Abstract:
The present invention generally relates to downhole tools. More particularly, the invention relates to a locking mechanism for use on a downhole tool. A flow actuated locking mechanism is provided for a downhole tool that includes an annular, two-position sleeve having an unlocked position and a locked position. A pin assembly within the tool is used to retain the sleeve in the locked position. In one aspect of the invention, the locking mechanism is used on a reaming tool with extendable cutters that are extendable from the body of the tool to increase the diameter of the tool and aid in forming a wellbore therearound. The locking mechanism prevents the cutters from collapsing or closing as the reamer is moved axially in the wellbore.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention generally relates to an apparatus and methods for drilling, completion and rework of wells. More particularly, the invention relates to an apparatus and method for activating and releasing downhole tools. More particularly still, the invention provides an internal pressure indicator and locking mechanism for the downhole tool. 
   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 tubular string. After drilling to a predetermined depth, the tubular string and bit are removed, and the wellbore is lined with a string of steel pipe called casing. The casing provides support to the wellbore and facilitates the isolation of certain areas of the wellbore adjacent to hydrocarbon bearing formations. The casing typically extends down the wellbore from the surface of the well to a designated depth. An annular area is thus defined between the outside of the casing and the earth formation. During the completion process, this annular area is filled with cement to permanently set the casing in the wellbore and to facilitate the isolation of production zones and fluids at different depths within the wellbore. 
   Various downhole tools are used throughout the well completion process. One such downhole tool is a conventional under-reamer. Generally, the conventional under-reamer is used to enlarge the diameter of wellbore by cutting away a portion of the inner diameter of the existing wellbore. A conventional under-reamer is typically run downhole on a tubing string to a predetermined location with the under-reamer blades in a closed position. Subsequently, fluid is pumped into the conventional under-reamer and the blades extend outward to contact the surrounding wellbore. Thereafter, the blades are rotated through hydraulic means and the front blades enlarge the diameter of the existing wellbore as the conventional under-reamer is urged further into the wellbore. 
   The conventional under-reamer may also be used in a back-reaming operation. In the same manner as the under-reaming operation, fluid is pumped into the under-reamer and the blades are extended outward into contact with the surrounding wellbore. Thereafter, the blades are rotated through hydraulic means and the back blades enlarge the diameter of the existing wellbore as the under-reamer is pulled toward the surface of the wellbore. However, if the blades are not securely locked in place, the upward pulling of the under-reamer causes the blades to fluctuate between an inward and outward position, thereby creating an uneven hole. 
   A blade locking mechanism on a conventional under-reamer includes a mandrel with a taper. The mandrel is moved between a first and a second position by a spring. Typically, the mandrel uses the mechanical advantage of the taper to apply a force on a piston to keep the blades in the fully open position. The amount of taper on the mandrel is critical to reduce the coefficient of friction at the mandrel and blade interface. For example, if the taper on the mandrel is too small, the spring will be unable to pull the mandrel from the second position to the first position, thereby causing the conventional under-reamer to become immobilized downhole. On the other hand, if the taper is too large, the mechanical advantage of the mandrel is diminished, thereby reducing the force on the piston. In either case, due to downhole conditions, the coefficient of friction on moving parts can vary greatly, making this method of locking the blades open very unpredictable. 
   Typically, fluid pumped through the conventional under-reamer is used to move the mandrel from the first position to the second position. In the second position, the mandrel acts against the cam mechanism to open the blades. As the mandrel slides on a body of the conventional under-reamer toward the second position, a plurality of bypass holes are exposed in the body allowing some fluid to flow out of the conventional under-reamer resulting in a lower pressure in the conventional under-reamer. This lower pressure is used as an indicator to the operator that the blades are open because the mandrel is in the second position. There are several problems associated with the use of bypass holes as an indicator. One problem relates to the less positive indication. In this method, the bypass holes are exposed as the mandrel travels on the body, which may cause time flutter and throttling at low flow rates. Another problem is that this method permits a less accurate indication of the exact position of the blades during actuation of the conventional under-reamer. 
   There is a need therefore, for an under-reamer that includes a positive lock mechanism to ensure the blades remain open during a back reaming operation. There is a further need therefore, for an under-reamer that includes a locking mechanism that is predictable. There is a further need for an under-reamer that includes an indicator that permits an accurate indication of the exact position of the blades during actuation of the under-reamer. 
   SUMMARY OF THE INVENTION 
   The present invention generally relates to downhole tools. More particularly, the invention relates to a locking mechanism for use on a downhole tool. A flow actuated locking mechanism is provided for a downhole tool that includes an annular, two-position sleeve having an unlocked position and a locked position. A pin assembly within the tool is used to retain the sleeve in the locked position. In one aspect of the invention, the locking mechanism is used on a reaming tool with extendable cutters that are extendable from the body of the tool to increase the diameter of the tool and aid in forming a wellbore therearound. The locking mechanism prevents the cutters from collapsing or closing as the reamer is moved axially in the wellbore. In another aspect of the invention, a signal to the surface of the well is producible based upon the position of the locking mechanism. In one embodiment, a central bore of the tool is restricted when the mechanism is in an unlocked position and is less restricted when the mechanism is in the locked position. Utilizing this variable restriction, an operator at the surface of the well can determine, based upon back-pressure, the position of the tool in the wellbore. 

   
     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 tool in a run-in position. 
       FIG. 2A  is a cross-sectional view illustrating the tool blades in the open position. 
       FIG. 2B  is a cross-sectional view illustrating locking pins in an open position. 
       FIG. 3  illustrates the first stage in the unlocking sequence as the unlocking sleeve begins to urge the locking pins radially inward. 
       FIG. 4  illustrates the second stage of the unlocking sequence as the connection pins contact an end portion of the cam. 
       FIG. 5  illustrates the third stage of the unlocking sequence as the end portion of the cam contacts the upper portion of the locking pins. 
       FIG. 6A  is a cross-sectional view illustrating the tool unlocked and the blades in the closed position. 
       FIG. 6B  is a cross-sectional view illustrating locking pins in a closed position. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1  is a cross-sectional view illustrating a tool  100  in a run-in position. As shown, the tool  100  is an under-reamer. Generally, the under-reamer is used to enlarge the diameter of an existing wellbore by cutting away a portion of the inner diameter. It should be noted that the invention is not limited to an under-reamer, but may be employed with other downhole tools that require a positive locking mechanism and a flow indicator. 
   As illustrated in  FIG. 1 , the tool  100  includes a sub  215  at the upper end. The sub  215  is used to connect to a string of tubulars (not shown) at a connection  245 . The sub  215  also includes a sub bore  220  to allow fluid communication through sub  215 . As shown, the sub  215  is connected to a body  105 . The body  105  includes a center bore  110  that is fluidly connected with the sub bore  220  to allow the fluid entering the tool  100  to exit out ports  120 . 
   A housing  260  is disposed around the body  105  and the sub  215 . The housing  260  is moveable between a first position and a second position by fluid pressure. As depicted, a port  270  in the body  105  is in fluid communication with a cavity  275  formed between the sub  215  and a housing surface  280 . As fluid flows through the tool  100 , a portion of fluid in the center bore  110  is communicated through the port  270  into the cavity  275 . As more fluid enters the cavity  275 , the pressurized fluid acts against the housing surface  280  to urge the housing  260  from the first position to the second position. 
   As illustrated on  FIG. 1 , a piston  185  is disposed around the body  105  and connected to the housing  260 . The piston  185  is movable between a first position and a second position. As shown, a port  195  in the body  105  is in fluid communication with a cavity  285  formed between a ring  305  and a piston surface  190 . As fluid flows through the tool  100 , a portion of fluid from the center bore  110  is communicated through the port  195  into the cavity  285 . As more fluid enters the cavity  285 , the pressurized fluid acts against the piston surface  190  to urge the piston  185  from the first position to the second position. At that time, the force against the piston surface  190  overcomes an opposite force created by biasing member  115 , thereafter the piston  185  moves axially downward toward the second position compressing the biasing member  115  against a stop  180 . 
   The lower end of the piston  185  is connected to an unlocking sleeve  160  by connection pins  165 . The unlocking sleeve  185  includes a taper  170  at an upper end and a sleeve shoulder  265  at a lower end. The sleeve shoulder  265  is constructed and arranged to mate with a cam shoulder  140  on cam  155 . The cam  155  is arranged to shift blades  145  from the closed position to the open position upon activation of the tool  100 . 
   As further illustrated in  FIG. 1 , a plurality of locking pins  150  are disposed in a plurality of side bores  175 . The locking pins  150  are movable between an open and a closed position. In the closed position, as shown in  FIG. 1 , the locking pins  150  restrict the flow of fluid through the center bore  110  resulting in a higher pressure in the tool  100 . Each locking pin  150  includes an O-ring  230  disposed around the lower portion of the locking pin  150  to create a fluid tight seal between the locking pin  150  and the side bore  175 . 
     FIG. 2A  is a cross-sectional view illustrating the blades  145  in the open position. The fluid pumped down a tubular string (not shown) through the sub bore  270  enters the center bore  110 . Thereafter, the fluid in the center bore  110  is communicated to ports  270 ,  195  and subsequently into cavities  275 ,  285 . The fluid pressure in the cavities  275 ,  285  urge the housing  260 , the unlocking sleeve  160  and the piston  185  from the first position to the second position, thereby compressing biasing member  115  against stop  180 . At the same time, the sleeve shoulder  265  acts against the cam shoulder  140  to extend the blades  145  to the open position. 
   Additionally, the fluid pumped through the center bore  110  urges the locking pins  150  radially outward towards the open position. In the open position, an upper portion  130  of the locking pins  150  project out from the body  105 , thereby exposing a pin shoulder  225 . The pin shoulder  225  interacts with a cam surface  290  to prevent axial movement of the cam  155 . In this respect, the locking pins  150  act as a lock to ensure the cam  155  will not move axially, thereby allowing the blades  145  to remain open throughout the operation of the tool  100 . 
     FIG. 2B  is a cross-sectional view illustrating locking pins  150  in the open position. As shown, the locking pins  150  have moved radially outward away from the center bore  110 . In the open position, the locking pins  150  no longer restrict the flow through the center bore  110  resulting in a lower pressure in the tool  100 . The lower pressure corresponds to a predetermined pressure, which indicates to the operator that the blades  145  are fully extended to the open position. Conversely, the locking pins  150  in the closed position restricts the flow through the central bore  110  creating a higher pressure in the tool  100  to indicate to the operator that the blades are in the closed position. In this respect, the locking pins  150  act as an indicator to inform the operator whether the blades  145  are in the open position or in the closed position. 
   As clearly shown on  FIG. 2B , the locking pins  150  include a shear groove  125  at the upper portion  130 . The shear groove  125  is constructed and arranged to allow the upper portion  130  of the locking pins  150  to shear off at a predetermined force. Generally, if the tool  100  becomes immobilized downhole because the biasing member (not shown) or the unlocking sleeve (not shown) fails to function properly, the tool  100  may be removed by axially pulling up on the tool  100  and shearing the top portion of the locking pins  150 . In this respect, the shear groove  125  acts as a back-up means to remove the locking pins  150  from contact with the cam  155  and allow the tool  100  to be removed if the tool  100  fails to function properly. 
     FIG. 3  illustrates the first stage in the unlocking sequence as the unlocking sleeve  160  begins to urge the locking pins  150  radially inward. After the downhole operation is complete, flow through the tool  100  is reduced, thereby causing the biasing member  115  to expand. As the biasing member  115  expands, the piston  185 , pins  165  and the unlocking sleeve  160  are urged axially upward toward the sub (not shown). As the piston  185 , pins  165  and the unlocking sleeve  160  move from the second position to the first position, the taper  170  on the unlocking sleeve  160  contacts the upper portion  130  of the locking pins  150 , thereby urging the locking pins  150  radially inward toward the center bore  110 . Additionally, the sleeve shoulder  265  loses contact with the cam shoulder  140 , thereby allowing the cam  155  to begin releasing the blades  145 . 
     FIG. 4  illustrates the second stage of the unlocking sequence as the connection pins  165  contact an end portion  295  of the cam  155 . As the piston  185 , pins  165  and the unlocking sleeve  160  continue to move axially upward toward the sub (not shown), the connection pins  165  travel up slot  135  formed in the cam  155  until the pins  165  contact the end portion  295 . At that point, the axial upper movement of the piston  185 , pins  165  and unlocking sleeve  160  pulls the cam  155  away from the blades  145 , thereby allowing the blades  145  to move from the open position toward the closed position. As further shown in  FIG. 4 , the locking pins  150  are urged further inward toward the central bore  110  as the unlocking sleeve  160  moves across the upper portion  130  of the locking pins  150 . As the locking pins  150  restrict the flow through the center bore  110 , a higher pressure is created in the tool  100 . The higher pressure corresponds to a predetermined pressure, which indicates to the operator that the unlocking sequence is in the second stage. 
     FIG. 5  illustrates the third stage of the unlocking sequence as the end portion  165  of the cam  155  contacts the upper portion  130  of the locking pins  150 . As shown, the cam  155  has moved axially upward allowing the end portion  165  to contact the upper portion  130  to further urge the locking pins  150  inward toward the center bore  110 . As further shown, the blades  145  have started to retract inward to allow the tool  100  to be removed from the wellbore. 
     FIG. 6A  is a cross-sectional view illustrating the tool  100  unlocked and the blades  145  in the closed position. As shown, the tool  100  is in a deactivated state, the cam  155  has pushed the locking pins  150  to the closed position therefore ending the unlocking sequence. As further shown, biasing member  115  is uncompressed and the piston  185  is in the first position. Also shown, the blades  145  are completely closed allowing the tool  100  to be removed from the wellbore.  FIG. 6B  is a cross-sectional view illustrating locking pins  150  in a closed position. At this point, the operator may verify that the tool  100  is completely deactivated by pumping fluid through a tubular string (not shown) into the tool  100 . As the fluid encounters the locking pins  150  in the closed position, a higher pressure is created in the tool  100 . The higher pressure corresponds to a predetermined pressure, which indicates to the operator that the blades  145  are closed and the tool  100  is deactivated. 
   In operation, the tool is lowered on a tubular string to a predetermined location in the wellbore. Thereafter, fluid is pumped down the tubular string through the sub bore and enters the center bore. The fluid in the center bore is communicated to ports in the body and subsequently into cavities. The fluid pressure in the cavities urge the housing, the unlocking sleeve and the piston from the first position to the second position, thereby compressing a biasing member against a stop. At the same time, the sleeve shoulder acts against the cam shoulder to extend the blades to the open position. 
   The fluid pumped through the center bore also urges the locking pins radially outward towards the open position. In the open position, an upper portion of the locking pins project out from the body, thereby exposing a pin shoulder. The pin shoulder interacts with a cam surface to prevent axial movement of the cam. In this respect, the locking pins act as a lock to ensure the cam will not move axially, thereby allowing the blades to remain open throughout the operation of the tool. 
   After the downhole operation is complete, flow through the tool is reduced causing the biasing member to expand and begin the first stage of the unlocking sequence. As the biasing member expands, the piston, connection pins and the unlocking sleeve are urged axially upward toward the sub. As the piston, connection pins and the unlocking sleeve move from the second position to the first position, the taper on the unlocking sleeve interacts with the upper portion of the locking pins, thereby urging the locking pins radially inward toward the center bore. Additionally, the sleeve shoulder loses contact with the cam shoulder, thereby allowing the cam to begin the release of the blades. 
   In the second stage of the unlocking sequence, the connection pins contact an end portion of the cam. As the piston, connection pins and the unlocking sleeve continue to move axially upward toward the sub, the connection pins travel up slot formed in the cam until the connection pins contact the end portion of the slot. At that point, the axial upper movement of the piston, connection pins and unlocking sleeve pulls the cam away from the blades, thereby allowing the blades to move from the open position toward the closed position. Additionally, the locking pins are urged further inward toward the central bore as the unlocking sleeve moves across the upper portion of the locking pins. As the locking pins restrict the flow through the center bore, a higher pressure is created in the tool. The higher pressure corresponds to a predetermined pressure, which indicates to the operator that the unlocking sequence is in the second stage. In the third stage of the unlocking sequence, the end portion of the cam contacts the upper portion of the locking pins to further urge the locking pins inward toward the center bore. 
   After the unlocking sequence is complete, the blades are closed and the locking pins are in the closed position. At this point, the operator may verify that the tool is completely deactivated by pumping fluid through a tubular string into the tool. As the fluid encounters the locking pins in the closed position, a higher pressure is created in the tool. The higher pressure corresponds to a predetermined pressure, which indicates to the operator that the blades are closed and the tool is deactivated. Thereafter, the tool may be removed from the wellbore. 
   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.