Abstract:
The invention combines a mud motor, a drill bit, a transmission, an underreamer and a torque tube to simultaneously drill a well by rotating the drill bit in one direction and the underreamer in the opposite direction to balance the torque supplied to the bit and the underreamer.

Description:
FIELD OF THE INVENTION 
     This invention relates to an improved method of and apparatus for drilling oil and gas wells using a mud motor. 
     BACKGROUND OF THE INVENTION 
     When drilling with a mud motor reactive torque is a problem. High drilling rates and high weight on the bit causes the mud motor to stall, the bit to stop, and the drill string to rotate in the opposite direction due to torque build up in the drill string, and mud motor failure all caused by reactive torque, and torsional loads on the drill string. Therefore, it is an object of this invention to provide apparatus for and method of drilling that will balance reactive torque by drilling and underreaming simultaneously with a bit rotating in one direction and an underreamer rotating in an opposite direction. 
     SUMMARY OF THE INVENTION 
     Specifically, the apparatus of this invention includes a drill bit, a fluid powered motor connected to the bit for rotating the bit, an underreamer above the bit to increase the diameter of the well bore, and a gear box positioned between the bit and the underreamer for transmitting the reactive torque of the fluid powered motor to the underreamer to rotate the underreamer in a direction opposite that of the bit so that the torque rotating the bit is substantially the same as the torque rotating the underreamer to therefore create a balanced torque drilling system. 
     A hollow mandrel or torque tube  22  extends along the central axis of the apparatus from just above fluid powered motor  18  to just below top connection  25 . Spline connection  23  between the upper end of the torque tube and bottom end  51  of connector  25  hold the torque tube from rotating around the central axis of the tool. The lower end of the torque tube is prevented from rotating by pins  36   a  and  36   c  that extend through pinions  28   a  and  28   c,  respectively, and the wall of housing  12 . The torque tube, be it titanium and/or composite, serves to absorb shock torque especially from formation breaks, but also to permit rotating the drill string with the rotary table while drilling with a mud motor. This allows the tool to build angle with stabilizers when desired. 
     Therefore, it is an object and feature of this invention to provide a down hole drilling assembly to minimize or balance the reactive torque of a mud motor rotating a bit in one direction with an underreamer rotating in the opposite direction. This is accomplished by a gear box located between the mud motor and the underreamer. Specifically, the bit is turned by a mud motor, the upper end of the motor drives a reversing gear box that turns the underreamer in a direction opposite that of the bit. A torque tube or mandrel extends along the longitudinal central axis of the tool. The lower end of the torque tube is connected to the gearbox and to the gear box housing to hold lower housing section  12  in position to enclose and support the gear box and the mud motor. The torque tube also serves to supply drilling fluid under pressure to the mud motor through openings  26   a,    26   b  and  26   c  in spacer  20  to rotate the bit connected to the output shaft of the mud motor. The torque tube is an axis guide for the underreamer to rotate about. Balancing the rotating members such as bit, stabilizer and underreamer is accomplished by grooved circular races  82  and  86  that contain a portion of high density small pellets in an oil/TEFLON fluid median. The pellets do not fill the grooves so that centrifugal force produced by the rotating tool causes balancing and increases mud motor life by decreasing bearing failure. FIG. 4 is an enlarged cross section view of one of the balancing grooves. 
     These and other objects, advantages, and features of this invention will be apparent to those skilled in the art from this specification including the attached drawings, and appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The preferred embodiment of the invention will be described in detail below with reference to the following drawings: 
     FIG. 1 is a view, in elevation of the drilling assembly of this invention in the process of drilling a well bore with a conventional bit and simultaneously underreaming the well bore drilled by the bit to a larger diameter by an underreamer spaced above the bit. 
     FIG. 2A and 2B are sectional views of the portion of the drilling assembly of this invention from the drill bit to the drill pipe connected to the upper end of the drilling assembly. 
     FIG. 3 is a sectional view taken along line  3 — 3  of FIG.  2 A. 
     FIG. 3A is a detail elevation section view of the gear box portion of the drilling assembly taken along line  3 A— 3 A of FIG.  3 . 
     FIG. 4 is a sectional view taken along line  4 — 4  of FIG. 2A of balancing ring  80 . The balancing ring comprises annular groove  82  with a semicircular bottom. The groove is filled with balls of high density metal, such as lead, tungsten carbide or depleted uranium. Preferably, the balls do not completely fill the groove so they can move to a position in the groove in response to the centrifugal force on the balls produced by the rotation of the tool and to provide a balancing force to the rotating members. 
     FIG. 5 is a sectional view taken along line  5 — 5  of FIG.  2 A. 
     FIG. 6 is a view, similar to FIG. 1 showing in section the components of the underreamer that move the cutting arms of the underreamer into position to enlarge the diameter of well bore  19  as the well bore is being drilled. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIG. 1 the drilling assembly of this invention is shown in elevation. At the lower end, drill bit  10  is in contact with the bottom of well bore  19  and is being rotated to the right relative to housing  12  by the apparatus in housings  12  and  14  that will be described in detail below. 
     Specifically, FIGS. 2A and 2B are sectional views of the apparatus of this invention for rotating the drill bit. Drill bit  10 , that is in engagement with the bottom of the well bore, is connected by sub  14  to the end of output shaft  16  of pump  12 , which is preferably a Robbins &amp; Myers Moynog®-brand pump, and referred to hereinafter as “Moyno pump”. In FIG. 2A, the upper end of Moyno pump  12  is shown connected to flow diverter  20 . Above flow diverter  20 , mandrel  22  extends from tool joint box  25  to just above flow diverter  20  and ties all the various parts of this tool together. It is a hollow tube and the upper end is positioned in line with the opening in drill pipe pin  24  as shown in FIG.  2 A. Fluid pumped down the drill pipe will flow through hollow central mandrel  22  and ports  26   a,    26   b  and  26   c  in flow diverter  20  positioned at the bottom of the tube. Flow diverter  20  is an integral part of shaft  16  of Moyno pump  12 . Central passage  26   b  is located in the impeller of Moyno pump  12  and fluid flows through opening  26   b  to the top of resilient body  18  of Moyno pump  12 . This fluid then provides the power to rotate shaft  16  of the Moyno pump and bit  10  that is attached to the lower end of output shaft  16  of the Moyno pump to drill well bore  19 . 
     Referring now to FIG.  3  and FIG. 3A, which are enlarged sectional views of the gear box that is located above the Moyno pump and is connected to mandrel  22 . As shown in FIG. 3 there are four equally spaced pinions,  28   a,    28   b,    28   c  and  28 d in the gear train which engage two longitudinally spaced, annular bevel ring gears  29   a  and  29   b,  the beveled ring gear teeth of which diverge outwardly. The upper ring gear  29   a  is pinned to an upper spacer  90  with a pin  90   a  and the lower ring gear  29   b  is pinned to lower spacer  20 . The pins connecting the upper and lower ring gears to the spacers hold the ring gears from rotation relative to the spacers and the housing. Pinion  28   a  is not shown in FIG. 3A in order to show the structural arrangement of arms  30   a - 30   d  of anchor spider  30  on which the pinions are mounted. The spider consists of a central tubular section  36   f  with four arms  30   a,    30   b,    30   c,  and  30   d  symmetrically extending radially from the center section. The central section is designated by number  30   f  and the arms are  39   a  through  30   d.  The arms are welded to tubular housing  39  in which they are located, as shown in FIG.  3  and also FIG.  3 A. Pins  36   a  through  36   d  are mounted in the wall of the housing and support pinions  28   a  through  28   d  for rotation as shown in FIG.  3 . 
     FIG. 3A is the vertical section through FIG. 3 taken along line  3 A— 3 A in FIG.  3 . Consequently, the pinion on pin  36   a  is not shown. As explained above, drilling fluid will be pumped down through the center of mandrel  22  and when the fluid reaches the lower end of tube  22  the fluid will exit through large port  26   b  and provide drilling fluid under pressure to the Moyno pump  12  to rotate bit  10  that is connected to the lower end of the apparatus. Portions of the fluid in mandrel  22  will be diverted through smaller outlets  26   a  and  26   c.  As explained above this fluid will flow through opening  26   b  into the Moyno pump to provide the force necessary to rotate motor shaft  16  of the Moyno pump and bit  10 . 
     Torque tube or mandrel  22  has opening  22   a  as shown in FIGS  2 A and C through which drilling fluid being pumped down the drill pipe into the motor will flow and exert a downward force on piston  60  causing the piston to move downwardly against spring  61  so that rachet teeth  62  that engage rachet teeth  63  on cutting arms  64  and  65 , will rotate the cutting arms outwardly to a lateral position relative to the longitudinal axis of the tool rotation of the tool will cause cutting arm  64  and  65  to enlarge the diameter of the hole being drilled by bit  10  as the underreamer is rotated and lowered as shown in FIG.  1 . 
     A significant factor in premature mud motor failures is caused by imbalance and harmonic vibrations, due to the fact that the bit, the stabilizers, and the underreamers get unbalanced due to cuttings getting packed into stabilizer ribs (leading edges) and drilling bit legs. This extra weight is eccentric to the center line of the drilling assembly and that creates an imbalance and vibrations that creates a side thrust load on the mud motor bearings. 
     Circumferential balancing grooves, such as  82  and  86 , on rotating members are filled with a high density median, such as tungsten or depleted uranium in light oil and TEFLON liquid carrier will tend to selfbalance by rotating centrifugal force. The high density median would compensate for the imbalance caused by the extra mass of impacted/compacted formation. These rings could be machined on rotating members (stabilizers, underreamers, bit subs etc.) and filled with the high-density balancing fluid. FIG. 4 is a cross sectional view taken along line  4 — 4  of FIG. 2A of balancing ring  82 . Mandrel  22  is in the center surrounded by a portion of body  82  and the upper end of torque tube  22  and spline connection  23 .