in the open position by an upper flow tube  140 , and the second flapper valve  150  is held in the open position by a lower flow tube  155 . It should be noted that the flapper valves  125 ,  150  may be a curved flapper valve, a flat flapper valve, or any other suitable valve without departing from principles of the present invention. Further, the opening and closing orientation of the valves  125 ,  150  may be rearranged into any configuration without departing from principles of the present invention. Additionally, the second flapper valve  150  may be positioned at a location above the first flapper valve  125  without departing from principles of the present invention. 
   The tool  100  also includes a shifting sleeve  115  with a profile  165  proximate one end and a profile  190  proximate another end. The tool  100  further includes a spring  120  and a shift and lock mechanism  130 . As discussed herein, the shift and lock mechanism  130  interacts with the spring  120 , the shifting sleeve  115 , and the upper tubes  140 ,  155  in order to move the flapper valves  125 ,  150  between the open position and the closed position. 
   As shown in  FIG. 1 , the shift and lock mechanism  130  is a key and dog arrangement, whereby a plurality of dogs move in and out of a plurality of keys formed in the sleeves as the sleeves are shifted in the tool  100 . The movement of the dogs and the sleeves causes the flapper valves  125 ,  150  to move between the open position and the closed position. It should be understood, however, that the shift and lock mechanism  130  may be any type of arrangement capable of causing the flapper valves  125 ,  150  to move between the open and the closed position without departing from principles of the present invention. For instance, the shift and lock mechanism  130  may be a motor that is actuated by a hydraulic control line or an electric control line. The shift and lock mechanism  130  may be an arrangement that is controlled by fiber optics, a signal from the surface, an electric line, or a hydraulic line. Further, the shift and lock mechanism  130  may be an arrangement that is controlled by a pressure differential between an annulus and a tubing pressure or a pressure differential between a location above and below the tool  100 . 
     FIG. 2  is a cross-sectional view illustrating a flapper latch assembly  300  for use with the first flapper valve  125 . As will be described in relation to  FIGS. 3-8 , the flapper latch assembly  300  is generally configured to lock the first flapper valve  125  in the closed position. The flapper latch assembly  300  includes a body  305 , a release mechanism  310 , a biasing member  315 , and a pin member  325 . As shown, the flapper latch assembly  300  is in an unlocked position. 
     FIG. 3  is a cross-sectional view illustrating the flapper latch assembly  300  in the unlocked position and the first flapper valve  125  in a closed position. In the closing sequence, the first flapper valve  125  is moved to the closed position first in order to protect the second flapper valve  150  from debris that may be dropped from the surface of the wellbore. Referring back to  FIG. 1 , in one embodiment, a shifting tool (not shown) having a plurality of fingers that mates with the profile  165  of the shifting sleeve  115  is used to move the first flapper valve  125  to the closed position. The shifting tool may be a mechanical tool that is initially disposed below the tool  100  and then urged through the bore  135  of the tool  100  until it mates with the upper profile  165 . The shifting tool may also be a hydraulic shifting tool that includes fingers that selectively extend radially outward due to fluid pressure and mate with the profile  165 . In either case, the shifting tool mates with the profile  165  in order to pull the shifting sleeve  115  toward the upper sub  105 . 
   As the shifting sleeve  115  begins to move toward the upper sub  105 , the shift and lock mechanism  130  starts the closing sequence of the flapper valves  125 ,  150 . During the closing sequence, the shift and lock mechanism  130  moves the upper flow tube  140  away from the first flapper valve  125  in a direction as indicated by an arrow  230 . A biasing member (not shown) attached to a flapper member  185  in the first flapper valve  125  rotates the flapper member  185  around a pin  175  until the flapper member  185  contacts and creates a sealing relationship with a valve seat  170 . As illustrated, the flapper member  185  closes away from the lower sub  110 . As such, the first flapper valve  125  is configured to seal from below. In other words, the first flapper valve  125  is capable of substantially preventing fluid flow from moving upward through the tool  100 . In addition, as the shifting sleeve  115  moves toward the upper sub  105 , the spring  120  is also compressed. 
   As illustrated in  FIG. 3 , the flapper latch assembly  300  is in the unlocked position and the first flapper valve  125  is in the closed position. As the shifting tool urges the sleeve further toward the upper sub, the flapper latch assembly  300  is activated to secure the first flapper valve  125  in the closed position. The flapper latch assembly  300  may be configured to allow the first flapper valve  125  to burp or crack open if necessary. This situation may occur when debris from the surface of the wellbore falls and lands on the first flapper valve  125 . It should be noted that the flapper latch assembly  300  is not configured to allow the first flapper valve  125  to move to the full open position, unless a release mechanism is activated, as shown in  FIGS. 7-8 , but rather the flapper latch assembly  300  will only allow the first flapper valve  125  to crack open slightly. As such, the first flapper valve  125  in the closed position acts a barrier member to the second flapper valve  150  by substantially preventing large particles (i.e. a dropped drill string) from contacting and damaging the second flapper valve  150 . 
     FIG. 4  is a cross-sectional view illustrating the flapper latch assembly  300  in a locked position. After the first flapper valve  125  is in the closed position and secured in place, the shifting tool continues to urge the sleeve toward the upper sub, thereby causing the flapper valves  125 ,  150  and the flapper latch assembly  300  to move together as a subsystem relative to the housing  160  in a direction as indicated by an arrow  235 . The flapper latch assembly  300  moves in the housing  160  until the flapper latch assembly  300  is positioned proximate a recess  340  formed in the housing  160 , thereby allowing the flapper latch assembly  300  to move from the unlocked position to the locked position. At that point, the biasing member  315  causes the body  305  to rotate around the pin member  325  to allow the flapper latch assembly  300  to engage an end portion  145  of the first flapper valve  125 . At the same time, the second flapper valve  150  is moved in the housing  160  away from the lower flow tube  155 , thereby allowing a flapper member in the second flapper valve  150  to rotate around a pivot point until the flapper member contacts and creates a sealing relationship with a valve seat  180 . The flapper member closes away from the upper sub. As such, the second flapper valve  150  is configured to seal from above. In other words, the second flapper valve  150  is capable of substantially preventing fluid flow from moving downward through the tool  100 . Thereafter, the shifting sleeve  115  is urged closer to the upper sub  105  and the flapper valves  125 ,  150  are held in the closed position by the shift and lock mechanism  130 . Also, the spring  120  is in a full compressed state. 
   To open the valves  125 ,  150  according to one opening sequence, the second flapper valve  150  is moved to the open position first in order to allow the second flapper valve  150  to open in a clean environment by manipulating the shift and lock mechanism  130 . As discussed herein, in one embodiment, the shift and lock mechanism  130  is a key and dog arrangement, whereby the plurality of dogs move in and out of the plurality of keys formed in the sleeves as the sleeves are shifted in the tool  100 . The movement of the dogs and the sleeves causes the flapper valves  125 ,  150  to move between the open and the closed position. It should be understood, that the shift and lock mechanism  130  is not limited to this embodiment. Rather, the shift and lock mechanism  130  may be any type of arrangement capable of causing the flapper valves  125 ,  150  to move between the open and the closed position. 
   Prior to moving the second flapper valve  150  to the open position, the pressure around the second flapper valve  150  may be equalized by aligning a port (not shown) with a slot (not shown) formed in the flow tube  155  as the shifting sleeve  115  is moved toward the lower sub  110 . Thereafter, the further movement of the shifting sleeve  115  toward the lower sub  110  causes the flapper valves  125 ,  150  and the flapper latch assembly  300  to move together as a subassembly relative to the housing  160  in a direction as indicated by an arrow  240 . The flapper latch assembly  300  moves in the housing  160  until an edge  320  of the flapper body  305  contacts a slanted edge  330  in the housing  160 . At that point, the flapper latch assembly  300  moves to the unlocked position as the contact between the edge  320  and the slanted edge  330  causes the flapper body  305  to rotate around the pin member  325 , thereby causing the flapper latch assembly  300  to disengage from the end portion  145  of the flapper member  185 . At the same time, the second flapper valve  150  moves in the housing  160  toward the lower flow tube  155 . Contact of the second flapper valve  150  with the lower flow tube  155  overcomes a biasing member in the second flapper valve  150  such that the second flapper valve  150  moves from the closed position to the open position as shown in  FIG. 5 . As previously discussed, the movement of the shifting sleeve  115  toward the lower sub  110  may be accomplished by a variety of means. For instance, the shifting sleeve  115  may be urged toward the lower sub  110  by a hydraulic or mechanical shifting tool (not shown) that interacts with the profile  190  formed on the shifting sleeve  115 . In turn, the shifting sleeve  115  manipulates the mechanism  130  in order to open the flapper valves  125 ,  150 . 
     FIG. 6  is a cross-sectional view illustrating the first flapper valve  125  and the second flapper valve  150  in the open position and the flapper latch assembly  300  in the unlocked position. After the second flapper valve  150  is opened, the upper flow tube  140  moves toward the first flapper valve  125  as indicated by an arrow  245  as the shift and lock mechanism  130  is manipulated. Prior to the upper flow tube  140  contacting the flapper member  185  in the first flapper valve  125 , a slot (not shown) formed in the upper flow tube  140  aligns with a port (not shown) to equalize the pressure around the first flapper valve  125 . Thereafter, the upper flow tube  140  contacts the flapper member  185  in the first flapper valve  125  and causes the first flapper valve  125  to move from the closed position to the open position. Subsequently, the flapper valves  125 ,  150  are held in place by further manipulation of the shift and lock mechanism  130 . The process of moving the flapper valves  125 ,  150  between the open position and the closed position may be repeated any number of times. 
     FIGS. 7 and 8  are cross-sectional views illustrating the actuation of a release mechanism in the flapper latch assembly. While the flapper latch assembly  300  is in the locked position, the release mechanism  310  may be activated to allow the first flapper valve  125  to move from the closed position to the open position. The release mechanism  310  is generally activated by applying a force to the first flapper valve  125  in the direction as indicated by the arrow in  FIG. 7 . In turn, the force on the first flapper valve  125  causes a portion of the force to act upon the release mechanism  310 . At a predetermined force, the release mechanism  310  is activated, thereby allowing the first flapper valve  125  to move from the closed position to the open position as shown in  FIG. 8 . In one embodiment, the release mechanism  310  is a shearable member, such as a shear pin. In this embodiment, the shearable member is designed to fail at the predetermined force. It should be noted the predetermined force to activate the release mechanism  310  is generally less than a force that causes the pin  175  in the flapper latch  125  to fail. In this manner, the activation of the release mechanism  310  allows the first flapper valve  125  to move from the closed position to the open position. 
   In one embodiment, a hydraulic chamber arrangement is used to move the flapper valves. For instance, the flapper valves in the downhole tool are moved to the open position by actuating the shift and lock mechanism. In this embodiment, the shift and lock mechanism is actuated when a pressure differential between an ambient chamber and tubing pressure in the bore of the tool reaches a predetermined pressure. The chamber is formed at the surface between two seals. As the tool is lowered into the wellbore, a hydrostatic pressure is developed which causes a pressure differential between the pressure in the chamber and the bore of the tool. At a predetermined differential pressure, a shear pin (not shown) is sheared, thereby causing the spring to uncompress and shift the shifting sleeve toward the lower sub in order to release the flapper valves and start the opening sequence. The shear pin may be selected based upon the depth location in the wellbore that the shift and lock mechanism is to be actuated. 
   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.