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Publication numberUS2390646 A
Publication typeGrant
Publication dateDec 11, 1945
Filing dateMay 10, 1943
Priority dateMay 10, 1943
Publication numberUS 2390646 A, US 2390646A, US-A-2390646, US2390646 A, US2390646A
InventorsHays Russell R
Original AssigneeHays Russell R
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Well drilling apparatus
US 2390646 A
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Description  (OCR text may contain errors)

Dec. 11, 1945. R. R. HAYS WELL DRILLING APPARATUS 5 Sheets-Sheet 1 Filed May 10, .1945

% INVENTOR ATTO RN EY 3 Sheets-Sheet 2 R. R. HAYS WELL DRILLING APPARATUS,

Filed May 10, 1943 Dec. 11, 1945.

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INVE T R.

R. R. HAYS 2,390,646

DRILLING APP TUS Patented Dec. 11, 1945 UNITED STATES PATENT OFFICE WELL DRILLING APPARATUS Russell R. Hays, Lawrence, Kans. Application May 10, 1943, Serial Nb. 486,446

7 Claims.

This invention relates to well drilling apparatus and more particularly to improvements in mechanisms for cutting drainage channels transversely to a main drill hole.

Among the problems encountered in the development of cutting heads when a high pressure fluid carrying abrasives was projected against the face of an oil bearing sandstone, was one arising through the widely variegated nature of the cementing material with the result that the cutting head was held up or deflected by reason of the face of the sandstone being cut away unevenly ahead of it. A variety of cutting heads using a rotary grinding action and also a direct hammering action were tested individually and in combination with the use of abrasives in an efiort to overcome this difl'iculty. With the introduction of such mechanical movements it soon became evident that two lem were possible.

In the first, the power means might be contained within the main drill hole in which event approaches to the prob- I a comparatively heavy motor or engine might be used for motivating the cutting head; but, it was then necessary to mechanically transmit either a twisting or a reciprocatin movement through a 90 angle in order to drill transverse channels. In either case great inefliciency arose when flexible couplings were used to transmit power through an angle of this magnitude, while the use of gearing introduced great mechanical complexity and brought out the fact that with rotary drilling means a torque problem of first magnitude accompanied extension of the cutting head away from the main drill hole.

The second approach; which was the one chosen, was that of placing the drive mechanism for producing either a rotative or, hammering action of the cutting head entirely within this head or immediately adjacent thereto, thereby making a unit which was projected into a transverse channel by means of. a flexible conduit which would pass with comparative ease through a 90 turn at the bottom of the main drill hole and at the same time'supply a high pressure fluid or gas for the operation of the mechanism it carried. The greatest drawback to a mechanism of this nature appeared to lie in the requirement of extraordinary compactness since i it must be retractable into'the main drill hole with the conduit by which it was carried.

Previous experiments have shown that to successfully force a flexible conduit through a 90 angle limits the diameter of the conduit to about one-fifth the diameter of the main drill hole,

-on an extendible conduit and ,ber and such compactness of I of the drive mechanism being definitely restricted by such considerations, it was obvious that a very rapid energy exchange was necessary if work of any magnitude was to be performed. This in turn meant that a high pressure fluid stream or its equivalent must be used to operate the mechanism, and also that relatively large valves and very rugged construction of the moving parts would be required.

Space limitations and the requirement of flexibility mitigated against the use of drive mechanisms which would convert the energy of a high pressure stream to a. rotary motion, and accordingly a program of experimentation was undertaken toward the end of developing a device or machine for transmitting a hammering or striking movement to the drill head. Investigation revealed that the ordinary reciprocating action of a piston carrying a drill head was useless for the purpose in mind and led to an analysis of the hammering action of such mechanisms as standard drilling tools. steam hammers, and the like. This revealed that such hammering or drilling tools were characterized by a rhythmic beat or stroke in which the mass of the tool in question accelerated during the major portion of the "striking blow, and that the energy thus imparted was abruptly absorbed at the end of the stroke by a combination of impact against some solid object or formation and of damping by means of a powerful spring or its equivalent. Accordingly the object of this invention is broadly the provision of a small hydraulically or pneumaticallyoperated mechanism mounted providing a rhythmic beat or stroke similar in character to that of standard drilling tools to a small bit or cutting head carried ahead of the mechanism in question. Another object is the provision of a device of. this nature which has a flexible expansion chamw unyieldable ele; ments including inlet and exhaustv valves of relatively large size, valve throw mechanisms, packing glands, and the like that the whole device can be retracted into a curved passageway having a throw at least as great as the diameter of a cross-section of the conduit on which it is mounted.

Still another object is the provision of an assembly having the foregoing characteristics in which all the elements with the exception of a fluid supply tube are mounted for travel with the cutting bit of head thereby increasing the mass subject to movement and hence the work which can be performed by it.

Ancillary objectives such'as a simple arrangement of direct throw valves. a single direct reversal of the fluid supply stream, use of a single packing gland, automatic damping means to arrest the motion of the drill head assembly at the end of each stroke. means for imparting a rotary motion to the cutting bit, all in conjunction with a rugged construction of parts capable of standing up under work of this nature will be made clearer from a consideration of the following detailed description taken in connection with the accompanying drawings in which:

Fig. l is an elevational view of a drill mechanism in the expanded position embodying this invention.

Fig. 2 is a view similar to that shown in Fig. 1 with the parts shown retracted and partly broken away.

Fig. 3 is an enlarged irregular sectional view of the drilling head assembly taken on line III-III of Fig. 5 with the parts expanded.

Fig. 4 is an irregular sectional view similar to that shown in Fig. 3 with the position of the valves changed.

Fig. 5 is a cross sectional view taken on line V-V of Fig. 4.

Fig. 6 is a reduced cross sectional View taken on line VI-VI of Fig. 3.

Fig. 7 is an end elevation of the bit showing the cutting edges.

Fig. 8 is a top side view of the bit.

Fig. 9 is an enlarged fragmentary sectional view taken on line IX-IX of Fig. 1.

Referring to Figures 1. 2. and 3, a section of h gh pressure hose II] which. with the exception of the fact that its walls are impregnated with lead 9 to increase its weight, is identical with that projected transve sely from a drill holerby means of a slip-joint and flanged rol'ed arrangement such as is described in the co-pending Patent No. 2,345,816. In this instance the extending end 01 the hose I is fitted with a conventional male hose coupling H which screws into the female coupling l2 of the hydraulically operated drilling mechanism M. The coupling I2 is swedged down to carry the flexible conduit l which is similar to those used on high pressure grease guns in that although laterally flexibe it does not change its shape longitudinally when pressure is applied to its inner wall. The outer end of the fluid conduit I5 is also swedged and carries the flu d supply tube It which has a collar l1 solidly afllxed to its free end.

A drill head assembly I8 is mounted upon the tube I6 for reciprocating movement during which the tube It teescopes into the chamber 20 of the drill head. The inner end of the drill head carries a packing 2| which rides on the tube lliand prevents leakage of fluid from one side to the other of the drill head during travel thereon. Concentric with the packing 2| the inner end of the drill head has a reduced section 23 over which -is solidly aflixed the inner end of a soft rubber tube 24 with fairly heavy sidewalls. This tube 24 fits loosely over the flexible conduit l5 and its inner end is fixed to the inner end of the c n u t adjacent the coupling 12 so that a sealed chamber 21 is formed between the conduit l5 and the inner wall 26 of the tube 24 with the exception of the fluid supply port 28 and the fluid exhaust port 29 carried in the forward part of the drill head I8.

The coiled spring 30 completely covers the tube 24 and its ends extend slightly beyond corresponding ends, the inner end being solidly affixed to a suitable shoulder on the supply hose coupling i2 and the outer end being fixed to the reduced section 3| at the rear end of the drill head 18 by means of screws 32 (see Figure 5), which restrain longitudinal movement at the end of the spring relative to the drill head but permit a slight lateral flexing suflicient to permit retraction of the head and spring into a curved passageway having a, relatively small radius.

The wire of which the coiled spring 30 is made is pro-formed before coiling to give its inner face 34, Fig. 9, a wedge shape so that related wedge shaped grooves 36 lie between successive coils of the spring which contact at rounded shoulders 35. When the exhaust port 29 is closed and the inlet port 28 opened, a high pressure fluid stream enters the expansion chamber 21 and exerts a radial force F against the inner wall 26 of the soft rubber tube 25 with the result that it is forced outward through a distance D whereupon the outer face of the tube is extended as ridges 38 into the wedge shaped spaces 36 inside the coiled spring 30. Since the integrated coils of the spring 30 provide tensile resistance to outward expansion it follows that the direction of action of the force F is changed through the medium of the ridges 38 thereby providing a longitudinally effective force G and G tending to push consecutive coils of the spring apart. This force G and G is resisted only by the iongitudinal tension inherent to the spring and hence when the force G and G exceeds this tension the spring extends longitudinally.

The main portion of the drill head assembly I8, Fig. 5, consists of a circular section 40 carrying the reduced faces or shoulders 23 and 3! at its inner end upon which are mounted the forward ends of the expansion tube 24 and the co..led spring 30 respectively; a tube 50 concentric with and tel;scoping on the supply tube l6 which carries the packing gland 2| on its inner end and on its outer end a wide flange 5| containing the exhaust ports 29 and the inlet ports 28, this flange 5| being reduced in thickness at its outer periphery to form a flange 52 by means of which it is properly positioned relativeto the other parts of the head assembly; and, a head piece 6|! containing an extension of the exhaust port 29 and carrying a stud or pins 62 at its outer end on which is mounted the bit plate 10. These three 'sections, 40, 50, and 60 are centrically aligned and fixed solidly together by bolts 4| through the holes 6|, suitable gaskets 42 being placed between the faces of the sections before assembly to render the joints fluid tight. 1

The valve assembly consists of a ring 54 slidably mounted on the tube section 50 behind the flange 5| and carrying the exhaust valves 55 on one section of its rearward edge and the inlet valve stems 56 on alternate sections of its forward edge. The valve stems 56 pass through the inlet ports 28 to carry the inlet valves 51 at their outer end. The forward faces of the valves 51 have a projection 58 upon which is mounted a throw spring 63 by means of a screw 59. The inner end of the throw spring 63 projects into a groove 65 in the a throw 'ing of the valves reverses the the washer 16 and head of the pin 62 It carried at the outer end of the valve tube 81 which telescopes between the section tube 50 and the fluid supply tube It, be-

ing caused to travel with the head assembly I 8 by reason of the tensionspring G3 contacting the shoulder of groove 65, and being restrained from traveling with the drill head assembly at either end and the end flange It at its outer end contacting the end of the supply tube It. When" the valve throw tube 81 is restrained from traveling with the head assembly III, a, tension is applied to the valve throw spring 63, and when this tension becomes greater than thehydrostatic head holding either the inlet or the exhaust valves in a closed position, this tension serves to throw the valves, simultaneously ope g one and'closing the other. the arrangement of parts being such that a hydrostatic head is always available to hold any valve in a closed position. Since throwdirection of fluid movement in the expansion chamber 21. it follows that throwing of the valves in the same direction as the head assemblys travel acts to reverse the direction or this travel.

The bit assembly is terminated by a, thick conical bit plate 10, the point of which extends away from the head assembly and the rim of which extends beyond the sides of the'head assembly to form a conventional bit head flange. The center of the inner face of the bit plate 10 is recessed to receive and provide clearance for the head of the pin 62 over which it fits. The plate 10 is farther recessed to provide a shoulder 13 upon which is fixed a heavy washer 16 by means of screws to form a ball race between in which are held ball bearings 11. The inner edge of this recessed portion of the bit plate forms a shoulder 18 which contacts the outside flange of the shouldered washer 19 which restrains the bit plate from tilting relative to the pin 62 yet still permits it to swivel freely thereon. The inner face of the bit plate 10 lying outside the shoulder 18 is grooved to form the deflection vanes 12, Figs. 4 and 8, against which the exhausted fluid from the expansion chamber 21 impinges and in being deflected radially acts to set up the rotation R of the bit plate. The outer face of the bit plate 10 is also grooved, Fig. 7, to provide cutting edges 1| or ridges which are faced with extremely hard alloys.

In operation, the movement of the cutting head I8 is essentially the same as the drilling action of a string of tools on a standard rig. This should not be confused with the reciprocating action of a piston operating in a cylinder against a constant load. In the latter instance the objective is to apply a more or less constant pressure aga nst the face of the piston toward the end of producing uniform movement of a drive wheel. With a string of drilling tools, on the other hand, the objective is to producer, maximum impact of the tools against the formation to be drilled. To achieve this end the tools are swung from a walking beam which provides a reciprocating movement to a resilient drilling rope or cable, which carries the drilling tools on its free end.

Withthis picture clearly in mind it is evfdent that to obtain an effective hammerin action of, the drill head of a device for cutting transverse drainage channels, the energy exchange by which the drill head is motivated should parallel that which experience has shown to be effective. Sin"e gravity is not available to accelerate the drill head on the out stroke or to damp its movevalve sorbed by the went on the back stroke, it follows that the genutilizing a relatively heavy spring 30, Figs. 1 and intermediate the drill head It andlthe fluid supply hose [0 so that when the head is extended by whatever means are available to arrest the cutting head;

used, this spring will be outward movement 01' the at which time the force thus abspring acts directly against the supply hose rather than being transmitted to the valve assembly and restraining flanges carried by then apparent that if the mass, of the supp y hose is .very great relative to the the head. It is mass of the drill head, which in this instance is achieved by leading the former, then elements equivalent to those efl'ective at the end of the down stroke of standard tools have been supplied.

However, it is equally apparentthat a single spring in itself does not duplicate the action of standard tools since with the latter the walkin beam drops the tools and the spring tension of the drilling cable becomes effective in arresting or damping their downward action only at the end of the stroke. It is desirable therefore to nullify the tension of the spring during the major Portion of the out-stroke, but to retain the full force of its resistance to damp the cutting head at the very end of th s stroke. This is accoms plshed by what is in efi'ect another spring placed under compression at the beginning of the stroke, specifically, the rubber fingers 38 of the expansion tube 2, which act to spread consecutive coils of the spring 30 apart until the head is nearly to the end of its outward stroke. As long as fluid pressure is applied to the chamber 21 to the extent that the forces G and G, Fi 9. approach the tension inherent to. the spring 30, and the force required to expand the spring will be only the difference between the two. and when the fluid pressure is released atany time during expansion of the chamber 21 the entire tension of the spring 30 will be ava lable to resist outward movement of the drill head.

Hence, after the fluid pressure in the expansion chamber 21 is released, the entire outward inertia of the drill head I8 is absorbed by the spring 30 under ofl' bottom conditions, and this kinetic energy is then available to bounce the head backwards. Fluid meanwhile being exhausted from theports 29 thereby releasing the compression against the walls 26 of the expansion chamber 21 and hence nullifying the force G and G, the entire tension of the spring 30 is available to return the drill head [8 to its initial position. And it will be further apparent that by closing the exhaust port 29 before the spring 30 has completely con tracted, any residual tension in it will be absorbed by recompression of the resilient fingers 38 imposed in the wedged recesses 36.

- Coincident with this automatic release of the force G and G near the end of the out-stroke and the replacement of it at the end of the in-stroke subsequent to the opening and closing of the inlet and exhaust ports 28 and 29 respectively, the hydrostatic head of the expansion chamber 21 exerts a force, tending to thrust the cutting head l8 outward, equal to the cross-section of the chamber times the hydrostatic head in the same fashion that such force is efiective upon a conventional piston operating in a cylinder. To be sure, this force acts both fore and aft, but since the mass of the head I8 is only a fraction of that of the leaded supplyhose l0, it results primarily in movement of the drilling head only.

The action of the reciprocating movement of the drilling head It on the supply tube [8 in opening and throwing the valve assembly 54 to it follows along conventional lines. A high pressure fluid stream entering the recessed portion of the drill head [8 throughthe supply tube l8, passes through the inlet port 28 into the expansion chamber 21. Since the exhaust port 29 is closed, the exhaust valve 55 being integral with the inlet valve 51, the hydrostatic head of the supply line is applied to the inside of the expansion chamber. Two actions occur simultaneously; first, pressure is created on the walls of the chamber, thereby nullifying the tension of the spring 30; second, the pressure acting outwardly tends to force the cutting head l8 outward over the supply tube I6. As this movement continues, the flange 88 of the valve throw tube 61 contacts the flange l1 at the end of the fluid supply tube It, with the result that outward movement of the valve throw tube with the drill head assembly is stopped. Since the head It continues to move outward, tension is applied to the valve throw spring 83 by reason of its end being retained in the groove 65 of the flange on the valve throw tube. When the tension on this spring becomes greater than the force holding the exhaust valve 55 closed, this being the cross-section of the exhaust port times the hydrostatic diflferential between the chamber 21 and the fluid outside it, the exhaust valve is thrown open and the inlet valve 51 is closed, being held in position by the pressure differential between the fluid supply stream and the now exhausting expansion chamber 21.

Since the greatest force to be overcome by the tension in the spring 63 occurs at the instant of opening either the valve 55 or 51, it follows that the tension therein will serve to throw the valve with considerable force to the position in which the opposite ports are closed. By reason of this throw. or distance through which the valves move, the inner end of the spring 63 which had contacted the face of the groove 65 at the time it was being placed under compression, travels with the valve which has moved relative to the valve throw tube 61 so that now the inner end of the spring is clear of the face of the groove .65 and no longer under tension. Inasmuch as the width of the groove 55 is equal to the throw of the valves 55 and 51, it follows that the drill head l8 may, through inertia, continue moving outward after throwing of the valves for a distance equal to the width of the groove 85, without having any efiect on the valve throwing mechanism.

During this time however, its outward movement is arrested either by the tension of the coiled spring 30, or by reason of the bit contacting the formation to be cut, or by both.

Whle the head is continuing on outward and reversing its direction of travel, the fluid contained in the expansion chamber 21 is already exhaustin through the now open port 29. This relieves the pressure on the sidewalls and hence decreases the forces G and G effective against the inside face of the spring 30. As the expansion chamber continues to exhaust, the drilling head I8 is withdrawn on the supply tube l6 by the tension in the coil spring 30 until the outer flange 6.6 of the valve throw tube 61 is contacted by the outer side of the flange l1 on the supply tube [6. When this occurs tension is again applied to the valv throw spring 63 through farther withdrawal of the drill head, but this time in the opposite direction. Consequently, when this tension becomes greater than the hydrostatic differential holding the inlet .valve 51 closed, which differential has now increased upon exhausting of the chamber 21 so that it approximated that which held the exhaust valve shut at the other end of the stroke, the inlet valve is thrown open and the exhaust valve closed. This acts to retain any fluid in expansion chamber and to give it the pressure of the supply stream. As a result any farther rearward movement of the drilling head by reason of its rearward inertia is' damped through the medium of the wedged faces of the spring 30 contracting on the fingers 38 of the expansion tube 24. The expansion chamber now begins to fill again and the process is repeated.

Experience has shown that when any cutting bit having serrated edges on its face is used on a, churn drill it is very desirable to rotate the bit with each stroke. Consequently, the bit plate is mounted for swiveling action upon the pin 62 and the exhaust stream utilized to whirl it during each return stroke of the head through the medium of the stream impinging against the vanes 12 carried on the inside of the bit plate 10. This also serves to flush the face of the drill hole with each stroke; the cuttings being pickedup by this exhaust stream and floated to the surface as has been more fully described in the co-pending Patent No. 2,345,816.

The advantages of a drilling mechanism of this nature for cutting transverse channels in fluid bearing formations, or any other type of channel so situated that it cannot be reached by conventional drilled tools; being self-evident from the foregoing description, what is claimed is:

1. In pneumatic engines, a fluid pressure supply conduit, a longitudinally extensible chamber comprising a soft rubber tube surrounded by a helical spring, a head carried by the extending end of said coiled spring, inlet and exhaust ports carried by said head, a valve structure alternately operative to control sa d ports, a spring tension means carried by the extensible end portion of said chamber for throwing said valve structure,

a restraining means integral with the relatively of the extensible chamber whereby the operations of the valve structure are synchronized with the reciprocal movement of the head carried by the coiled spring, in response to tension thus induced in said spring tension means.

2. In a pneumat c engine. a fluid pressure supply conduit, a longitudinally extensible cylinder carried by and communicating with said conduit, a head carried by said cylinder having an inlet port and an outlet port for said cy1indel,'interconnected valves for said ports, a valve throw spring carried by said interconnected valves, means carried by said conduit in the. path of travel of said throw spring, pneumatic means normally holding said interconnected valve members in fixed relation relative to said ports and for extending said cylinder, and a helical spring operable to contract said cyl nder whereby fluid under pressure is intermittently delivered to said cylinder to cause a reciprocation of said head.

3. In a pneumatic engine, a fluid pressure supply conduit, a longitudinally extensible cylinder carried by and communicating with said conduit. a head mounted on the forward end of said extensible cylinder having an inlet port and an outlet port for said cylinder,

-of, whereby said valves interconnected valves for said Ports, a valve throw spring carried by said interconnected valves, means carried by said supply conduit to engage said throw spring, pneumatic means normally for holding said interconnected valve members in fixed relation relative to said ports and for reciprocating said head including a helical spring surrounding said extensible cylinder and resisting the extension thereare caused to operate as said head is reciprocated to cause said throw spring to overcome said pneumatic means.

4. In a well drilling mechanism for drilling lateral holes from a well bore, a pressure fluid supply conduit, an elastic tube constituting a longitudinally expansible and transversely flexible chamber communicating with and secured to said conduit. a drill head having an outlet port and carried on-the free end of said chamber, and a valve responsive to the fluid flow in said chamber to open and close said outlet port whereby the fluid .flow in said chamber is varied to cause expansion and contraction of said chamber whereby said drill head is reciprocated. v

, 5. In a well drilling mechanism for drilling lateral holes from a well bore, a pressure fluid supply conduit, an elastic tube constituting a longitudinally expansible and transversely flexible chamber communicating with and secured to said conduit, a drill head having an outlet port and carried on the free end of said chamber, a valve responsive to the fluid flow in said chamber to open and close said outlet port whereby the fluid flow in said chamber is varied to cause expansion and contraction of said chamber whereby said drill head is reciprocated, and resilient means for limiting outward movement oi! said drill head.

6. In a well drilling mechanism for drilling lateral holes from a well bore, a pressure fluid supply conduit, an elastic tube constituting a longitudinally expansible and transversely flexible chamber communicating with and secured to said conduit, a drillhead having an outlet port and carried on the free end of said chamber, a valve responsive to the fluid flow in said chamber to open and close said outlet port whereby the fluid flow in said chamber is varied to cause expansion and contraction said drill head is reciprocated, a drill bit plate integral with said drill head, and vanes formed in said drill bit plate and obliquely disposed to the path of travel of fluid from said chamber whereby said bit plate is rotated.

7'. In a well drilling mechanism for drilling lateral holes from a well bore, a pressure fluid supply conduit, an elastic tube constituting a longitudinally expansible and transversely flexible chamber communicating with and secured to said conduit, a drill head having an outlet port and carried on the free end of said chamber, a valve responsive to the fluid flow in said chamber to open and close said outlet port whereby the fluid flow in said chamber is varied to cause expansion and contraction of said chamber whereby said drill head is reciprocated, and a flexible nonextensible conduit extending into said chamber and operatively associated with said valve.

RUSSELL it. Have.

of said chamber whereby

Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US2441881 *Jul 13, 1945May 18, 1948Hays Russell RHydraulic expansible chamber motor with longitudinally extensible cylinder
US2554005 *Dec 11, 1950May 22, 1951Soundrill CorpEarth boring apparatus
US2667144 *Nov 21, 1949Jan 26, 1954Hughes Tool CoRotary and impact tool
US3435905 *Mar 29, 1966Apr 1, 1969Lazarus & Peyser AssociatesTool and method of manufacturing the same
US3439756 *Jan 29, 1965Apr 22, 1969Guin Joel BHigh speed vibration drills
US3624760 *Nov 3, 1969Nov 30, 1971Bodine Albert GSonic apparatus for installing a pile jacket, casing member or the like in an earthen formation
US3958649 *Jul 17, 1975May 25, 1976George H. BullMethods and mechanisms for drilling transversely in a well
US4299298 *Jul 10, 1980Nov 10, 1981Boart International LimitedDown-the-hole drilling
US4554982 *Aug 3, 1984Nov 26, 1985Hydril CompanyApparatus for forming boreholes
US6220372Dec 4, 1997Apr 24, 2001Wenzel Downhole Tools, Ltd.Apparatus for drilling lateral drainholes from a wellbore
US6338390Jan 12, 1999Jan 15, 2002Baker Hughes IncorporatedMethod and apparatus for drilling a subterranean formation employing drill bit oscillation
Classifications
U.S. Classification173/59, 175/107, 91/49, 175/189, 175/56, 175/232, 175/79, 173/218, 91/50
International ClassificationE21B4/00, E21B4/02, E21B7/04, E21B7/24, E21B4/16, E21B7/00, E21B7/08, E21B4/14
Cooperative ClassificationE21B4/02, E21B4/16, E21B7/24, E21B4/14
European ClassificationE21B7/24, E21B4/14, E21B4/16, E21B4/02