US 3716106 A
A drilling system for rotary drilling. A drilling system for the rotary drilling of well bores utilizing a pair of cooperating subsystems, one subsystem providing for control of the penetration rate or weight of the drill bit, the second subsystem controlling the rotational speed or torque of the drill bit. A drawworks supporting the drill string is cooperatively engaged to a continuously slipping clutch to provide precise control over the vertical motion of the drill string and bit. The rotary drill table providing rotational power to the drill string and bit is cooperatively coupled to a continuously slipping clutch to provide precise control over the rotational motion of the drill string and attached drill bit.
Description (OCR text may contain errors)
United States Patent 91 Peterson [4 1 Feb. 13, 1973 CONSTANTLY SLIPPING CLUTCH CONTROL FOR ROTARY DRILLING  Inventor: Earl A. Peterson, 41 l l Chestnut Ave., Long Beach, Calif.
 Filed: July 30, 1971 211 App]. No; 167,713
Related U.S. Application Data  Continuation-in-part of Ser. No. 810,322, March 25,
 References Cited UNITED STATES PATENTS 9/1957 OLeary ..l73/4 7/1960 Wilson ..254/l87A Primary Examiner-Ernest R. Purser AttorneySpensley, Horn and Lubitz 5 7 1 ABSTRACT A drilling system for rotary drilling. A drilling system for the rotary drilling of well bores utilizing a pair of cooperating subsystems, one subsystem providing for control of the penetration rate or weight of the drill bit, the second subsystem controlling the rotational speed or torque of the drill bit. A drawworks supporting the drill string is cooperatively engaged to a continuously slipping clutch to provide precise control over the vertical motion of the drill string and bit. The rotary drill table providing rotational power to the drill string and bit is cooperatively coupled to a continuously slipping clutch to provide precise control over the rotational motion of the drill string and attached drill bit.
11 Claims, 4 Drawing Figures PATENTEDFEB13 I975 3.716.106
EARL A. PETERSON INVENTOR SPE/VSLEYJ/OR/Vfi LUB/TZ ATTORNEYS PATENTEUFEB 13 I975 3,716,106
SHEET 2 [IF 3 EARL A. PETERSON Fl g. 2 INVENTOR .S'PE/VSLE Y, HOE/V8 LUB/T Z ATTORN EYS CONSTANTLY SLIPPING CLUTCH CONTROL FOR ROTARY DRILLING This is a continuation-in-part of my application Ser. No. 810,322 filed Mar. 25, 1969 and now abandoned.
BACKGROUND OF THE INVENTION 1. Field of the lnvention The present invention drilling system is generally related to the field of well bore drilling apparatus and, l
more particularly, to rotary drilling apparatus.
2. Prior Art With the increasing importance of off-shore and onshore drilling of oil and gas wells, the need to improve the control over such operations has become evident. The problems which are incident to the drilling of well bores have been known for a great deal of time. Since the drill bit must penetrate the earth to a great distance, the weight on the drill bit must be maintained at a predetermined level in spite of the increased weight added by the drill pipe as the drill string becomes longer. Even with the use of drill collars and slip joints, tension in the drill string must be controlled. Conventional systems disclosed by the prior art utilized static hoisting equipment to support the weight of the drill string at the surface. Where the drilling of the well bore is in an off-shore environment, this apparatus is totally unusable to compensate for the vertical displacement of wave motion.
Another device disclosed by the pr-iorart to'seek to control the rate of penetration of the drill string or the bit weight utilizes a fluid coupling to seek to compensate for the added weight of the drill string and wave motion where the well bore is being drilled in an ovvshore environment. The attempt to use a fluid coupling between the power source and the hoisting apparatus leaves substantial problems unresolved. The weight of a drill string can be as high as 400,000 lbs. thereby imposing loads which cannot be suitably supported by the fluid coupling. In addition, wave action can cause inhaul and over-haul action on the fast line of the supporting apparatus which cannot be properly compensated for by a fluid coupling. in addition, this system disclosed by the prior art provides no means for con trolling the rotational speed or torque on the drill string and the-drill bit. This is necessary to prevent damage to the bit or the rotary drill table.
Another device disclosed by the prior art utilizes a single power source coupled to both a hoisting apparatus as well as a rotary drill table through separate power transmission devices. The power sources are coupled to the hoisting mechanism and the rotary drill table through a torque converter. The required torque converter and transmission present severe operational and equipment problems which are totally resolved by the present invention. The drawworks used to support the drill string and the cooperating rotary drill table are each controlled by continuously slipping clutches adapted to provide controlled torque to the respective drawworks and rotary drill table. By appropriate sensors, the drill string can be supported by the controlled torque of a first continuously slipping clutch, the rotational torque of the rotary drill table being controlled by a second continuously slipping clutch. The combination of the two subsystems provide a method for rotary drilling which substantially resolves the problems left unresolved by the apparatus disclosed by the prior art.
SUMMARY OF THE INVENTION The present invention drilling mechanism constitutes a method for rotary drilling and apparatus for implementing same. A drawworks hoist is driven by a continuously slipping clutch to provide controlled torque on the fast line attached thereto. The continuously slipping clutch is operated in an overspeed condition whereby the driving member is rotated at a speed 0 which will permit compensation for the increased weight of the drill string and for wave motion where the present invention is utilized in an off-shore environment. The drill string is supported by the fast line attached to a drum of the hoist. As additional lengths of drill pipe are added to the drill string, the load on the fast line will be increased. In addition, where the well bore being drilled is in the ocean or other body of water subject to wave motion, the tension in the fast line is maintained at a predetermined level to control the penetration rate of or weight upon the drill bit. The driving member of the continuously slipping clutch is appropriate to maintain a controlled tension in the fast line irrespective of whether the drilling vessel is rising or falling with the water level. The control over this weight is extremely important where the drilling of the well bore is in an off-shore environment. The drawworks utilizing the continuously slipping clutch to implement the first subsystem of the present invention drilling mechanism is similar to that described in Applicants U.S. Pat. No. 3,373,972.
The drill string is supported by a kelly disposed through the rotary drill table, a traveling block supporting the kelly on a swivel joint. The fast line from the drawworks is carried over a crown block at the top of the drilling derrick, the traveling block being supported by the drawworks cable. The rotary drill table is powered through a continuously slipping clutch permitting precise control over the rotation of the rotary drill table and therefore the speed and torque imposed upon the drill bit.
It is therefore an object of the present invention to provide an improvedmethod for rotary drilling of well bores.
It is another object of the present invention to provide an apparatus for rotary drilling which can control the bit weight of the drill string and the torque imposed upon the drilling bit.
It is still another object of the present invention to provide an improved apparatus for rotary drilling utilizing continuously slipping clutches.
It is yet another object of the present invention to provide a method of rotary drilling whereby the penetration rate and rotation of the drill bit can be precisely controlled.
The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objectives and advantages thereof will be better understood from the following description considered in connection with the accompanying drawing in which a presently preferred embodiment of the invention is illustrated by way of example. It is to be expressly understood, however, that the drawing is for the purpose of illustration and description only, and is not intended as a definition of the limits of the invention.
BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a side, elevation view of a drilling platform embodying a supporting drawworks and power source for a rotary drill table in accordance with the present invention.
FIG. 2 is a top plan view of the drawworks hoist of FIG. 1 utilizing a continuously slipping clutch assembly in accordance with the present invention.
FIG. 3 is a side, elevation view, shown in partial cross-section, of a clutch assembly taken through line 33 of FIG. 2.
FIG. 4 is a top plan view of the rotary drill table of FIG. 1 powered in accordance with the present invention.
DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENT An understanding of the cooperative relationship of subsystems of the present invention can be best gained by reference to FIG. 1 wherein a side, elevation view of the drilling derrick and associated equipment is shown, the drilling derrick being generally designated by the reference numeral 10. For the purpose of example, drilling derrick is shown mounted upon drilling barge ll, drilling barge 11 being anchored in an aqueous environment 12 such as the oceamAlthough it is within the scope of the present invention to utilize the present invention method of rotary drilling on on-shore applications, the advantages of the present invention are most fully realized where the apparatus for implementing the present invention is utilized in the offshore drilling of well bores. Barge 11 is shown held in a substantially stationary condition above well bore 13 by anchor lines 14 or other appropriate stabilizing means. Drawworks 15 and a power unit 16 capable of producing controlled tension in the fast line or hoisting cable 17 are mounted upon the deck of barge or other floating structure 11. Hoisting cable 17 is supported by crown block 18 at the top of derrick 10, the traveling end of hoisting cable or fast line 17 carrying traveling block 19 and hook 20. The dead line of hoisting cable 17 is terminated at a stationary point such as on derrick 10, weight sensor 21 being disposed in the dead line for determining the weight imposed upon drill bit 22.
Hook supports swivel joint 23 which is typically supplied with drilling fluid through mud hose 24 connected to a mud pump which is not shown. Kelly joint 25 depends downwardly from swivel joint 23 through a kelly bushing in the center of rotary drill table 26. Drill string 27 is coupled to the lower end of kelly 25 and extends through water 12 into well bore 13. Drill bit 22 is connected to the lower end of drill string 27 for providing the penetration of well bore 13.
Rotary table 26 is powered through shaft 28 by power unit 29, power unit 29 providing means for precisely controlling the rotation or torque imposed upon bit 22. Power unit 29 will be described in greater detail hereinbelow.
As stated, an object of the present invention is to provide means for controlling any combination of penetration rate and bit weight on one hand and rotational speed or torque of bit 22 on the other. In addition, the present invention method of rotary drilling provides means forcontrolling the parameters of rotary drilling as stated along with allowing for motion compensation arising out of wave or tidal action of ocean 12. Referring now to FIG. 2, an understanding of drawworks 15 and power unit 16 can be best gained. Fast line 17 is typically hauled in and hauled out through the power provided by motors and 41. Although the scope of the present invention embodies the use of any number and type of suitable power sources, motors 40 and 41 typically comprise series wound DC motors typically having a power output of 700 horsepower each. The output shaft of motor-40 is coupled to input shaft 42 by way of shaft coupling 43. Shaft coupling 43 is a conventional device used to mechanically connect axially aligned shafts. The output shaft of motor 41 is coupled to input shaft 42 at shaft coupling 44. As stated above, shaft coupling 44 is a conventional coupling device. Shaft couplings 43 and 44 will mechanically couple the torque output of motors 40 and 41 to input shaft 42. The elements of drawworks 15 are supported by a fixed frame, shaft 42 being rotatably mounted or otherwise journeled in suitable bearings 45 and 46.
The rotational power imposed upon input shaft 42 is transmitted to the remainder of drawworks 15 by drive sprockets 47 and '48 concentrically disposed about input shaft 42 substantially adjacent bearings 45 and 46 respectively. Drive sprockets 47 and 48 are typically chain drive sprockets, but they can be any other suitable torque transmitting devices such as pulleys. Drive sprockets 47 and 48 concurrently supply power to jack shaft 49, gear tooth clutch 50 selecting either sprocket 51 or sprocket 52, the power of both motors 40 and 41 being transmitted through the selected sprockets 51 or 52. Although drive sprocket 48 is shown to be substantially equal in size to drive sprocket 47, the number of drive sprockets 48 will typically exceed the number of drive sprockets 47 to provide additional torque transmitting capacity.
Drive sprocket 47 is coupled to driven sprockets 51 by chain 53 and drive sprockets 48 are coupled to driven sprockets 52 by chain 54. Sprockets 51 and 52 are rotatably mounted upon jack shaft 49, each being selectively coupled to shaft 49 by gear tooth clutch 50 which is in itself concentrically disposed upon jack shaft 49 and secured thereto. Although the scope of the present invention is broad enough to implement gear tooth clutch 50 by any suitable power transmission device, gear tooth clutch 50 is preferably a two speed gear tooth clutch transmission. Where gear tooth clutch 50 is a two speed transmission, use of motors 40 and 41 produces four operating modes based upon selected speed and torque output. As will be discussed below, the use of power unit 16 provides an additional operating mode which provides the improved characteristics of the present invention.
One end of shaft 49 is journeled in suitable bearing 55, the end of shaft 49 depending beyond bearing 55 having concentrically mounted thereon sprockets 56 and 57. Sprockets 56 are coupled to sprockets 78 by way of chain drive 79. Sprockets 78 are secured to the housing of high-speed drum clutch 58. Although highspeed drum clutch 58 can be implemented through the use of conventional clutches, high-speed drum clutch S8 is preferably an air-actuated clutch providing for positive engagement between the driving and driven elements thereof. Actuation of high-speed drum clutch 58 is provided by a conventional roto-coupling 59 through which the activating air line for engaging and disengaging high speed drum clutch 58 is directed. When high-speed drum clutch 58 is engaged, the torque output thereof will appear upon shaft 60 thereby being transmitted to drum 61 and fast line 17. Drum 61 is keyed or otherwise secured to shaft 60 in a conventional manner, the manner of securing drum 61 to shaft 60 not being part of the present invention. Shaft 60 is journeled in suitable bearing 62 and 63 of the fixed frame.
Power is transmitted to low-speed drum clutch 64 in a similar manner to that utilized to transmit power to high-speed drum clutch 58. The second end of shaft 49 is journeled in suitable bearing 65 of the fixed frame, the end of drive shaft 49 extending beyond bearings 65 having concentrically secured thereto sprockets 66. Sprockets 66 are coupled to sprockets 67 by'chain drive 68, sprockets 66 being secured to the clutch housing or driving member of low-speed drum clutch 64. Torque transmitted through low-speed drum clutch 64 is supplied to shaft 60, to drum 61 and to fast line 17. Although the scope of the present invention embodies any number of suitable, conventional clutches to implement low-speed drum clutch 64, low-speed drum clutch 64 is preferably implemented through the use of an air actuated, ventilated disc clutch. Control lines for supplying air actuation to low-speed drum clutch 64 is axially disposed through shaft 60 at rotocoupling 69. Drum 61 is equipped with a conventional supplemental braking system referencing the movement of drum 61 to the fixed frame.
Since the drilling ofa well bore typically requires the use of an additional hoist for raising or lowering a variety of devices into the well bore, sandline drum 70 is secured to shaft 71, shaft 71 being journeled in suitable bearing 72 and 73 of the fixed frame. Sprockets 57 axially disposed adjacent sprockets 56 on jack shaft 49 are coupled to sprockets 74 via chain drive 75. Sprockets 74 are concentrically disposed upon and secured to shaft 71. The drilling of a well bore typically requires a number of operations whereby the drill string is pulled out and reinserted for changes of the drill bit. Since the drill string is typically comprised of a series of coupled drill pipes, catheads 76 and 77 are axially disposed at opposite ends of shaft 71, each of catheads 76 and 77 being used for the alternate purpose of the make-up or break-up of the drill string.
As stated, an object of the present invention is to provide means whereby the penetration rate or weight upon'drill bit 22 can be controlled. As shown in FIG. 2, power unit 16 is coupled to drawworks 15 to provide alternate means for providing tension in fast line 17. Sprockets 80 are concentrically disposed upon and secured to shaft 81, shaft 81 being journeled in suitable bearing 82 of the fixed frame. Sprockets 83 are concentrically secured to input shaft 42 adjacent sprockets 47, sprockets 80 being coupled to sprockets 83 via chain drive 84. The driven elements of clutch 85 are coupled to shaft 81, the housing of clutch 85 being secured to sprockets 86. Sprockets 86 are coupled to sprockets 87 via chain drive 88, sprockets 87 being secured to the output shaft of independent power source 89, typically being a DC, series wound motor.
Clutch is one capable of operating in a continuously slipping mode whereby there is a controllable differential speed between the input and output of clutch 85. Sprockets 86 are connected to and impart rotational power to drive ring 90 which is secured to the housing of clutch 85. Sprocket 86 and drive ring 90 are rotatably mounted upon shaft 81. Although it is within the scopeof the present invention to implement clutch 85 by a number of conventional mechanically engaging clutches, clutch 85 is preferably an air actuated, water cooled disc clutch capable of operating in a continuously slipping mode wherein there is a controlled differential speed between the hub and housing and therefore the driven friction disc and driving friction elements of the clutch. in this form of the present invention, actuation and cooling of clutch 85 is accomplished through the use of roto-coupling 91.
An understanding of the manner in which controlled tension may be maintained in fast line 17 can be best gained by reference to FIG. 3 wherein an enlarged cross-sectional, side elevation view of clutch 85 is shown. As stated, it is within the scope of the present invention to implement continuously slipping clutch 85 through the use of torque transmitting clutches having heat dissipation characteristics suitable to permit significant speed differentials between the input and output friction elements of the clutch. It is preferred that an air actuated, liquid cooled disc clutch be used to implement clutch 85. Referring now to FIG. 3, clutch 85 comprises a substantially cylindrical like housing 100, axial surface 101 therefore being secured to longitudinal surface 102 of drive ring 90, housing being secured to drive ring 90 by conventional bolts 103. Shaft 81 is rotatably mounted in suitable bearings 82. Drive ring 90 is comprised of hub 104, an end thereof being radially extended into ring portion 105, ring portion 105 being secured to clutch housing 100. Drive ring 90 is rotatably mounted upon shaft 81, drive ring 90 being journeled on suitable bearings 106. Sprockets 86 are radially secured to a portion of hub 104 of drive ring 90, sprockets 86 as shown in FIG. 3 having two sets of sprocket teeth for receiving chain drive 88 (FIG. 2) Sprockets 86 can be mounted upon hub 104 by any suitable means.
Slidingly adjacent the inner axial surface of housing 100 is friction plate carrier 107, friction plate carrier 107 being adapted to receive driving friction element 108. Friction element 109 is secured to an interior receiving surface of housing 100 adjacent the surface of friction disc 110 and opposite friction element 108. Annularly disposed within driving friction plate carrier 107 and adjacent driving friction element 108 is annu-. lar channel 111. Annularly disposed within housing 100 adjacent friction element 109 is annular channel 112. Annular channels 111 and 112 are adpated to receive sufficient liquid, typically water, for dissipating heat created by the frictional engagement of friction elements 108 and 109 and friction disc 110. Friction disc 110 is securely mounted by spline teeth 113 on clutch hub 114 which in turn is keyed or otherwise secured to shaft 81.
In order to engage clutch 85, air is introduced to expandable element 115 by appropriate fittings through shaft 81 from rote-coupling 91 (not shown). Friction plate carrier 107 is slidably engaged to the interior wall of housing 100 to axiallymove along the axis of shaft 81 through the alternative action of expandable element 115 and return spring 116. Friction plate carrier 107 has no rotational motion with respect to housing 100 while permitting axial movement with respect thereto. Air is introduced for expanding expandable element 115 at air coupling 92 and liquid coolant is introduced at roto-coupling 91 to provide an inlet and outlet for the coolant disposed within annular channels 111 and 112, connections to rote-coupling 91 not shown.
In order for clutch 85 to operate as a continuously slipping clutch, clutch 85 must be fully capable of fully dissipating the heat horsepower generated by the frictional engagement between driving friction elements 108 and 109 and friction disc 110. When the present invention method of rotary drilling operates drawworks to maintain fast line 17 in a controlled tension mode, clutch 85 will be engaged. Drive power is supplied by rotating sprockets 86 which in turn causes a given rotational speed and torque to be applied to housing 100 and friction plate carrier 107. The degree of tension in fast line 17 is dependent upon the magnitude of the frictional engagement between driving friction elements 108 and 109 and driven friction disc 110. Air is introduced into expandable element 115 which in turn will cause friction plate carrier 107 to be slidably moved. Since friction element 109 is substantially stationary, driven friction disc 110 will be frictionally engaged between the opposing surfaces of friction elements 108 and 109. By providing a controlled speed differential between driving friction elements 108 and 109 and friction disc 110, the torque imposed upon shaft 81 will be imparted to shaft 60 (FIG. 2) thereby maintaining a controlled tension in fast line 17. During the controlled tension mode of rotary drilling, high-speed and low-speed drum clutches 58 and 64 respectively will be disengaged.
In order to provide a complete rotary drilling system as stated, FIG. 4 illustrates a portion of rotary drill table 26 and the power thereto as provided by power unit 29. Power unit 29 drives rotary drill table 26 via shaft 28. Shaft 28 is coupled to rotary drill table 26 via a conventional pinion gear (not shown) thereby changing the axis of rotation by 90. Referring now to FIG. 4, rotary drill table 26 has disposed therein a receiving orifice for providing the rotational force in kelly joint 25 (FIG. 1). Shaft 28 through appropriate pinion gears has mounted thereon sprockets 120, shaft 28 being rotatably mounted insuitable bearings 121 of the frame of power unit 29. Sprockets 120 are coupled to'sprockets'122 which are mounted upon shaft 123 journeled in suitable'bearings 124 of the fixed frame of power unit 29, Shaft 123 is coupled to the hub of clutch 125 in the same manner as shaft 81 is coupled to clutch hub 114 in FIG. 3. The clutch housing of clutch 125 is coupled to ring gear 126 upon which is concentrically disposed and secured thereto sprockets 127. Ring gear 126 is rotatably mounted upon shaft 123 by suitable bearings in the manner shown in FIG. 3. Power is delivered to sprockets 123 and chain drive 129 which is mounted upon the output shaft 130 of motor 131. Chain drive 129 transmits power to sprockets 127 and therefore to clutch 125. Although it is within the scope of the present invention to utilize a conventional motor for motor 131, motor 131 is typically implemented through the use of a DC, series wound motor. In the same manner as described with respect to clutch 85, clutch 125 is adapted to be operated in a continuously slipping mode. Clutch 125 is preferably an air actuated, liquid cooled disc clutch wherein air is introduced at air coupling 132, the water inlet and outlet being at rotocoupling 133.
As stated, it is an object of the present invention to provide means for controlling the rotational speed or torque of rotary drill table 26 and therefore the rotational speed and torque at drill bit 22. When there are no means for precisely controlling the rotational speed or torque at drill bit 22, encountering material which is exceptionally hard will cause failure in the power system of the rotary drill table or at the least damage to the pinion gears which couple the power to the rotary drill table. Clutch 125 is capable of providing a predetermined speed differential between the driving I and driven elements of clutch 125, the input speed provided to the driving elements by motor 131 being directly related to the torque output of clutch 125 based upon the frictional engagement of clutch 125. Where the rotational speed ortorque imposed upon drill bit 22 is sensed in a conventional manner, control over the air actuation of clutch 125 can be accomplished to precisely control the torque or speed of drill bit 22. Since the clutch 125 can dissipate the heat horsepower generated by the continuously slipping clutch between the driving and driven elements of the clutch, precise control can be maintained over the pertinent parameters without the inherent time delays, errors and inadequate capacities inherent in the devices disclosed by the prior art. 7
The operation of the total rotary drilling system as provided by the present invention can be best understood by again referring to FIG. 1. Where the weight of drill string 27 is being increased by the addition of portions of drill pipe as well bore 13 becomes deeper, the weight upon drill bit 22 can similarly increase unless drawworks 15 in conjunction with power unit 16 control or otherwise supports a greater portion of the weight of drill string 27. Sensor 21 and the dead line portion of the hoisting cable will provide an accurate indication of the weight of drill string 27 and therefore the weight imposed upon drill bit 22. As the weight of drill string 27 is increased, sensor 21 will initiate increased actuation of clutch and power unit 16 to provide increased torque output of clutch 85 and therefore provide increased tension in fast line 17 to support a greater amount of the weight which would otherwise be imposed upon drill bit 22. In the event the penetration rate of drill bit 22 is the pertinent parameter, appropriate use of the output of sensor 21 can adjust torque output of clutch 85 to provide for precise control thereof. A complete rotary drilling system does not exist unless the rotational speed or torque at drill bit 22 is controlled. Conventional sensors can be utilized at rotary table 26 to determine thetorque imposed upon kelly 25 and therefore the torque or speed at drill bit 22 is also known. Use of the output of the sensors at rotary drill table 26 will provide for maintaining the appropriate torque output of clutch by adjusting the air actuating elements of clutch 125. The two subsystems comprise a total cooperating system for implementing an improved method for rotary drilling which substantially surpasses the methods and apparatus for implementing same as disclosed by the prior art. Since the increased need and use of off-shore drilling techniques has substantially increased the cost of the output of the well, the present invention apparatus and method of rotary drilling provide increased efficiency and economy in the drilling of well bores.
1. A rotary drilling apparatus for controlling the support of a drill string and the rotation of a rotary drill table comprising:
a. a drawworks including a drum, a hoisting cable disposed about said drum, means for sensing the weight on said hoisting cable and an input shaft to said drawworks, whereby rotation of said input shaft is adapted to rotate said drum;
b. a first rotational power source;
0. a first continuously slipping clutch interposed between said first rotational power source and said input shaft of said drawworks;
d. a second rotational power source; and
e. a second continuously slipping clutch interposed between said second rotational power source and the rotary drill table whereby the speed of rotation of the rotary drill table and the tension in said hoisting cable is controlled.
2. A rotary drilling apparatus as defined in claim 1 wherein said first and second continuously slipping .clutches comprise an inner hub and outer housing adapted to frictionally rotate with respect to each other and liquid means for dissipating the frictionally generated heat therein, and a clutch shaft being secured to said inner hub.
3. A rotary drilling apparatus as defined in claim 2 wherein said continuously slipping clutches'include a friction disc secured to said inner hub, friction elements adapted to slidably engage and rotate within said outer housing, said liquid means for dissipating heat adjacent to the friction elements, and air actuated expandable elements secured to said housing and adjacent said friction elements whereby said friction elements frictionally engage said friction disc upon actuating said expandable elements.
i 4. A rotary drilling apparatus as defined in claim 2 wherein said first rotational power source is coupled to the outer housing of said first continuously slipping clutch, and said second rotational power source is coupled to the outer housing of said second continuously slipping clutch said frictional rotation between said respective outer housing and said respective inner hub being at a predetermined differential speed whereby the torque at said clutch shaft is controlled.
5 A rotary drilling apparatus as defined in claim 4 includingfirst and second sensing means for respectively outputting indicia responsive to the load on said hoisting cable and rotation of said rotary drill table and means for actuating the expandable elements of said first and second continuously slipping clutches respectively in response to the output indicia of said first and second sensing means respectively.
6. In combination with a drilling rig including a drill string and coupled drill bit, and a rotary drill table adapted to receive and rotate said drill string, a rotary drilling apparatus comprising:
a. drawworks including a rigid frame, a drum mounted on a drum shaft rotatably supported by said rigid frame, a hoisting cable wound about and secured to said drum an end thereof being coupled to the drill string;
b. a first power source;
c. a first continuously slipping clutch having an inner hub and outer housing adapted to frictionally rotate with respect to each other and liquid means for dissipating the frictionally generated heat therein, and a clutch shaft being secured to said inner hub and journeled on said rigid frame, said outer housing being coupled to said first power source and said clutch shaft being coupled to said drum shaft;
d. a second power source; and
.e. a second continuously slipping clutch having an inner hub and outer housing adapted to frictionally rotate with respect to each other and liquid means for dissipating the frictionally generated heat therein, and a clutch shaft being secured to said inner hub and coupled to the rotary drill table, said outer housing coupled to said second power source.
7. A rotary drilling apparatus as defined in claim 6 wherein said first and second continuously slipping clutches include a friction disc secured to said inner hub, friction elements adapted to slidably engage and rotate with said outer housing, said liquid means for .dissipating heat being adjacent said friction elements,
and air actuated, expandable elements secured to said housing and adjacent said friction elements whereby the friction elements frictionally engage said friction disc upon actuating said expandable elements.
8. A rotary drilling apparatus as defined in claim 6 including first and second sensing means for outputting indicia responsive to the load on said hoisting cable and the rotation of said rotary drill table respectively, said first sensing means coupled to the expandable elements of said first continuously slipping clutch and said second sensing means coupled to the expandable elements of said second continuously slipping clutch.
9. For use with a drilling rig including a drill string and coupled drill bit, a rotary drill table adapted to receive the drill string, a drawworks having a first continuously slipping clutch interposed between a power source and a drum of the drawworks, a hoisting cable secured to the drawworks drum and supporting the drill string, a second continuously slipping clutch interposed between the rotary drill table and the power source thereof, a load sensor interposed in the hoisting cable and the rotation sensor coupled to said rotary drill table, a method for rotary drilling of well bores comprising the steps of:
a. sensing the load on the hoisting cable;
b. adjusting the output torque of said first continuously slipping clutch to a predetermined level in response to the sensed load on the hoisting cable;
c. sensing the rotation of said drill string; and
d. adjusting the output torque of said second continuously slipping clutch to a predetermined level -in response to the sensed rotation of said rotary drill table.
10. A method for rotary drilling of well bores as defined in claim 9 including the step of simultaneously