Patent Publication Number: US-6668949-B1

Title: Underreamer and method of use

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a national stage filing under 35 U.S.C. §371 of PCT/US00/41431, filed Oct. 21. 2000 which claims the benefit of a provisional U.S. application U.S. Ser. No. 60/160,678, filed Oct. 21. 1999, by applicant. 
    
    
     An underreamer is a device used to enlarge the well bore below the casing. Currently used underreamers are long assemblies having blades or cutters which are moved into the well bore by mechanical means to enlarge the hole. The mechanisms for moving the cutter faces into the well bore have significantly impinged on interior space of the body and consequently restricted the fluid passage from the upper end of the underreamer to the lower end. Currently used underreamers have been long and heavy making them impractical to use with steerable downhole motors to simultaneously drill and underream. 
     An underreamer of the present invention is made up of a tubular upper body, threadedly connectable to a drill string, said tubular upper body having a lower end and an upper end each with a different internal diameter, wherein the inner diameter of the lower end is larger than the inner diameter of the upper end. It has a tubular lower body removably attached to the lower end of the tubular upper body, said tubular lower body having at least three skewed, longitudinal grooves and an interior surface defining a longitudinal bore therethrough and an annular lip within the tubular lower body which permits a flowpath having substantially the same diameter through the entire underreamer. It also provides a piston actuator having a longitudinal annular bore, at least three extensions, each having a slot formed thereon, and upper and lower portions, wherein said upper portion slideably and sealingly engages the interior surface of the lower end and wherein the lower portion slideably and sealingly engages the interior surface of tubular lower body and has a lower surface; at least three pins; at least three cutters, each having an ear formed thereon, wherein each of the cutters is pivotally attached within a corresponding one of said at least three skewed, longitudinal grooves using one of the at least three pins and wherein said ear engages the slot of a corresponding one of said at least three extensions; and at least one resilient member positioned between the lower surface of piston actuator and the annular lip of the tubular lower body, said at least one resilient member resisting downward longitudinal movement of the piston actuator assembly. The longitudinal movement of the piston actuator moves the arms into and out of engagement with the well bore and does not rely upon pins and linkages commonly found in prior art underreamers. 
     The present invention offsets the support mechanism of the cutter surfaces of the underreamer from the central longitudinal axis of the tool so that an unobstructed passageway through the tubular body may be provided. It is an object of the present invention to provide a shortened underreamer for use in all forms of drilling operations, including directional drilling operations and drilling programs using steerable downhole drilling motors to permit directional underreaming of formations. The present invention allows drilling and underreaming to occur in one continuous operation and saves the operator the time and expense of drilling a pilot hole then tripping into and out of the hole or reentering the well to underream the pilot hole. The shortened body length of the present invention also allows steerable underreaming while drilling in an economical package. The present invention also avoids the necessity of costly bicentered bit technologies and the inherent weaknesses of conventional underreamers. The present invention permits the simultaneous use of small and therefore cheaper bit technologies with the underreamer and also permits directional control of the underreamer and bit combination. 
     Most generally, the present invention consists of an apparatus formed from a tubular body having threaded connections at each end, an interior surface forming a longitudinal bore through said tubular body and an annular lip within said tubular body, and a plurality of skewed, longitudinal grooves formed in said body; a piston actuator having a lower surface, a plurality of slotted extensions and a longitudinal flow path through said piston actuator, wherein said piston actuator slideably and sealingly engages the interior surface; a plurality of arms, each of said arms having a pivot and an ear, wherein each of said plurality of arms is pivotally mounted in a corresponding one of said plurality of skewed, longitudinal grooves and wherein said ear is adjacent to said pivot and engages a corresponding one of said plurality of slotted extensions; and a plurality of resilient members, wherein each of said plurality of resilient members has a first end and a second end, is located adjacent to a corresponding one of said plurality of slotted extensions, the first end engages the lower surface of the piston actuator, and the second end engages the annular lip. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a half-sectional view of the underreamer in its closed position. 
     FIG. 2 is a half-sectional view of the underreamer in its open position. 
     FIG. 3 is a cross-sectional end view of the underreamer in its open position. 
     FIG. 4 is a perspective view of the upper sub of the underreamer. 
     FIG. 5 is a perspective view of the piston actuator with the spring and spring extender inserted. 
     FIG. 6 is a perspective view of the piston actuator with the slots for engaging the ear of the cutter blades. 
     FIG. 7 is a perspective view of the top interior view of the underreamer tubular body showing the offset, skewed position of the cutter blade slots. 
     FIG. 8 is a perspective view of the underreamer body showing a cutter extended. 
     FIG. 9 is a perspective view of the cutter blade before assembly with the carbide buttons and showing the pin used to pivotally connect the blade to the underreamer body. 
     FIG. 10 is a perspective view of the lower end of the piston actuator. 
     FIG. 11 is a sectional side view of the underreamer adapted for use as a downhole stabilizer. 
     FIG. 12 is a schematic illustration of the use of the underreamer invention shown being run between a downhole motor and a pilot tricone bit. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 is a half-section view of the underreamer  5  of the present invention showing the cutter blades  40  in the closed position as the underreamer is being tripped into or out of the well bore. The underreamer is provided with threads at  10 ′ and  70 ′ in a manner well known in the art for attachment within a drill string. Threads  10 ′ may be used to attach the underreamer  5  to a downhole motor, a drill collar assembly, or a standard drill pipe assembly in a manner well known to those in drilling industry. Threads  70 ′ may be used to connect the underreamer  5  to drill bits (including specializaed drill bits such as a polycrystalline diamond (PDC) bit) or to drill collars or they may be connected to a bull nose to underream a pilot hole previously drilled. The underreamer  5  is formed with an upper sub  10  providing an annular passageway therethrough and terminating with an enlarged inner diameter  11 . The upper sub  10  is threadably connected to the underreamer lower body  70  by threads  10 ″ in a manner well known to those skilled in the manufacture of downhole tools. A perspective view of the upper sub  10  is shown in FIG.  4 . The enlarged lower interior diameter  11  of the upper sub  10  provides a slick bore which provides for slideable engagement of an integral piston actuator  20 , which extends into underreamer lower body  70 . The assembly  20  provides grooves for dynamic seals  21  and  22  to permit hydraulic pressure to be maintained through the underreamer to the drill bit, for example, as the piston actuator  20  moves in the slick bore of body  70 . Piston actuator  20  is a cooperative assembly which is moved in response to increased mud pump pressure down the annulus of the underreamer tubular body  5 . A resilient member comprising a spring extender  60 ′ and spring  60 , which are engaged between the body  70  and the lower surface of the piston actuator  20 , resist downward movement of the piston actuator  20 . 
     The underreamer  5  is actuated by differential pressure against the upper surface of piston actuator  20  that moves the piston down against the resilient member extender  60 ′ and resilient member  60  which seat against the annular lip or shoulder  71  on the interior surface of the underreamer tubular body  70 . FIG. 5 is a perspective view of the piston actuator  20  with the resilient member  60  and resilient member extender  60 ′ shown. The lower end of piston actuator  20  provides extensions having slots  51  machined therein. The piston actuator lower surface also provides a profiled surface  31  designed to mate and lock with the cooperating surface  41  on the cutter  40 . FIG. 6 provides a perspective view of the portion of the piston actuator  20  with the slots  51  and surface  31  as described. The extensions or arms of piston actuator  20  are disposed in the skewed cutter grooves provided by the underreamer body  70 . FIG. 7 shows a top view of the underreamer body  70  with the skewed exterior grooves that accept the extensions of piston actuator  20  at oblique angles to the central axis of the underreamer body, thereby permitting an unrestricted fluid passageway through the annulus of the tool. FIG. 7 also shows the holes  42 ′ drilled in the underreamer body  70  to accept the pins  42  that rotatably support the cutters  40 . 
     As is shown in FIG. 1, cutter  40  provides at its upper end an ear  50  that fits within the slot  51  of the piston actuator  20 . The cutter  40  is connected to the underreamer body  70  by pin  42  that pivots the cutter  40  when the piston actuator  20  is moved longitudinally against the ear  50 . This obviates the need for multiple pin and linkage connections found in many prior art underreamer devices. FIG. 9 is a perspective view which shows the cutter  40  and the ear  50  and specific profile of the cutter  41  which mates with the profile  31  of the piston actuator  20  as shown in FIG.  1 . As the piston actuator  20  moves longitudinally in response to hydraulic pressure acting against the piston face  11 ′, the cutter  40  is moved from its closed position (as shown in FIG. 1) into engagement with the well bore (shown in FIG. 2, and in FIG. 3 as WB) for underreaming or stabilizing. The lower surface  31  of the piston actuator  20  mates with the upper surface  41  of the cutter to lock said cutter  40  in its extended position for underreaming. As may be more fully appreciated from FIGS. 1 and 2, port and jetting arrangement  80  provide fluid communication from the interior of the underreamer body  70  to the area adjacent the cutting surface to carry cuttings away from the cutters  40  and to prevent balling up of material in loose or unconsolidated formations. The manner of making and installing said ports and jets are well known in the industry and are only schematically shown in the drawings. 
     As may be more fully appreciated in FIG. 2 once differential pressure across upper piston surface  11 ′ has overcome the resistance of the resilient member  60 , to move piston actuator  20  into engagement with cutter ear  50  and thus cooperatively moved the cutter  40  out into engagement with the wellbore WB (see FIG.  3 ), underreaming or stabilization may be commenced. FIG. 8 is a perspective view that shows the cutter  40  (without carbide buttons or other cutting surfacing) in its extended position. The pivoting action of the longitudinal movement of the piston actuator  20  which engages the ear  50  on the cutter  40  which pivots about the pin  42  shown in the views from FIG.  1  and FIG.  2 . The underreamer lower body  70  is also provided with ports and jets  80  for directing fluid into the annulus of the well bore to carry cuttings (not shown) from the well bore up. Resilient member  60  and resilient member extender  60 ′ return the piston actuator  20  to the closed position when differential pressure is removed thereby closing the arms so the underreamer can be moved into and out of position for its intended use. Cutters  40  as shown in FIG. 2 are preferably provided with tungsten carbide inserts  90  in the manner more fully disclosed in applicant&#39;s prior patent, U.S. Pat. No. 5,035,293, which is incorporated herein by reference. Other forms of cutters, cutting elements and hardfacing may be substituted in manner well known to the drilling industry without departing from the scope of this invention, such as without limitation, polycrystalline diamond cutters, thermostable diamond composites, and sintered coatings of all kinds. 
     FIG. 3 is a cross-sectional view of the extended cutters  40  showing schematically the engagement of the cutters  40  with the well bore WB. As previously noted, the cutters  40  are rotatably pinned to underreamer body  70  by pins  42 . Pins  42  are held in the underreamer body  70  by cap head screws  43  that are mounted in a groove or slot machined and counterbored in the underreamer body  70  to provide an engagement surface. Each pin  42  is countersunk and tapped (not shown) to permit the easy removal of the pins  42 . The skewed orientation of the pivot pins  42  in the underreamer body  70  allows an unrestricted flow path through the inner passage of the underreamer  5  and permits the maintenance of adequate working pressure below the underreamer such as at the drill bit (not shown). The orientation of the cutters  40  within the body  70  also permit the cutters  40  to engage the surface of the well bore WB at an oblique angle, thus permitting more precise cutting and evacuation of the cuttings from the well bore. This centering action of the cutters  40  provides clean and straight underreamed sections. 
     Prior art underreamers were not sufficiently sturdy to act as stabilizers to maintain downhole assemblies in the central portion of the well bore. The present invention has sufficient strength and stability to act as a stabilizer. FIG. 11 shows the present invention with hardfacing  45 ′ on the outer surface of the blade  45  which is mounted on the underreamer body  70  in the same manner and is functionally activated in the same manner as the underreamer  5  described herein. 
     The underreamer  5  of the present invention is short and may be placed immediately adjacent a drill bit, for example, a polycrystalline diamond (PDC) bit, for example, for drilling directional or horizontal holes. The length of the underreamer allows its use between a PDC bit and a downhole drilling motor. This permits the drilling and underreaming to occur in one trip into the hole without the need to drill a pilot hole, then remove the drilling assembly before using the underreamer. 
     With the present invention, a downhole motor may be connected to the underreamer and be effectively controlled because of the shortened length of the underreamer. This relative shortness permits the operator to steer the drill bit and underreamer to the desired location. By changing out the upper sub  10  of the underreamer  5 , a normal fishing neck may also be placed on the underreamer  5  allowing its using in normal or conventional underreaming programs. When used to steerably drill a hole to a given deviation, the present invention is connected to the drill string between a drill bit and a steerable downhole motor. Steering measurement devices such as MWD, steering tools, and the like are run above the motor, with drill collars and drill pipe to the surface in a manner well known to those skilled in the art. The drilling assembly is lowered into the hole to the appropriate depth. Mud pumps are engaged to pump fluid through the drill string. As the flow is increased, a pressure drop occurs between the inside of the drill string and the outside of the drill string. The pressure drop and flow cause the motor to rotate the underreamer  5  and drill bit. As the flow continues to increase, the motor turns faster and the pressure drop increases sufficiently to open the blades or cutters  40  on the underreamer  5 . The drill string is lowered thereby engaging the bit and underreamer blades or cutters  40  with the formation to be cut and removed. The hole is steered in the desired direction by changing the orientation of the drill string while monitoring the steering devices to make sure the hole is guided on its pre-determined path. Methods of steering and guidance are well known to those skilled in the art. Upon reaching the target, the mud pumps are disengaged reducing flow to zero and causing the pressure to drop to zero. When this occurs, the downhole motor stops rotating and the resilient members  60  retract the underreamer cutters  40  to the closed position. The assembly is then removed from the hole. 
     FIG. 12 is a schematic representation of the underreamer  5  described herein with its cutters  40  extended and connected between the downhole motor  100  and a tricone bit  110  in a configuration that permit continuous drilling and underreaming. As noted previously, because of the shortened length of the present underreamer  5  compared to similar devices, the tricone bit  110  in FIG. 12, could be replaced with a PDC bit. 
     The present invention may also be used to simultaneously drill and underream without a downhole motor. This method is used when a straight hole is desired instead of a directional hole. The underreamer  5  is installed in the drill string above the drill bit. The drill bit may be installed directly to the underreamer  5 , or drill collars may be installed between the bit and the underreamer  5 . The drilling assembly is lowered into the hole to the desired depth. The drill string is then rotated by the rotary table or top drive; again, as is well known in the industry. After rotation is established, the mud pumps are engaged creating flow and pressure drop. As the pressure drop increases, the blades or cutters  40  of the underreamer  5  open to engage the formation. The drill string is lowered thereby engaging the formation to be removed. Upon reaching the desired depth, the pumps are disengaged and rotation is stopped. The blades retract as above and the drilling assembly is removed from the hole. 
     Another use for the present invention is to underream a previously drilled hole to a larger diameter. A drilling assembly is made up as previously described, except that a bull nose or bit may be used below the underreamer  5  to cause the underreamer  5  to follow the previously drilled hole. The operation would proceed as previously described. The present invention may also be used to stabilize a hole that is being drilled and underreamed simultaneously. When used in this fashion, the present invention is fitted with stabilizer blades  45 , with hardfacing  45 ′, as shown in FIG.  11  and is run above the underreamer  5  and drill bit. The preferred location for the stabilizer/underreamer  5  (when used for a stabilizer) would be between 30 to 90 feet above the underreamer. The stabilizer/underreamer  5  (as shown in FIG. 11) above the underreamer would help maintain a straighter hole when drilling and underreaming simultaneously. Operation is the same as previously described in normal drilling operations. The blades  45  of the underreamer used as a stabilizer engaged the well bore when a differential pressure is applied, thereby preventing whipping and “walking off” of the drill string as the drilling proceeds. When the hole reaches the desired depth, the pumps are disengaged and the blades retract permitting removal of the drill string from the well bore. 
     The size, flexibility of makeup and strength of the present underreamer allow it to be used in a number of drilling applications. Other uses of the present invention may be readily appreciated from a review of the drawings and description contained herein.