Hybrid roller-mill bit and hybrid roller-drag bit

Abstract

A roller-mill bit for use in a wellbore includes: a body having a coupling formed at an upper end thereof and a plurality of lower legs; a plurality of roller disks, each roller disk secured to a bearing shaft of a respective leg for rotation relative thereto; a row of crushers mounted around each roller disk; and a fixed mill mounted to the bearing shafts and comprising a pad for each roller disk. Each pad is dressed with a cermet material.

1 . A roller-mill bit for use in a wellbore, comprising:
 a body having a coupling formed at an upper end thereof and a plurality of lower legs;   a plurality of roller disks, each roller disk secured to a bearing shaft of a respective leg for rotation relative thereto;   a row of crushers mounted around each roller disk; and   a fixed mill mounted to the bearing shafts and comprising a pad for each roller disk,   wherein each pad is dressed with a cermet material.   
     
     
         2 . The roller-mill bit of  claim 1 , wherein:
 the roller disks, crushers, and fixed mill form a lower cutting face of the roller-mill bit, and   the roller disks and crushers are located at an outer portion of the cutting face and the fixed mill is located at an inner portion of the cutting face.   
     
     
         3 . The roller-mill bit of  claim 2 , wherein:
 each leg further has a shirttail, and   each bearing shaft extends from a respective shirttail in a radially inclined direction toward a center of the roller-mill bit.   
     
     
         4 . The roller-mill bit of  claim 1 , wherein:
 each mill pad has a round base and a plurality of side faces converging toward a truncated apex,   at least one of the side faces of each mill pad is a mounting face, and   the mill pads are attached together at the mounting faces.   
     
     
         5 . The roller-mill bit of  claim 4 , further comprising:
 a set of roller bearings disposed between each bearing shaft and the respective roller disk; and   a thrust washer disposed between each roller disk and the respective base.   
     
     
         6 . The roller-mill bit of  claim 5 , wherein:
 each leg further has a shirttail and a ported boss,   a junk slot is formed between the shirttails of each adjacent leg, and   each ported boss is located in a respective junk slot.   
     
     
         7 . The roller-mill bit of  claim 6 , wherein the roller bearings and thrust washers are configured to be lubricated by fluid discharged from the ported bosses. 
     
     
         8 . The roller-mill bit of  claim 5 , wherein each leg has a lubricant reservoir formed therein and a lubricant passage extending from the reservoir to the respective roller bearing set. 
     
     
         9 . The roller-mill bit of  claim 4 , wherein:
 each mill pad has a receptacle formed therein and extending from the base, and   an end of a respective bearing shaft is received in the receptacle, thereby mounting the mill pads to the body.   
     
     
         10 . The roller-mill bit of  claim 9 , wherein:
 each leg further has a shirttail, and   each roller disk is secured to the respective leg by entrapment between the base of the respective mill pad and the respective shirttail.   
     
     
         11 . The roller-mill bit of  claim 9 , wherein each roller disk has a taper formed at a periphery of an inner face thereof and each base has a complementary lip formed at a periphery thereof. 
     
     
         12 . The roller-mill bit of  claim 1 , wherein the roller-mill bit comprises three legs and three roller disks. 
     
     
         13 . The roller-mill bit of  claim 1 , wherein the body further has a dome formed between the legs, a bore formed through the coupling and extending to a plenum formed adjacent to the dome, and a passage formed through the dome for each roller disk. 
     
     
         14 . The roller-mill bit of  claim 1 , wherein the cermet material is a plurality of cutter blocks brazed to the pad. 
     
     
         15 . The roller-mill bit of  claim 14 , wherein the cutter blocks are brazed into grooves formed in the pad at a desired orientation. 
     
     
         16 . The roller-mill bit of  claim 14 , wherein:
 each cutter block has a pair of opposite rectangular sides and four profiled sides connecting the rectangular sides,   the profiled sides each have rectangular end portions located adjacent to the respective rectangular sides and profiled mid portions connecting the respective end portions, and   each rectangular side has a raised peripheral portion and a recessed interior portion.   
     
     
         17 . A method of drilling out a plug using the roller-mill bit of  claim 1 ,
 assembling the roller-mill bit as part of a mill string;   deploying the mill string into a casing or liner string set in the wellbore to the plug set in the casing or liner string; and   injecting milling fluid through the mill string, rotating the roller-mill bit, and engaging the roller-mill bit with the plug, thereby drilling out the plug.   
     
     
         18 . A roller-drill bit for drilling a wellbore, comprising:
 a body having a coupling formed at an upper end thereof and a plurality of lower legs;   a plurality of roller disks, each disk secured to a bearing shaft of a respective leg for rotation relative thereto;   a row of crushers mounted around each roller disk; and   a fixed cutting structure mounted to the bearing shafts and including:
 a center hub; 
 a blade for each roller disk, and 
 plurality of shear cutters mounted to each blade. 
   
     
     
         19 . The roller-drill bit of  claim 18 , wherein the fixed cutting structure further has a plurality of shear cutters embedded in the hub. 
     
     
         20 . The roller-drill bit of  claim 18 , wherein:
 each leg further has a shirttail,   the roller-drill bit further comprises a threaded fastener for each roller disk and blade,   each shirttail and bearing shaft has a bore formed therein receiving a shaft of the respective threaded fastener therethrough,   each shirttail has an opening adjacent to the respective bore receiving a head of the respective threaded fastener, and   each blade has a threaded socket formed therein and receiving an end of the shaft of the respective threaded fastener, thereby mounting the respective blade to the respective bearing shaft and securing each roller disk to the respective leg.   
     
     
         21 . A roller-drill bit for drilling a wellbore, comprising:
 a body having a coupling formed at an upper end thereof, a plurality of lower legs, a dome formed between the legs, and a bore formed through the coupling and the dome;   a plurality of roller disks, each disk secured to a bearing shaft of a respective leg for rotation relative thereto;   a row of crushers mounted around each roller disk; and   a stem mounted to the dome adjacent to the bore and having a port formed through a wall thereof for each roller disk;   a fixed cap mounted to a lower end of the stem; and   one or more shear cutters embedded in or mounted to the fixed cap.   
     
     
         22 . The roller-drill bit of  claim 21 , wherein:
 the fixed cap has a center hub and a blade for each roller disk,   a cavity is formed between each adjacent roller disk, and   the fixed cap is oriented such that each blade extends into the respective cavity.