Abstract:
The present invention generally relates to an apparatus and method of forming a wellbore. In one aspect, an expandable bit for use in a wellbore is provided. The expandable bit includes a body and a blade assembly disposed on the body. The blade assembly is movable between a closed position whereby the expandable bit has a smaller outer diameter and an open position whereby the expandable bit has a larger outer diameter. The expandable bit further includes a release assembly for providing a secondary means to move the blade assembly from the open position to the closed position. In another aspect, a method of forming a wellbore is provided. In yet another aspect, an expandable apparatus for use in forming a wellbore is provided.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention generally relates to wellbore construction. More particularly, the invention relates to an apparatus and method for deactivating a downhole tool. More particularly still, the invention relates to an expandable bit with a secondary release device. 
   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. The drill bit generally includes a body portion for securing the drill bit to the drill string and a crown portion to form the wellbore. After drilling a predetermined depth, the drill string and the drill bit are removed, and the wellbore is lined with a string of steel pipe called casing. The casing typically includes a smaller outside diameter than the drill bit that formed the wellbore. The casing provides support to the wellbore and facilitates the isolation of certain areas of the wellbore adjacent 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. 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. 
   In a conventional completion operation, it is common to employ more than one string of casing in a wellbore. In this respect, the well is drilled to a second designated depth of a smaller diameter, and a second string of casing, or liner, is run into the drilled out portion of the wellbore. The second string is set at a depth such that the upper portion of the second string of casing overlaps the lower portion of the first string of casing and then cemented in place. This process is typically repeated with additional casing strings until the well has been drilled to a total depth. As more casing strings are set in the wellbore, the casing strings become progressively smaller in diameter in order to fit within the previous casing string. In the conventional completion operation, the drill bits must be progressively smaller as the diameter of each casing string decreases in order to fit within the previous casing string. 
   From time to time, for a variety of reasons it is necessary to form a portion of a wellbore that is at least as large as the section of the cased wellbore thereabove. For example, a monobore well consist of a sequence of expandable liners that are run through the existing casing, then expanded to achieve the same post-expansion through-bore. In forming the monobore well, the portion of the wellbore below the cased portion must be at least as large as the section of the cased wellbore thereabove. 
   There are a variety of different methods of forming an enlarged wellbore. One such method is by positioning a conventional under-reamer behind the drill bit to cut the enlarged wellbore. In this drilling configuration, the drill bit acts as a pilot bit to cut the inner cross-sectional area while the under-reamer enlarges the cross-sectional area. Generally, the conventional under-reamer includes a number of expandable arms that move between a closed position and an open position. The ability of the conventional under-reamer to open and close the arms allows the under-reamer in the closed position and the pilot bit to travel though a smaller diameter casing. After passing through the casing the underreamer may be opened to form an enlarged diameter bore below the casing shoe resulting in a wellbore equal to or larger than the original drilled hole. Thereafter, the enlarged wellbore may be lined with expandable liners. This procedure of forming the enlarged borehole, although effective may be time consuming and expensive. 
   In recent years bi-center bits have been developed as an alternative to the conventional under-reamer. Generally, the bi-center bit includes offset cutting members mounted at irregular intervals around the crown of the bit. As the bi-center bit is rotated, the offset cutting members rotate to form an enlarged wellbore. Although, this method of forming an enlarged wellbore is becoming more common the bi-center bits are unstable due to their irregular structure and tend to be more difficult to control for directional purposes than ordinary drill bits. Additionally, the bi-center bits may not drill the expected swept diameter of the offset pads which ream the pilot hole created by the crown. 
   More recently, an expandable bit has been used to form an enlarged portion of the wellbore. The expandable bit was introduced to over come the deficiencies in the conventional under-reamer and the bi-center bit. An example of an expandable bit is disclosed in International Publication Number WO 01/81708 A1, which is incorporated herein in its entirety. Similar to the conventional under-reamer, the expandable bit includes a set of blades that move between an open position and a closed position. Generally, hydraulic fluid flows through the center of the expandable bit controls the movement of the blades between the open and the closed position. A more detailed discussion of the expandable bit will be described in subsequent paragraphs. 
   Even though the expandable bit overcomes many of the deficiencies in the conventional under-reamer and the bi-center bit, a problem still exists with the use of the expandable bit to form an enlarged wellbore. The problem includes the possibility that the expandable bit will become stuck in the open position due to some unforeseen event, like a failure in the hydraulic fluid flow or debris that causes the blades to become jammed. For example, the hydraulic fluid used to operate the tool may contain debris or other small particles intermixed with the fluid portion. As the hydraulic fluid flows through the expandable bit, the debris builds inside the tool and eventually may affect the closing of the expandable bit. 
   The problem results in the expandable bit being stuck downhole because the expandable bit cannot travel through the casing in the open position. When this problem occurs, an operator has several options, however, each option has significant drawbacks. One option is to remove the cemented casing string to access the stuck expandable bit. This option is very time consuming and costly. Another option is to cut the drill string and leave the stuck expandable bit downhole. Thereafter, the operator may drill around the stuck expandable bit or “side track” the well. Although this option is less destructive than the previous option, drilling around an obstruction requires special downhole tools that may not be available at the wellsite. Another option is to mill through the stuck expandable bit. This option is problematic because the expandable bit is constructed from hardened material, resulting in a difficult milling operation that requires replacing the mill tool multiple times. 
   In view of the deficiency of the expandable drill bit, a need therefore exists for an expandable bit with a release device to shift the blades from the open position to the closed position in the event of a primary means of closing the blades is unworkable. There is a further need for an expandable bit with a release device that allows the expandable bit to move to the closed position in the event that debris forces the blades to remain open. There is yet a further need for an improved expandable bit. 
   SUMMARY OF THE INVENTION 
   The present invention generally relates to an apparatus and method of forming a wellbore. In one aspect, an expandable bit for use in a wellbore is provided. The expandable bit includes a body and a blade assembly disposed on the body. The blade assembly is movable between a closed position whereby the expandable bit has a smaller outer diameter and an open position whereby the expandable bit has a larger outer diameter. The expandable bit further includes a release assembly for providing a secondary means to move the blade assembly from the open position to the closed position. 
   In another aspect, a method of forming a wellbore is provided. The method includes lowering a drill string with an expandable bit at the end thereof through a previously formed wellbore. The expandable bit includes a body, a blade assembly disposed on the body and a release assembly for providing a secondary means to move the blade assembly from the open position to the closed position. The method further includes causing the expandable bit to move from the closed position to the open position and rotating the expandable bit to form a lower portion of the wellbore. The method also includes applying an axial force to the expandable bit and the release assembly to move the blade assembly to the closed position and removing the drill string and the expandable bit from the wellbore. 
   In yet another aspect, an expandable apparatus for use in forming a wellbore is provided. The expandable apparatus includes a body and cutting members disposed on the body, the cutting members movable between a collapsed position and an expanded position. The expandable apparatus further includes a re-settable release member for allowing the cutting members to move between the expanded position to the collapsed position. 
   In another aspect, a method for drilling a portion of a wellbore is provided. The method includes lowering an expandable cutting apparatus in the wellbore and expanding the expandable cutting apparatus. The method also includes rotating the expandable cutting apparatus and drilling a portion of the wellbore and collapsing the expandable cutting apparatus. 

   
     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 an expandable bit disposed at a lower end of a drill string in a partially cased wellbore. 
       FIG. 2  is a cross-sectional view illustrating the expandable bit forming a lower portion of a wellbore. 
       FIG. 3  is a cross-sectional view illustrating the activation of a release assembly. 
       FIG. 4  is a cross-sectional view illustrating a hydraulic cylinder moving axially upward to release a blade pivot housing. 
       FIG. 5  is a cross-sectional view illustrating the expandable bit being removed from the wellbore. 
       FIG. 6A  is a cross-sectional view illustrating an expandable bit with a re-settable release assembly. 
       FIG. 6B  is an enlarged view of the re-settable release assembly. 
       FIG. 7A  is a cross-sectional view illustrating the activation of the re-settable release assembly. 
       FIG. 7B  is an enlarged view of the re-settable release assembly. 
       FIG. 8A  is a cross-sectional view illustrating the expandable bit after the re-settable release assembly releases the blade pivot housing. 
       FIG. 8B  is an enlarged view of the re-settable release assembly. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The present invention relates to a secondary release assembly for an expandable bit. Generally, the release assembly is constructed and arranged to release blade arms of the expandable bit upon the application of a force to the expandable bit. 
     FIG. 1  is a cross-sectional view illustrating the expandable bit  100  disposed at the lower end of a drill string  145  and run-in wellbore  150 . As illustrated, the wellbore  150  is lined with casing  135 . Generally, the expandable bit  100  may move between an open position and a closed position. In the open position, ( FIG. 2 ) arms  190  at the lower end of the expandable bit  100  are expanded outward while in the closed position the arms  190  are collapsed inward. The arms  190  are attached to a blade pivot housing  155  by a plurality of hinge pins  175 . The hinge pins  175  allow the arms  190  to swing out from a body  125  of the bit  100 . The arms  190  include a plurality of cutting elements  210  made of a hard material such as tungsten carbide or polycrystalline diamond. The arms  190  are constructed and arranged to permit the cutting elements  210  to contact and drill the earth when the arms  190  are expanded outward and not ream the wellbore or surrounding casing  135  when the arms  190  are collapsed inward. Each arm  190  may carry a single or double row of cutting elements  210  depending on the desired drilling configuration. 
   As shown in  FIG. 1 , nozzles  185  are arranged at the lower end of the body  125 . The nozzles  185  are in fluid communication with a bore  205  defined in the body  125  to communicate fluid through the expandable bit  100  and allow jetting of the drilling fluid during the drilling operation to remove any cutting build up that may gather in front of the arms  190 . The nozzles  185  are also used to create a hydraulic pressure differential within the bore  205  of the expandable bit  100  in order to cause the arms  190  to expand outward as will be discussed herein. 
   Movement of the arms  190  from the collapsed position to the expanded position occurs when a hydraulic pressure differential created across the nozzles  185  causes a hydraulic cylinder  120  to move axially upward drawing the arms  190  over a head  180 . Generally, as fluid is pumped through the expandable bit  100 , the nozzles  185  restrict the fluid flow causing the hydraulic pressure differential and urging a portion of fluid through port  110  formed in the body  125  to fill a chamber  105  defined between the hydraulic cylinder  120  and an internal piston  115 . As the chamber  105  fills with fluid, the volume of the chamber  105  increases, causing the hydraulic cylinder  120  to move axially upward compressing a biasing member  140 . At the same time, the hydraulic cylinder  120  draws the blade pivot housing  155  axially upward, thereby pulling the arms  190  over the head  180 . In this manner, the axial force created on the blade pivot housing  155  by the hydraulic cylinder  120  causes the arms  190  to pivot outwards at pins  175  to the expanded position and to remain in the expanded position as long as the hydraulic pressure differential is maintained in the body  125  of the expandable bit  100 . Additionally, guide pins  160  act on slots  170  machined in the arms  190  to ensure that the arms  190  return to the closed position upon removal of the hydraulic pressure differential. 
   Generally, the reduction of fluid flow reduces the pressure differential created by the nozzles  185 , thereby causing the fluid pressure in the chamber  105  to be reduced to a hydrodynamic pressure below that required to compress the biasing member  140 . In other words, the reduction of the fluid flow allows the biasing member  140  to expand and urge the hydraulic cylinder  120  and the blade pivot housing  155  axially downward pushing the arms  190  over the head  180  and into the collapsed position. 
   In addition to moving the arms  190  hydraulically, the expandable bit  100  also includes a release assembly  200 . The release assembly  200  is generally used in the event that the arms  190  fail to move to the collapsed position by the means previously described. In one embodiment, the release assembly  200  is a threaded connection between the hydraulic cylinder  120  and the blade pivot housing  155 . As illustrated on  FIG. 1 , threads machined on the hydraulic cylinder  120  are mated with threads machined on the blade pivot housing  155  to form the threaded connection. The threads on the hydraulic cylinder  120  and the blade pivot housing  155  are machined to a close fit tolerance. The threads are constructed and arranged to fail or shear when a predetermined axial force is applied to the expandable bit  100 . The desired axial force required to actuate the release assembly  200  determines the quantity of threads and the thread pitch. Generally, an axial force is applied to the expandable bit  100  to activate the release assembly  200 , thereby allowing the blade pivot housing  155  to move axially downward as will be discussed herein. 
   Alternatively, other forms of shearable members may be employed in the release assembly  200 , as long as they are capable of shearing at a predetermined force. For example, a shear pin (not shown) may be placed between the hydraulic cylinder  120  and the blade pivot housing  155 . The shear pin may be constructed and arranged to fail at a predetermined axial force. Generally, a shear pin is a short piece of brass or steel that is used to retain sliding components in a fixed position until sufficient force is applied to break the pin. Once the pin is sheared, the components may then move to operate or function the tool. 
     FIG. 2  is a cross-sectional view illustrating the expandable bit  100  forming a lower portion of the wellbore  150 . After the expandable bit  100  is placed at a desired location in the wellbore  150 , the expandable bit  100  may be placed in the open position by pumping fluid through the expandable bit  100 . Thereafter, the drill string  145  and the expandable bit  100  are rotated and urged axially downward to form the lower portion of the wellbore  150 . 
   In  FIG. 2 , the expandable bit  100  is shown the open position and fluid is used to maintain a hydraulic force on the internal piston  115  and the hydraulic cylinder  120 . The hydraulic cylinder  120  maintains the arms  190  in the expanded position as discussed in a previous paragraph. In addition to the hydraulic cylinder  120 , the drilling load of the expandable bit  100  also keeps the arms  190  in the expanded position. 
   There are any number of unforeseen wellbore conditions or equipment failure that can lead to the arms  190  being stuck in the expanded position. For example, drilling fluid pumped through the expandable bit  100  may contain debris or other small particles intermixed with the fluid portion. The debris collects in the chamber  105  as more fluid enters the chamber  105  to create the required hydraulic force to move the hydraulic cylinder  120  axially upward. The debris does not necessarily affect the drilling operation while the arms  190  are maintained in the expanded position as shown in FIG.  2 . However, after the drilling operation is complete, the debris will typically prevent the chamber  105  from decreasing in volume after the fluid flow is reduced, thereby preventing any axial movement of the hydraulic cylinder  120 . 
     FIG. 3  is a cross-sectional view illustrating the activation of the release assembly  200 . As shown, the arms  190  are in the expanded position, thereby preventing the removal of the expandable bit  100  from the wellbore  150  due to its outer diameter. As discussed previously, any number of unforeseen wellbore conditions or equipment failure can lead to the arms  190  being stuck in the expanded position. To activate the release assembly  200 , the drill string  145  and the expandable bit  100  are pulled axially upwards allowing the arms  190  to contact a lower end of the casing  135 . As the drill string  145  and the expandable bit  100  continue to be pulled upward, an axial force is created on the release assembly  200 . At a predetermined force, the threaded connection between the hydraulic cylinder  120  and the blade pivot housing  155  fails activating the release assembly  200 . 
     FIG. 4  is a cross-sectional view illustrating the hydraulic cylinder  120  moving axially upward to release the blade pivot housing  155 . After the release assembly  200  is activated, the hydraulic cylinder  120  continues to move axially upward until the threads on the hydraulic cylinder  120  and the threads on the blade pivot housing  155  are no longer engaged. At this point, the blade pivot housing  155  may move axially downward pushing the arms  190  over the head  180  and subsequently move into the collapsed position as shown on FIG.  5 . 
     FIG. 5  is a cross-sectional view illustrating the expandable bit  100  being removed from the wellbore  150 . As shown, the threads on the hydraulic cylinder  120  no longer contact the threads on the blade pivot housing  155  and the chamber  105  remains in the expanded state. As further shown, the arms  190  are in the collapsed position, thereby allowing the expandable bit  100  to be removed from the wellbore  150 . 
   While the embodiment in  FIGS. 1-5  illustrate the expandable bit  100  with a one-time release assembly  200 , an expandable bit with a release assembly that may be used multiple times may also be employed in the wellbore  150 .  FIGS. 6A and 6B  are a cross-sectional view illustrating an expandable bit  300  with a re-settable release assembly  350 . For convenience, components on the expandable bit  300  that are similar to the components on the expandable bit  100  will be referenced with the same numbers. Generally, the re-settable release assembly  350  allows the blade pivot housing  155  to collapse the arms  190  upon an application of an axial force and thereafter allows the blade pivot housing  155  to expand the arms  190  upon application of an opposite axial force. In other words, the re-settable release assembly  350  allows the blade pivot housing  155  to release the arms  190  multiple times. 
   As illustrated in  FIG. 6B , the re-settable release assembly  350  includes a split ring  305  with a tapered edge  310 . Generally, the split ring  305  is constructed of a metallic material that biases the split ring  305  radially outward. During operation of the expandable bit  300 , the split ring  305  is disposed in a groove  330  formed in the hydraulic cylinder  120 . The groove  330  includes a tapered edge  335  that mates with the tapered edged  310  formed on the split ring  305 . Additionally, a tapped hole  340  disposed adjacent the groove  330  allows a screw (not shown) to urge the split ring  305  radially inward for manual disassembly of the re-settable release assembly  350 . 
     FIGS. 7A and 7B  are a cross-sectional view illustrating the activation of the re-settable release assembly  350 . As shown, the arms  190  are in the expanded position, thereby preventing the removal of the expandable bit  300  from the wellbore  150  due to its outer diameter. As discussed previously, any number of unforeseen wellbore conditions or equipment failure can lead to the arms  190  being stuck in the expanded position. To activate the re-settable release assembly  350 , the drill string  145  and the expandable bit  300  are pulled axially upwards allowing the arms  190  to contact a lower end of the casing  135 . As the drill string  145  and the expandable bit  300  continue to be pulled upward, an axial force is created on the re-settable release assembly  350 . The axial force causes the hydraulic cylinder  120  to move axially away from the blade pivot housing  155 . At the same time, the tapered edge  335  in the hydraulic cylinder  120  acts against the tapered edge  310  formed on the split ring  305  causing the split ring  305  to move radially inward toward a piston groove  320  formed in piston  315 . 
     FIGS. 8A and 8B  are a cross-sectional view illustrating the expandable bit  300  after the re-settable release assembly  350  releases the blade pivot housing  155 . As shown, the split ring  305  has moved radially inward into the piston groove  320  and an end of the hydraulic cylinder  120  is disposed adjacent the piston groove  320 , thereby containing the split ring  305  within the piston groove  320 . Also shown, the chamber  105  remains in the expanded state while the arms  190  are in the collapsed position allowing the expandable bit  300  to be pulled through the casing  135  or another obstruction. After the expandable bit clears the casing  135  or another obstruction, the expandable bit  300  may be re-set by applying a downward axial force on the expandable bit  300 . The axial force causes the hydraulic cylinder  120  to move axially downward aligning the groove  330  in the hydraulic cylinder  120  with the piston groove  320  in the piston  315 . At this point, the outwardly biased split ring  305  expands radially outward into the groove  330  and the blade pivot housing  155  causes the arms  190  to move from the collapsed position to the expanded position as previously illustrated in FIG.  6 A. In this manner, the re-settable release assembly  350  allows the arms  190  to move from the expanded position to the collapsed position and thereafter be reset without removing the expandable bit  300  from the wellbore  150 . 
   In operation, the expandable bit is attached at the lower end of a drill string. Thereafter, the drill string and expandable bit are placed at a desired location in the wellbore and fluid is pumped through the expandable bit. As the fluid flows through the expandable bit, the nozzles restrict the flow causing a hydraulic pressure differential in the bore of the expandable bit. The hydraulic pressure differential urges a portion of fluid through a port in the body of the expandable bit to fill a chamber defined between the hydraulic cylinder and internal piston. As the chamber fills with fluid, the volume of the chamber increases causing a hydraulic cylinder to move axially upward compressing a biasing member. At the same time, the hydraulic cylinder draws the blade pivot housing axially upward, thereby pulling the arms over the head and into the expanded position. Subsequently, the drill string and the expandable bit are rotated while being urged axially downward to form the lower portion of the wellbore. 
   After the drilling operation, the expandable bit is typically closed hydraulically by reducing the fluid flow through the expandable bit. Generally, the reduction of fluid flow reduces the pressure differential created by the nozzles, thereby causing the fluid pressure in the chamber to be reduced to a hydrodynamic pressure below that required to compress the biasing member. In other words, the reduction of the fluid flow allows the biasing member to expand and urge the hydraulic cylinder and the blade pivot housing axially downward pushing the arms over the head and into the collapsed position. However, there are any number of unforeseen wellbore conditions or equipment failure that can lead to the arms being stuck in the expanded position, thereby requiring the activation of the release assembly. 
   To activate the release assembly, the drill string and the expandable bit are pulled axially upwards allowing the arms to contact a lower end of the casing or another obstruction. As the drill string and the expandable bit continue to be pulled upward, an axial force is created on the release assembly. At a predetermined force, the threaded connection between the hydraulic cylinder and the blade pivot housing fails, thereby activating the release assembly. At this point, the blade pivot housing is allowed to move axially downward pushing the arms over the head and into the collapsed position. In this manner, the expandable bit moves to the closed position allowing it to 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.