US3650337A

US3650337A - Cryogenically cooled drill

Info

Publication number: US3650337A
Application number: US846478A
Authority: US
Inventors: Donald W Andrews; Eugene L Kessler; Roland A Newton
Original assignee: Aerojet General Corp
Current assignee: Aerojet Rocketdyne Inc
Priority date: 1969-07-31
Filing date: 1969-07-31
Publication date: 1972-03-21
Anticipated expiration: 1989-03-21

Abstract

This discloses a drilling unit in which the drill bit mechanism is placed at the end of the rotor shaft of a motor either by direct attachment to the shaft or by gear. Cryogenic cooling is provided by sending cryogenic fluid into the rear portion of the motor and causing it to flow toward the front end of the motor for cooling the motor, effluent from the motor being conveyed into and through the drill bit and through bearings and gearing, for cooling and cleansing. The coolant effluent from the drill bit mechanism and motor passes into the bore hole thereby cooling it and carrying cuttings and debris upwardly through the hole.

Description

United States Patent Andrews et al.

[45] Mar. 21, 1972 [541 CRYOGENICALLY COOLED DRILL 3,424,254 1/1969 Huff ..175/17 [72] Inventors: Donald W. Andrews, Eldorado Hills; Eu-

g i g L. Kessler; Roland A. Newton both p f Sacramento an of Cahf' Primary Examiner-James A. Leppink Assignee: A i Corporation. l Monte, Attorney-Edward o. Ansell, D. Gordon Angus and Donald Calif. 1 W. Graves 22 Filed: July 31, 1969 [57] ABSTRACT N 4 478 [2 l 1 P 8 v This discloses a drilling unit in which the drill bit mechanism is placed at the end of the rotor shaft ofa motor either by direct U.S. Cl tta h ent to the haft o g'ean Cryogenic goofing is pro. [51] Int. Cl ..'...E2lb 3/10 vided by Sending cryogenic d i the rear portion of the [58] Fleld of Search ..l75/ 17, 69, 71, 104, 107; motor and causing it to n toward the from end of the motor 166/302 for cooling the motor, effluent from the motor being conveyed i into and through the drill bit and through bearings and gear- [56] References C ted ing, for cooling and cleansing. The coolant effluent from the UNITED STATES PATENTS drill bit mechanism and motor passes into the bore hole 175/17 thereby coollnlg it and carrying cuttlngs and debris upwardly 2, l l Mackay through the ho e 2,355,342 8/1944 Van Wormen ..l75/l04 3,181,631 5/1965 Nielsen 175/104 20 Claims, 3 Drawing Figures 42 /7 24 so 2267 /Z8 45 /6 46 34/ /6 23 25 m 5o /s 47 5 /Z [4 a, 461 52 2s 3/ Z 2] /o/ 35 CRYOGENICALLY COOLED DRILL This invention relates to earth drilling equipment and method of drilling, and has for an object to increase the speed or penetration rate and the directional accuracy with which very long or deep holes are bored.

The invention is applicable to oil, water and gas well drilling, rock boring for shot holes, seismic bore holes and the like. The term earth-drilling as used herein means drilling through anything found in or on the earth, including drilling under water.

It is well known that the speed and efficiency of earth drilling is improved by cooling the drill bits, and coolants and refrigerants have heretofore been used with earth-drilling bits and equipment.

In accordance with the present invention, there is provided a more efficient organization of cooled power drilling equipment than has heretofore been known. The invention is carried out by use of a unitary arrangement of a cryogenic-cooled motor suspended by cable or other support means at the work surface with means for transmitting the power from the motor to the cutters, mounted in close proximity to the motor. Means is provided which conveys cryogenic fluid directly from the motor to the cutter mechanism from where it emerges into the borehole from which it emerges with the cuttings.

A feature of the invention resides in provision for transmitting to the motor the cryogenic coolant, such as liquid nitrogen or other liquefied gas. It is preferred that the electric supply cable to the motor shall be immersed in the cryogenic supply fluid to reduce electrical resistivity of the cable.

According to other features, the cryogenic coolant is channeled through and around the electric motor in a manner to reduce the temperature of the motor to or near the cryogenic fluid temperature. Thus the electrical resistivity of the motor is reduced. The arrangement provides a motor of great power density located at the work area.

During motor operation, heat rejected by the motor is absorbed by the cryogenic fluid coolant. Effluent from the motor is routed through flow circuitry from the motor to and through the drill cutter and bearings to cool and clean these parts. Effluent from the motor may be a liquid, a gas, or a mixture of both.

Gaseous effluent emanating from the drill, in addition to maintaining the cutting and the work surface at a very low temperature, clears the work area of cuttings and is the medium on which the cuttings are carried out of the hole.

The foregoing and other features of the invention will be better understood from the following detailed description and the accompanying drawing, of which:

FIG. 1 is a side view partially in cross section of a drill bit and driving motor unit according to this invention;

FIG. 2 is an end view of the drill bit of FIG. 1; and

FIG. 3 is a side view, partially in cross section of another form of drill bit and driving motor unit according to this invention.

Referring to FIGS. 1 and 2 of the drawing, there is shown an electric motor comprising a cylindrical housing 11 and a rotor 12 within the housing. The rotor is shown as a cylindrical member rotatable within its housing by ball bearings 13 at the forward end and a similar bearing 14 at the rear end. A pipe nipple or the like 15 admits the electric cable containing the conductors for powering the motor. Since the internal elements by which the rotor of the motor is torqued are no part of the present invention, such elements are not shown.

At the forward end of the electric motor, and coaxial therewith, there is fastened a drilling mechanism 16. This comprises a cutter cage 17 comprising a cylindrical member 18 of somewhat greater diameter than that of the motor secured to the cylindrical motor housing 11 near the forward end of the motor housing by a ball bearing mechanism 19 providing freedom of rotation between the motor housing and the cutter cage. The balls 20 of this ball bearing mechanism are held between concentric ball races, the inner race 21 being securely fitted to the motor housing and the outer ball race 22 being securely fitted to the upper flange of the cutter cage.

A number of generally conical cutters 23, which may ordinarily be one, two or three in number (twobeing shown in the drawing), are rotatably mounted within the cutter cage with their forward cutting surfaces protruding somewhat beyond the forward end 24 of the cage. These rotary cutters are mounted to the cage by ball bearing mechanisms25 each comprising a ball race 26 fastened in a cylindrical seat within the cutter cage and another ball race 27 fastened to a rearward hub 28 of the conical cutter, with provision for maintaining the balls 29-within the ball races. The axis of rotation of each rotary cutter extends obliquely toward the, central longitudinal axis of the cutter cage and motor, as shown. A hub- 30 between the cutting portion and the rearmost hub 28 of each cutter is provided with gear teeth 31 arranged concentric with the axis of rotation of the respective cutter, All the cutters are driven in rotation by bevel gear teeth 32 formed at the forward end 33 of the rotor of the motor which protrudesforwardly from the rotor housing within the cutter cage, and these bevel gear teeth mesh with the gear teeth 31 of the respective cutters.

The cutters will ordinarily have on their conical surfaces sharpened spiral cutting ridges which are hard faced, for example with tungsten carbide or other sintered metal carbide. They may, if desired, be set with industrial diamonds for very hard formation cutting. The cutters are offset and overlapping to cut uniformly over the bottom of the hole. When a plurality of cutters are used in a cutter cage they should be circumferentially equally spaced. The cutters may be positioned so that their cutting surface is flat and horizontal, or it may be shaped as desired.

The drilling unit is provided with a cooling system for operation by cryogenic fluid. This comprises a passageway 34 within the wall of cylindrical housing 11 of the motor, this passageway extending spirally around the rotor and within the housing wall. The fluid inlet of this passageway is connected to a suitable pipe fitting or nipple 35 through the rear wall of the motor for attachment to a conduit leading from an external supply source of cryogenic fluid (not shown). The exit end of the spiral conduit connects with bores 36 and 37 through the motor housing to the exterior thereof, in position to communicate with an annular recess 38 of the cutter cage which in turn communicates with bores 39 extending forwardly through the material of the cutter cage to the rear ends of hubs 28 of the conical cutters.

There is a space 40 between the rear end of each hub 28 and the corresponding circular surface 41 of the cage through which the cryogenic fluid can flow into communication with the ball bearings 25 and then out of the cage through space 42, past gear teeth 31 and out of the cage in the space between the forward end 24 of the cage and the conical cutters. Each conical cutter has a passageway 42 extending along the axis of rotation of the cutter for communicating with space 40 and leading to a position 44 near the apex of the cutter. Each cutter also has several

lateral passageways

45, 46, and 47 communicating with the main channel 43 through the central part of the cutter and leading to the exterior of the cutter. A relatively small passageway 48 communicates with the forward end of channel 43 leading to the exterior at the apex of each cutter.

Each channel 39 passing through the material of the cage is provided with a branch channel 49 extending from channel 39 to a position nearer the central axis of the unit from which a narrow passageway or nozzle 50 leads to a space 51 formed between the part 30 of each conical cutter and the cage, at the vicinity of the gear teeth 32 so that fluid can flow lengthwise through and past the gear teeth to a central space or void 52 between member 33 and the conical cutters. The space 52 is in communication with the lateral channels, 45, 46 and 47 When electric power is applied to the motor, the rotor will rotate the conical cutters by means of the meshing bevel gears 32. Although the cutter cage is free to rotate relative to the motor housing, it will be subject to considerable drag force from the bore hole and the elements in it so that whatever rotation the cage has will be minor as compared with the speed of rotation ofthe rotor of the motor.

In its flow cycle, the cryogenic fluid, for example liquid nitrogen, will reach the inlet to the spiral passageway 34 of the motor housing below its critical temperature at whichthe liquid becomes gaseous. During the course of its flow through the passage 34 a portion of the liquid fluid may be flashed to the gaseous state by heat rejected from the cryo-motor. This gas, together with the remainder of the cryogenic flow through the motor housing arrives at the gear coolant nozzles 50 and the cutter nozzles 48 and the lateral passageways where it is expanded from the coolant system working pressure to ambient-bore hole pressure, resulting in its transformation to the gaseous state. This transformation makes use of the latent heat of vaporization of the cryogen, thus increasing the cooling capacity at the work surface. The resultant gas effluent cools and cleans the gear system and the cutters, as well as removing cuttings from the work area.

The very cold gas leaving the cutting area carries with it the cuttings, and as the column of chip-containing gas rises up out of the hole, it picks up heat rejected from that portion of the bore hole wall already cut, freezing the wall and accelerating the gas velocity in proportion to the decrease in gas density.

FIG. 3 shows another form of drilling unit which is the preferred embodiment of this invention. A principal difference from the embodiment of H6. 1 resides in the use of only a single drill bit, which is attached directly to the rotor shaft and without any gears. In other respects the embodiment of FIG. 3 does not differ greatly from that of FIG. I. The electric motor 55 is similar to the motor of FIG. 1 in that it has a cylindrical housing 56 with a rotor within it having a shaft 57 rotatable within the housing by means of ball bearings at the forward and rear ends, of which only the forward bearing 58 is shown. The cylindrical housing is somewhat similar to that of FIG. 1 in that it contains a spiral passageway 59, the inlet end of which is in communication with an inlet pipe 60 through which the cryogenic fluid enters the passageway. The electrical conduit for driving the motor (not shown) will also pass through this inlet pipe 60 into the motor.

Instead of having a plurality of drill bits as the forward end of the rotor shaft, there is provided only a single drill bit 61, this having a shank 62 provided with means for attachment to the forward end of the rotor shaft which protrudes from the housing. While any suitable attaching means may be used, the means shown are internal threads 63 on the shank which thread tightly onto external threads on the shaft. The rear end of the shank substantially meets the ball bearing arrangement 58 which is held in place by a suitable retaining ring 64 set into a groove in the housing. A sealing ring 65 helps in keeping dirt and debris from moving back to the ball bearing.

The drill bit is formed to leave a space 66 between the end of shaft 57 and the material of the drill bit. This space 66 communicates with a central passageway 67 which extends all the way through the rotor shaft along its longitudinal axis from the rear to the forward end so that the rear end of the passageway 67 communicates with conduit 60 and the forward end communicates with space 66. There extends forwardly from the space 66, along the axis of rotation, but terminating short of the forward end of the drill bit, a passageway or channel 68, and from thisaxially extending channel there branch out from the sides through the drill bit a number of laterally extending passageways 69 leading to the exterior of the drill bit. Other passageways 70 extend laterally from space 66.

The forward end of the spiral conduit 59 through the motor housing communicates with a passageway 71 leading into annular space 72 behind the bearing 58, so as to communicate with the bearing and thense with an annular space 73 in front of the bearing. The. construction of the seal ring 65 is such that fluid in space 73 can be forced through the material or convolutions of this seal to the exterior of the drilling unit through a space 74 between the hub of the drill bit and the forward end of the motor housing.

In operation of the unit of FIG. 3, when the electric power has turned on the motor, the drill bit fixed to the motor shaft turns with the shaft, and at the same time the cryogenic fluid is forced through the entrance pipe into the motor housing which it divides so that part of this coolant flows through the shaft passageway 67 while the other part flows through the spiral passageway 59. That part of the coolant fluid which passes through the shaft passageway 67 enters the space 66 from where it divides to exit from the surface of the drill bit through the various passageways 68, 69 and 70, thereby cleansing the cutting surfaces of the drill and carrying away the cuttings up the bore hole in the manner described in connection with the embodiment of FIG. 1. That part of the coolant which passes through the spiral passageway 59 flows from space 72 and through the ball bearing thereby cleansing and cooling the bearing and then out through the seal ring and space 74 to the bore hole.

The maintenance of a very cold work area and tool temperature through the use of cryogenic cooling, according to this invention, will vastly increase the tool life as compared with tools which are not cryogenically cooled.

The positioning of a high-power density motor, as abovedescribed, in the confined work space of the bore hole, through use of the cryogenic-cooled design permits a greatly improved penetration rate capability due to higher power available at the work face for a given hole diameter.

The freezing of the work area by the cold effluent from the cutters serves to prevent balling or gumming of the cutters in some formations.

The cryogenic fluid by freezing the work surface will cause 'wet gumming formations, such as shale, to become hard and competent, and hence easy to drill. The freezing makes all formations appear to the drill to be nearly the same in competence, strength, hardness and drillability, thereby avoiding the necessity for making special provision for different drilling conditions and different kinds of formations.

The heat capacity of the drilling system will, because of the presence of the very cold cryogen and also the effect of latent heat of vaporization of the cryogen, keep the drill bit cold, thereby increasing the life of the bit, and will cause the hole walls to freeze for a significant distance above the work surface, thus maintaining a competent hole wall while keeping out water, oil, gas and other undesirable inflow, and reducing the necessity for frequent casing operations.

lt has been found that chip removal by gaseous nitrogen effluent according to the present invention, is much improved over that experienced in conventional air-gas drilling, because the cryogenic gas is heated due to earth temperature as the gas rises up the hole, and this heating causes an increase in gas velocity while moving up the hole. This increase of velocity improves the chip removal capability as a function of distance up the hole.

It has been found that the cryogenic cooling provided by use of the present invention allows a much higher drill rotational speed than in conventional drilling procedures, thereby permitting lower drill bit face pressure than in conventional procedures, which in turn greatly improves the directional stability especially in sloping formation and hole wall smoothness, as well as increasing the drilling penetration rate and the bit life.

What is claimed is:

1. A power-driven, coolable drill unit for boring a hole in earth comprising a cryo-motor having a rotor and a housing which surrounds said rotor, a shaft, said rotor being connected to said shaft, and said drill bit means fastened at the forward end of said shaft, said drill bit means having a drill face, coolant conduit means for the unit comprising a passageway for fluid coolant through said motor within the wall of the housing which exits from the housing at the exit means, said fluid passageway being in the form of a spiral around said rotor,

said passageway having coolant fluid inlet means into said motor and exit means at a more forward part of said motor than the inlet means, said passageway means being in communication with said exit means and passing through said drill bit means to its exterior, said coolant fluid in said passageway means being substantially a cryogenic liquid which is flashed to its gaseous state adjacent said drill face whereby coolant fluid introduced at the fluid inlet means passes through said motor and said drill bit means to the bore hole.

2. Apparatus according to claim 1 wherein said cryogenic liquid which is flashed to its gaseous state adjacent said drill face renders various earth formations of different character to be of substantially similar competence, strength, hardness and drillability relative to the drill bit means.

3. Apparatus according to claim 1 including bearing means in which the shaft is mounted for rotation relative to the housing, in which the passageway within the wall of the housing is in communication with the bearing means.

4. Apparatus according to claim 1 in which gear means is providedfor drivably attaching the drill bit means to the rotor.

5. Apparatus according to claim 1 in which a cage is attached to the forward end of the motor and the drill bit means is rotatably mounted in bearing means within the cage.

6. Apparatus according to claim 1 in which the coolant conduit means includes a fluid passageway within the cage in communication with the passageway for fluid coolant through the motor and leading to the drill bit means.

7. Apparatus according to claim 1 in which the drill bit means contains conduit means communicating with the fluid passageway within the cage, and leading to the exterior of the drill bit means to expel coolant fluid into the bore hole.

8. Apparatus according to claim 1 in which the bearing means is included in the coolant conduit means.

9. The method of earth drilling which comprises powering a drill bit means by a cryo-motor to which the drill bit means having a drill face is drivably attached, introducing cryogenic fluid into the motor in the liquid state below the critical temperature of the fluid to absorb heat rejected from the motor, conveying cryogenic fluid out of the motor and through the drill bit means in substantially a liquid state, and flashing said cryogenic fluid to its gaseous state adjacent said drill face while ejecting it from the drill bit means.

10. The method according to claim 9 wherein the cryogenic fluid ejected from the drill bit means flashes to a gas adjacent said drill face and across the work surface, which method includes cooling the bit and work surface by vaporization, and the existent low temperature, and carrying the cuttings out of the bore hole with the effluent gas.

11. The method according to claim 9 wherein cryogenic fluid is ejected from the drill bit means and includes freezing the work surface to render various formations of different character to be similar in competence, strength, hardness and drillability relative to the drill bit.

12. The method according to claim 10 wherein the cryogenic gas is heated by the surrounding earth as the gas rises up the hole, said gas increasing in velocity in its upward movement, facilitating chip removal.

13. The method according to claim 9 wherein the cryomotor has a rotor means supported by a bearing means, said method including the step of cooling the bearing means with at least some of the coolant fluid introduced into the motor.

14. The method according to claim 9 wherein said cryomotor has a housing surrounding a rotor and said housing has a wall with a passageway therein, said method including the step of absorbing heat rejected from said cryo-motor into cryogenic fluid passing through said passageway, said cryogenic fluid passing through said passageway being at least some of the cryogenic fluid introduced into the motor.

15. The method according to claim 14 wherein the cryogenic fluid passing through the passageway of the motor housing wall is sent in a spiral path around the rotor.

16. The method according to claim 14 wherein at least some of the cryogenic fluid introduced into the motor is conveyed to said drill bit means throu h said rotor 17. A power-driven coo able drill unit for boring a hole in earth, comprising a cryo-motor having a shaft, a rotor mounted on the shaft and a housing which surrounds the rotor, said housing having a wall, drill bit means drivably attached to the shaft at the forward end of the motor, and coolant conduit means for the unit comprising a passageway for fluid coolant through the motor and including at least a spiral passage within the wall of the housing, said passageway having coolant fluid inlet means into the motor and exit means at a more forward part of the motor than the inlet means, and passageway means in communication with said exit means and passing through the drill bit means to its exterior, whereby coolant fluid introduced at fluid inlet means passes through the motor and the drill bit means to the bore hole.

18. Apparatus according to claim 17 wherein a cage is attached to the forward end of the motor and the drill bit means is rotatably mounted in bearing means within the cage, a gear means is mounted on the shaft for driving the drill bit means, and the coolant conduit means includes a fluid passageway within the cage in communication with the passageway for fluid coolant through the motor and leading to the drill bit means.

19. Apparatus according to claim 18 wherein the drill bit means contains conduit means communicating with the fluid passageway within the cage and leading to the exterior of the drill bit means to expel coolant fluid into the bore hole.

20. Apparatus according to claim 19 wherein the bearing means is included in the coolant conduit means.

Claims

1. A power-driven, coolable drill unit for boring a hole in earth comprising a cryo-motor having a rotor and a housing which surrounds said rotor, a shaft, said rotor being connected to said shaft, and said drill bit means fastened at the forward end of said shaft, said drill bit means having a drill face, coolant conduit means for the unit comprising a passageway for fluid coolant through said motor within the wall of the housing which exits from the housing at the exit means, said fluid passageway being in the form of a spiral around said rotor, said passageway having coolant fluid inlet means into said motor and exit means at a more forward part of said motor than the inlet means, said passageway means being in communication with said exit means and passing through said drill bit means to its exterior, said coolant fluid in said passageway means being substantially a cryogenic liquid which is flashed to its gaseous state adjacent said drill face whereby coolant fluid introduced at the fluid inlet means passes through said motor and said drill bit means to the bore hole.

4. Apparatus according to claim 1 in which gear means is provided for drivably attaching the drill bit means to the rotor.

13. The method according to claim 9 wherein the cryo-motor has a rotor means supported by a bearing means, said method including the step of cooling the bearing means with at least some of the coolant fluid introduced into the motor.

14. The method according to claim 9 wherein said cryo-motor has a housing surrounding a rotor and said housing has a wall with a passageway therein, said method including the step of absorbing heat rejected from said cryo-motor into cryogenic fluid passing through said passageway, said cryogenic fluid passing through said passageway being at least some of the cryogenic fluid introduced into the motor.

16. The method according to claim 14 wherein at least some of the cryogenic fluid introduced into the motor is conveyed to said drill bit means through said rotor.

17. A power-driven coolable drill unit for boring a hole in earth, comprising a cryo-motor having a shaft, a rotor mounted on the shaft and a housing which surrounds the rotor, said housing having a wall, drill bit means drivably attached to the shaft at the forward end of the motor, and coolant conduit means for the unit comprising a passageway for fluid coolant through the motor and including at least a spiral passage within the wall of the housing, said passageway having coolant fluid inlet means into the motor and exit means at a more forward part of the motor than the inlet means, and passageway means in communication with said exit means and passing through the drill bit means to its exterior, whereby coolant fluid introduced at fluid inlet means passes through the motor and the drill bit means to the bore hole.