Patent Publication Number: US-8113301-B2

Title: Jetted underreamer assembly

Description:
FIELD OF THE INVENTION 
     This invention relates in general to earth boring tools, and in particular to an underreamer located above a drill bit that has ports for diverting to the cutters on the underreamer arms some of the drilling fluid being pumped down the drill string. 
     BACKGROUND OF THE INVENTION 
     Underreamers are employed in well drilling operations to enlarge a pilot hole. In casing drilling, the drill string is made up of the casing that will be eventually cemented in the well. If the drill bit is retrievable, it will be part of a bottom hole assembly that latches to a collar or profile sub located near the bottom of the string of casing. The bottom hole assembly extends below the string of casing, and the drill bit is on its lower end for drilling a pilot hole. The underreamer is located above the drill bit for enlarging the pilot hole to an outer diameter greater than the outer diameter of the string of casing. 
     The underreamer has arms that are pivotally mounted to the body of the underreamer for moving between retracted and extended positions. Cutters, typically polycrystalline diamond disks, are mounted to the leading face of each arm. One type of underreamer has an actuator mandrel carried in its longitudinal passage, the actuator mandrel being axially movable from an upstream position to a downstream position in response to drilling fluid being pumped down the drill string. The actuator mandrel is cooperatively engaged with the arms for moving the arms to an extended position when the actuator mandrel moves to the downstream position. 
     The string of casing is rotated by a casing gripper and a top drive of the drilling rig. The bottom hole assembly may include a drill motor that rotates the underreamer and the drill bit independently of the casing string. During drilling, drilling fluid is pumped down the casing string, through the bottom hole assembly and out nozzles of the drill bit. The drilling fluid flows back up the borehole past the underreamer and up the annulus surrounding the string of casing. The drilling fluid removes cuttings and provides lubrication and cooling of the drill bit and underreamer. Nevertheless, in some formations, the cutters on the underreamers arms can become clogged with cuttings and operate at elevated temperatures. Elevated temperatures may be detrimental to the performance and the resistance to abrasion. 
     SUMMARY OF THE INVENTION 
     In this invention, the underreamer has an actuator mandrel carried in its longitudinal passage, the actuator mandrel being axially movable from an upstream position to a downstream position in response to drilling fluid being pumped down the drill string. The actuator mandrel is cooperatively engaged with the arms for moving the arms to an extended position when the actuator mandrel moves to the downstream position. 
     A body port for each arm extends through the sidewall of the underreamer body, each body port being adjacent the face of one of the arms when the arms are in the extended position. Mandrel ports extend through the sidewall of the mandrel. The mandrel ports are spaced above the body ports while the mandrel is in the upstream position. The mandrel ports align with the body ports when the mandrel is in the downstream position. Preferably an abrasion resistant nozzle forms or is mounted in each of the mandrel ports. 
    
    
     
       BRIEF DESCRIPTIONS AND DRAWINGS 
         FIG. 1  is a schematic sectional view illustrating a casing drilling string and bottom hole assembly constructed in accordance with this invention. 
         FIG. 2  is enlarged sectional view of the underreamer of the bottom hole assembly of  FIG. 1 . 
         FIG. 3  is a further enlarged view of a portion of the underreamer of  FIG. 2 , showing an arm in the extended position. 
         FIG. 4  is a view of the underreamer similar to  FIG. 3 , but showing the arm in a retracted position. 
         FIG. 5  is a sectional view of the underreamer of  FIG. 2 , taken along the line  5 - 5  of  FIG. 4 . 
         FIG. 6  is a sectional view of the underreamer of  FIG. 2 , taken along the line  6 - 6  of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
     Referring to  FIG. 1 , a top drive  11  of a drilling rig is schematically shown. Top drive  11  moves upward and downward in a derrick (not shown) and comprises a rotary power source having a quill  13  that rotates. A casing gripper  15  is attached to quill  13  for rotation with it. Casing gripper  15  has gripping members that engage either the inner diameter as shown or the outer diameter of conventional casing  17 . Casing string  17  is shown extending from casing gripper  15  through a rig floor  19  into a borehole  21 . 
     A bottom hole assembly  22  is releasably secured to casing string  17  near its lower end. Bottom hole assembly  22  includes a drill lock assembly (“DLA”)  23 , which is shown attached to a tubular collar or profile sub  25  secured into a lower end portion of casing string  17 . In this example, DLA  23  has a tubular housing  27 . Spring-biased stop dogs  29  extend out from housing  27  and land on an upward-facing shoulder  31  formed in profile sub  25 . DLA  23  also has a set of torque keys  33  for transmitting torque between profile sub  25  and DLA  23 . Torque keys  33  are also biased outward by springs in this embodiment and engage mating longitudinal slots in profile sub  25 . In this embodiment, DLA  23  also has a set of axial lock members  35 . Lock members  35  engage mating recesses in profile sub  25  to prevent upward movement of DLA  23  relative to profile sub  25 . 
     DLA  23  has an upper seal  37  on its exterior arranged for preventing the upward flow of fluid from below. Upper seal  37  may be a downward facing cup seal. DLA  23  may also have one or more lower seals  39  (two shown) for preventing drilling fluid pumped down from above from flowing around the exterior of DLA  23 . Lower seals  39  may also be cup seals but face upward rather than downward. Seals other than cup seals may be employed for seals  37 ,  39 . 
     Bottom hole assembly  22  has a drill bit  43  at its lower end. Drill bit  43  may be any conventional drag blade type or a rolling cone type. An underreamer  45  is located in bottom hole assembly  22  above drill bit  43  and below the lower end of casing string  17 . Bottom hole assembly  22  may also include a drill motor, logging tools, and steering equipment. 
     Referring to  FIG. 2 , underreamer  45  has a tubular body  47  that is made up of several components in this example. Body  47  has an upper threaded end  49  and a lower threaded end  51 . Upper threaded end  49  attaches to other structure in bottom hole assembly  22 , and lower threaded end  51  attaches to drill bit  43 . A longitudinal passage  53  extends through body  47  for transmitting drilling fluid pumped from the drilling rig down casing string  17 . Body  47  and passage  53  have a longitudinal axis  54 . 
     Body  49  has a plurality of axially extending slots  55  formed in its sidewall. In this example there are three identical slots  55 , each spaced about 120 degrees apart from the other around the circumference of body  47 , as shown in  FIG. 5 . Each slot  55  extends from longitudinal passage  53  to the exterior of body  47 . An arm  57  is pivotally secured within each slot  55  for movement between a retracted position ( FIG. 4 ) and an extended position ( FIG. 3 ). Arm  57  has a hole in an upper end through which a pivot pin  59  extends. Pivot pin  59  is secured within mating holes of body  47  on opposite sides of slot  55  to enable arm  57  to pivot between the extended position and the retracted position. Arm  55  has a forward-facing face, considering the direction of rotation, containing cutting elements  61 . Preferably cutting elements  61  comprise polycrystalline diamond disks (“PDC”), each having a flat face that faces into the direction of rotation. This example shows three cutting elements  61  on each arm  57 , but the number could differ. 
     An actuator mandrel  63  is carried within passage  53 . Mandrel  63  has a mandrel passage  65  extending through it that is co-axial with passage  53 . Preferably, a liner  67  is located within at least an upper portion of passage  65 . Liner  67  is formed of a hard, more wear resistant material than mandrel  63 . Mandrel  63  is typically formed of steel, while liner  67  may be formed of tungsten carbide, for example. An annular piston  69  is secured to the upper end of mandrel  63 . Piston  69  has seals  71  on its exterior that seal and slidingly engage a cylindrical portion of passage  53 . Mandrel  63  also has seals  73  on its lower end that seal and slidingly engage a smaller diameter portion of passage  53 . Piston  69  is located above slots  55 , and seals  73  are located below slots  55 . 
     Mandrel  63  has a set of rack teeth  75  formed on its exterior adjacent arms  57 . Rack teeth  75  extend in a straight line axially along mandrel  63 . Each arm  57  has an array of gear teeth  77  formed in a partially circular array that mate with rack teeth  75 . Pumping drilling fluid downward through passage  53  creates a pressure drop within mandrel passage  65  that causes mandrel  63  to move downward to the downstream position shown in  FIG. 2 , thereby pivoting arms  57  to the extended position. In the extended position, arms  57  will circumscribe an outer diameter that is greater than the outer diameter of casing string  17  ( FIG. 1 ). When the drilling fluid pressure ceases and the operator pulls upward, arms  57  will move back to the retracted position to enable underreamer  45  to be pulled upward into the lower end of casing  17 . Piston  69  moves back to the upstream position shown in  FIG. 4 . 
     The annular space surrounding mandrel  63  between piston seal  71  and mandrel seal  73  is not a closed chamber rather, rather it has a vent port  79  to allow fluid below piston  69  to be displaced out as piston  69  moves downward. It is not necessary that an exterior portion of mandrel  63  form a tight seal to the inner diameter of body  47  below vent port  79  and above slots  55 . However, the minimum clearance between mandrel  63  and the interior of body  47  just above arms  57  is quite small. 
     A nozzle  81  may be located near lower threaded end  51  within passage  53 . Nozzle  81  results in a pressure drop to assist in the movement of piston  69  to the lower position. After passing through nozzle  81 , the drilling fluid will pass through nozzles of drill bit  43  ( FIG. 1 ). 
     Referring to  FIGS. 3 and 4 , a body port  83  extends through the sidewall of underreamer body  47  for each of arms  57 . Body port  83  has its inlet in communication with passage  53  and an outlet at the exterior of body  47 . Each body port  83  is preferably inclined downward along longitudinal axes  54  of body  47 , with the inlet located above the outlet. The amount of inclination may vary and, in this example, is about 30 degrees relative to a plane perpendicular to longitudinal axis  54 . 
     A mandrel port  85  extends through the sidewall of mandrel  63  for registering with each body port  83  while mandrel  63  is in the downstream position shown in  FIG. 3 . Each mandrel port  85  is inclined relative to longitudinal axis  54  the same amount as each body port  83 . If a liner  67  is employed, holes  87  will be formed through liner  67  for aligning with and serving as the inlets of mandrel ports  85 . Preferably a nozzle  89  of hard, wear resistant material such as tungsten carbide is secured in mandrel port  85 . Nozzle  89  is located at the inlet end of mandrel port  85  in this example. If mandrel  63  has a fairly thin wall construction, nozzle  89  may extend from the inlet to the outlet of mandrel port  85 . In that instance, the passage through nozzle  89  becomes the mandrel port  85 . The outlet of each mandrel port  85  will register with the inlet of one of the body ports  83  while mandrel  63  is in the downstream position as shown in  FIG. 3 . When mandrel  63  is in the upstream position shown in  FIG. 4 , the outlet of each mandrel port  85  will be spaced axially above the inlets of body ports  83 . Optionally, there are no seals between the outlets of mandrel ports  85  and the inlets of body ports  83 . Because of the internal configuration of nozzle  89 , it will cause convergence of the flow stream from the mandrel passage  65  into body port  83  without significant leakage between mandrel  63  and the interior of body  47 . 
     Referring to  FIG. 3 , a center line  93  of ports  83  and  85  when aligned, will pass across the flat face of the outermost cutting element  61 , and will be slightly upstream from cutting elements  61  located inward of the outermost cutting element  61 . However, the jetted spray diverges from port  83  so that some of it will sweep across the other cutting elements  61 . The outermost cutting element  61  is typically the hottest during operation because it travels the greatest circumferential distance. Aligning centerline  93  with the outermost cutting element  61  assures that cooling fluid and lubrication will be provided. The alignment of the center line  93  with the cutting elements  61  can be varied. 
     Referring to  FIG. 6 , in this example, nozzles  89  do not point along radial lines from longitudinal axis  54  of mandrel passage  65 ; rather centerline  93  of each nozzle  89  is at an angle to the radial line  95  that passes through the same nozzle  89 . Centerline  93  thus does not intersect longitudinal axis  54 . Considering the direction of rotation to be in indicated by the arrow in  FIG. 6 , each centerline  93  lags a radial line  95  that passes through the same nozzle  89 . Each arm  57  does have a center point that would be on a radial line  95 . However, the face of each arm  57  is not on a radial line  95  from axis  54 , rather it is rotationally forward of the radial line. Nozzles  89  are oriented so that each centerline  93  is substantially parallel and spaced a short distance forward from the face of each arm  57 . This orientation causes the jet spray to sweep across the faces of cutting elements  61  ( FIG. 3 ). 
     In operation and referring to  FIG. 1 , bottom hole assembly  22  is secured to profile sub  25  for rotational and axial movement by dogs  29  and torque keys  33 . Casing string  17  is lowered to the bottom of borehole  21 . The operator operates top drive  11  to rotate casing string  17  and pumps drilling fluid down casing string  17 , which flows into the upper end of bottom hole assembly  22 . The drilling fluid pressure pushes piston  69  ( FIG. 2 ) downward, moving arms  57  to the extended position. Some of the drilling fluid is jetted out ports  85  and  83  and discharges across cutting elements  61  of each arm  57 . The remaining drilling fluid flows out nozzles of drill bit  43  and back up around arms  57  and casing string  17  to the surface. The drilling fluid being jetted out ports  85  and  83  provides cooling, lubrication, and cleaning for cutting elements  61  of underreamer arms  57 . 
     While the invention has been shown in only one of its forms, it should be apparent to those skilled in the art, that it is not so limited but is susceptible to various changes without departing from the scope of the invention.