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CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims benefit of U.S. provisional patent application Ser. No. 60/804,547, filed Jun. 12, 2006, which is herein incorporated by reference in its entirety. 
     
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    Embodiments of the present invention generally relate to wellbore completion. More particularly, the invention relates to a wellbore tool for selectively isolating a zone in a wellbore. 
         [0004]    2. Description of the Related Art 
         [0005]    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. 
         [0006]    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. 
         [0007]    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. 
         [0008]    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. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention generally relates to a wellbore tool for selectively isolating a portion of a wellbore from another portion of the wellbore. In one aspect, a method of selectively isolating a zone in a wellbore is provided. The method includes the step of positioning a downhole tool in the wellbore. The downhole tool includes a bore with a first flapper member and a second flapper member disposed therein, whereby each flapper member is initially in an open position. The method also includes the step of moving the first flapper member to a closed position by rotating the first flapper member in one direction. Further, the method includes the step of moving the second flapper member to a closed position by rotating the second flapper member in an opposite direction, whereby each flapper member is movable between the open position and the closed position multiple times. 
         [0010]    In another aspect, an apparatus for isolating a zone in a wellbore is provided. The apparatus includes a body having a bore formed therein. The apparatus also includes a first flapper member disposed in the bore. The first flapper member is 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 one direction. The apparatus further includes a second flapper member disposed in the bore. The second flapper member is selectively rotatable between an open position and a closed position multiple times, wherein the second flapper member is rotated from the open position to the closed position in an opposite direction. 
         [0011]    In yet another aspect, a method of isolating a first portion of a wellbore from a second portion of the wellbore is provided. The method includes the step of lowering a downhole tool in the wellbore. The downhole tool includes a first flapper member and a second flapper member, wherein each flapper member is initially in an open position and each flapper member is movable between the open position and a closed position multiple times. The method further includes the step of selectively isolating the first portion of the wellbore from the second portion of the wellbore by shifting the first flapper member to the closed position to hold pressure from below the first flapper member and shifting the second flapper member to the closed position to hold pressure from above the second flapper member. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    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. 
           [0013]      FIG. 1  is a cross-sectional view illustrating a downhole tool in a run-in position, wherein a first flapper valve and a second flapper valve are in an open position. 
           [0014]      FIG. 2  is a cross-sectional view illustrating the first flapper valve in a closed position. 
           [0015]      FIG. 3  is a cross-sectional view illustrating the second flapper valve in a closed position. 
           [0016]      FIGS. 4 and 5  are cross-sectional views illustrating a hydraulic chamber arrangement. 
           [0017]      FIGS. 6 and 7  are cross-sectional views illustrating the second flapper valve being moved to the open position. 
           [0018]      FIG. 8  is a cross-sectional view illustrating the first flapper valve in the open position. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]      FIG. 1  is a cross-sectional view illustrating a downhole tool  100  in a run-in position. 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. 
         [0020]    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 . 
         [0021]    The valves  125 ,  150  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. 1-3 . 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. 6-8 . The predetermined sequence allows the tool  100  to function properly. For example, in the opening sequence, the flapper valve  150  is moved to the open position first in order to allow the flapper valve  150  to open in a substantially clean environment defined between the flapper valves  125 ,  150 , since the flapper valve  125  is configured to substantially block debris from contacting the flapper valve  150  when the flapper valve  125  is in the closed position. In the closing sequence, the flapper valve  125  is moved to the closed position first in order to substantially protect the flapper valve  150  from debris that may be dropped from the surface of the wellbore. 
         [0022]    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 known flapper 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 flapper valve  150  may be positioned at a location above the flapper valve  125  without departing from principles of the present invention. 
         [0023]    The tool  100  includes a shifting sleeve  115  with a profile  165  proximate an end thereof and a profile  190  proximate another end thereof. The tool  100  also includes a biasing member  120 , such as a spring. The tool  100  further includes a shift and lock mechanism  130 . As discussed herein, the shift and lock mechanism  130  interacts with the biasing member  120 , the shifting sleeve  115 , and the flow tubes  140 ,  155  in order to move the flapper valves  125 ,  150  between the open position and the closed position. 
         [0024]    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  as illustrated in  FIGS. 1-3 . 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, 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 . 
         [0025]      FIG. 2  is a cross-sectional view illustrating the first flapper valve  125  in the closed position. In the closing sequence, the flapper valve  125  is moved to the closed position first in order to protect the flapper valve  150  from debris that may be dropped from the surface of the wellbore. In one embodiment, a shifting tool (not shown) having a plurality of fingers that mates with the profile  165  of the 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 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 sleeve  115  toward the upper sub  105 . 
         [0026]    As the sleeve  115  begins to move toward the upper sub  105 , the shift and lock mechanism  130  unlocks the flapper valves  125 ,  150 . Thereafter, the shift and lock mechanism  130  moves the flow tube  140  away from the flapper valve  125 . At that time, a biasing member (not shown) attached to a flapper member in the flapper valve  125  rotates the flapper member around a pivot point until the flapper member contacts and creates a sealing relationship with a valve seat  170 . As illustrated, the flapper member closes away from the lower sub  110 . As such, the flapper valve  125  is configured to seal from below. In other words, the flapper valve  125  is capable of substantially preventing fluid flow from moving upward through the tool  100 . In addition, as the sleeve  115  moves toward the upper sub  105 , the biasing member  120  is also compressed. 
         [0027]    As the shifting tool urges the sleeve  115  further toward the upper sub  105 , a locking mechanism  185  is activated to secure the flapper valve  125  in the closed position. The locking mechanism  185  may be any known locking mechanism, such as a ball and sleeve arrangement, pins, or a series of extendable fingers. The locking mechanism  185  is configured to allow the 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 flapper valve  125 . It should be noted that the locking mechanism  185  will not allow the flapper valve  125  to move to the full open position, as shown in  FIG. 1 , but rather the locking mechanism  185  will only allow the flapper valve  125  to crack open slightly. As such, the flapper valve  125  in the closed position acts a barrier member to the flapper valve  150  by substantially preventing large particles (i.e. a dropped drill string) from contacting and damaging the flapper valve  150 . 
         [0028]      FIG. 3  is a cross-sectional view illustrating the second flapper valve  150  in the closed position. After the flapper valve  125  is in the closed position and secured in place, the shifting tool continues to urge the sleeve  115  toward the upper sub  105 . At the same time, the flapper valve  150  is moved away from the flow tube  155 , thereby allowing a biasing member (not shown) attached to a flapper member in the flapper valve  150  to rotate the flapper member around a pivot point until the flapper member contacts and creates a sealing relationship with a valve seat  180 . As illustrated, the flapper member closes away from the upper sub  105 . As such, the flapper valve  150  is configured to seal from above. In other words, the flapper valve  150  is capable of substantially preventing fluid flow from moving downward through the tool  100 . Thereafter, the sleeve  115  is urged closer to the upper sub  105  and the flapper valves are locked in place by the shift and lock mechanism  130 . Also, the biasing member  120  is in a full compressed state. 
         [0029]      FIGS. 4 and 5  are cross-sectional views illustrating a hydraulic chamber arrangement. The flapper valves  125 ,  150  in the downhole tool  100  are moved to the open position by actuating the shift and lock mechanism  130 . In the embodiment illustrated in  FIGS. 4 and 5 , the shift and lock mechanism  130  is actuated when a pressure differential between an ambient chamber  210  and tubing pressure in the bore  135  of the tool  100  reaches a predetermined pressure. The chamber  210  is formed at the surface between two seals  215 ,  220 . As the tool  100  is lowered into the wellbore, a hydrostatic pressure is developed which causes a pressure differential between the pressure in the chamber  210  and the bore  135  of the tool  100 . As illustrated in  FIG. 5 , at a predetermined differential pressure, a shear pin  205  is sheared, thereby causing the biasing member  120  to uncompress and shift the sleeve  115  toward the lower sub  110  in order to unlock the flapper valves  125 ,  150  and start the opening sequence. The shear pin  205  may be selected based upon the depth location in the wellbore that the shift and lock mechanism  130  is to be actuated. 
         [0030]      FIGS. 6 and 7  are cross-sectional views illustrating the flapper valve  125  being moved to the open position. As previously set forth, in the opening sequence, the flapper valve  150  is moved to the open position first in order to allow the flapper valve  150  to open in a clean environment. However, prior to moving the flapper valve  150  to the open position, the flapper valves  125  and  150  are unlocked by manipulating the shift and lock mechanism  130 . Next, the pressure around the flapper valve  150  is equalized by aligning a port  230  with a slot  235  formed in the flow tube  155  as the sleeve  115  is moved toward the lower sub  110 . Thereafter, further movement of the sleeve  115  toward the lower sub  110  causes the flapper valve  150  to contact the flow tube  155  which will subsequently cause the flapper valve  150  to move from the closed position to the open position as shown in  FIG. 7 . As previously discussed, the movement of the sleeve  115  toward the lower sub  110  may be accomplished by a variety of means. For instance, the 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 sleeve  115 . In turn, the sleeve  115  manipulates the mechanism  130  in order to open the flapper valves  125 ,  150 . 
         [0031]    The flapper valves  125 ,  150  in the downhole tool  100  are moved to the open position 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  as illustrated in  FIGS. 1-3 . 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, such as a motor that is controlled by a hydraulic or electric control line from the surface. The shift and lock mechanism  130  may also 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 . 
         [0032]      FIG. 8  is a cross-sectional view illustrating the first flapper valve  125  in the open position. After the flapper valve  150  is opened, the flow tube  140  moves toward the flapper valve  125  as the shift and lock mechanism  130  is manipulated. Prior to the flow tube  140  contacting the flapper member in the flapper valve  125 , a slot  245  formed in the flow tube  140  aligns with a port  240  to equalize the pressure around the flapper valve  125 . Thereafter, the flow tube  140  contacts the flapper member in the flapper valve  125  and causes the flapper valve  125  to move from the closed position to the open position. Subsequently, the flapper valves  125 ,  150  are locked 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. 
         [0033]    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.

Summary:
The present invention generally relates to a wellbore tool for selectively isolating a portion of a wellbore from another portion of the wellbore. In one aspect, a method of selectively isolating a zone in a wellbore is provided. The method includes the step of positioning a downhole tool in the wellbore. The downhole tool includes a bore with a first flapper member and a second flapper member disposed therein, whereby each flapper member is initially in an open position. The method also includes the step of moving the first flapper member to a closed position by rotating the first flapper member in one direction. Further, the method includes the step of moving the second flapper member to a closed position by rotating the second flapper member in an opposite direction, whereby each flapper member is movable between the open position and the closed position multiple times. In another aspect, an apparatus for isolating a zone in a wellbore is provided.