US2257733A

US2257733A - Apparatus for drilling terrestrial bores

Info

Publication number: US2257733A
Application number: US237769A
Authority: US
Inventors: William R Coleman
Original assignee: Individual
Current assignee: Individual
Priority date: 1938-10-29
Filing date: 1938-10-29
Publication date: 1941-10-07
Anticipated expiration: 1958-10-07

Description

Oct. 7, 1941. w. R. COLEMAN- 7 2,257,733

APPARATUS FOR DRILLING TERRESTRIAL BORES Fil ed Oct. 29,1958 3 Sheets-Sheet 1 E r-I x o o O l l ll I as INVENTOR Oct. 7, 1941. w COLEMAN 2,257,733

APPARATUS FOR DRILLING TERRESTRIAL BORES I Filed Oct. 2Q, 1958 3 gheets-sheet s INVENTOR Patented Oct. 7, 1941 NT OFFICE APPARATUS FOR DRILLING TERRESTRIAL BORES i William R. Coleman, Birmingham, Ala. Application October 29, 1938, Serial No. 237,769

17 Claims.

The invention relates to apparatus for drilling terrestrial bores, and consists in improvements in structure, by virtue of which the apparatus may be constructed and operated more economically.

In accordance with the aims of the invention, the improved apparatus drillsfaster; it operates on less power; it is adapted to pump out the cuttings and fluid from the bottom of the well during the drilling-operation; it permits accurate-study and gauging of the force and speed at which the drill attacks the earth, sand, or rock through which it is working; and it permits coordination of rate at which the tool is fed with the length of stroke, with the number of strokes per minute, and with the intensity of the force with which the tool attacks the terrestrial formation being drilled. v

In the accompanying drawings Fig. I is a fragmentary view, showing inside elevation a manually operated drilling apparatus, in which the invention is embodied; and illustrating in vertical section the bore of a well being drilled; I

Fig. II is a view comparable with Fig. I, illustrating an embodiment of the inventionin a more elaborate, power operated drilling rig;

Fig. III is a fragmentary view, showing the upper portion of the rig of Fig. II, to larger scale, and partly in side elevation and partly in vertical section; I V I V 1 Fig. IV is a fragmentary view, partly insection and partly in side elevation, of the portion of the apparatus that extends immediately below that which is shown in Fig. III;

And Fig. V is a fragmentary view, in axial sec tion and to still larger scale, of the tool and pump members included in the drilling apparatus.

The apparatus of the invention includes a drillingtool secured to the lower end of a vertical drill-supporting member, which advantageously consists in a tubular drill-rod. The rod and tool assembly is suspended from and supported by an expansible and corn ressible medium, and as so suspended and supported is adapted to be vibrated vertically, after the manner that a weight freely suspended on a helical spring may be vibrated. In service sufficient power is applied to the drillrod, to keep the rod and tool assembly incontinuous vibration. Each time that the Vibrating assembly approaches the lower limit of its range powerful operation the expansible andcompressible medium referred to maybe a gas, while in the case of manual operation such medium may with advantage be replaced by mechanical means, such as a spring. r

A manually operable apparatus is illustrated in Fig. I. It consists in a derrick, in this case in the form of a tripod I that rigidly supports a head 2 at an interval above the surface S of the earth in which a bore B is to be drilled. One leg of the tripod is provided with a winch 3, from which a cable may extend, and, trained-over a pulley 4, provide the hoist essential'to the'usual drilling operations. The drill or bit 5 of I the apparatusis secured to the lower end of a toolcarrier 6; the tool-carrier is secured to the lower end of a vertically reciprocable drilling member, which, as stated, may consist in a. tubular drillrod 7; and the drill-rod is in turn secured to the lower end of a feed-screw 8. A helical spring 9 provides the eXpansible and compressible medium or means, upon which the

drill assembly

5, 6, I, 8 is suspended, as mentioned above. The spring 9 is secured at its upper end to the tripod head 2 and at its lower end to a nut-block I Don the feed-screw 8. The spring is adapted to sustain the entire weight of the drill assembly, and such assembly, as so supportedby the spring, is adapted to vibrate on the common vertical axis of the spring and drill-rod. The construction and operation are such that, as the vertically vibrating assembly approaches the lower limit of its range of vibration, the drill does its work; that is, the cutting edges of the drill are 1 driven into the earth or rock at the bottom of the well or bore being drilled. In the continuous vibrationof the drill assembly, the drill repeatedly attacks'and cuts the terrestrial formation at the bottomof the bore. In the course of such operation the drillings or cuttings are removed, the effective length of the drill-rod is increased, and the bore is drilled deeper. ,1 A handle I I is secured upon the drill-rod 1, and

by means of such handle the driller appliessufiiof movement the tool strikes the bottom of the hole being drilled and does its work. As the op eration progresses, the drill-rod is rotated step by step, and with each blow the cutting edges of the tool are caused to strike on diilerent lines. And i as the drilling continues, the effective length of the reciprocating drill-rod is increased, to provide the essential downward feeding of the tool.

The apparatus may be constructed for either manual or p we ful operation. In the case of cient force to maintain the drill assembly in Vibration. In the course of such operation the driller turns the handle and rotates the drill-rod through a succession of slight but suliicientangular intervals, to insure that the cutting edges of the drill will not track. Additionally, it will be understood that the screw 8 rotates in unison with the drill-rod, and that the step-by-step rotation will be in such direction, relatively to the nut, that the screw 8 is fed downward, increasing the effective length of the vertically vibrating drill-rod, and feeding the drill'downward apace with its work. As the depth of the Well reaches the point where the upper end of the screw 8 approaches the nut ID, the operation is intermitted; the handle I I is removed from drill-rod l;

The important thing that has been thus far par-.

ticularly described is the structure by virtue of which vibratory operation of the drill assembly is attained. In this connection it will be understood that the spring (or the other means presently to be described) comprises elastic means that opposes the efiect of gravity on the drillassembly.

When the drill assembly in its vibratory operation moves downward, the spring stores energy that assists the assembly through the next-ensuing upstroke. In this way, the power or effort required to operate the drill is much lower than usual-in some cases the power is one-quarter of that required in the usual drilling apparatus, other things being equal.

The apparatus embodies other features of construction and operation that are important if not essential to the features described above. Turning to the tool-carrier 5, it will be understood that the drill is-yieldingly mounted. It will be perceived in Fig. V that the tool-carrier consists in an extensibleand contractible structure, including two

tubular members

60 and 6| that are telescopically arranged. Organized between such members is a helical spring 62, and such spring is adapted yieldingly to sustain the weight of the tool-carrier member 60 and the bit 5. More specifically, the drill 5 is secured to the lower end of member 60, while the lower end of the drillrod 1 is, by means of a coupling 63, secured to the upper end of member GI. The body of member 60 is of reduced diameter partway of its length and is arranged within the bore of member 6|; integral with member 60 is a casing 64 that terminates at its upper end in a head 65, through which the member BI extends. The member BI is at its lower end provided with a flange 66. The coils of spring 62, housed within casing 64, are arranged externally of the telescoping portions of members 60, BI; and the upper end of the spring is secured against movement under torsional stress'in a hole I62 in the head 65, while the lower end of the spring is made fast to the flange 66. Thus, when the vibrating drill assembly drives the drill against the work (i. e., against thebottom of the bore being drilled), the

members

60, 6| telescopically contract. The spring 62 expands during such contraction of the telescoping members, and the relative movement between such members may in many cases be through such interval that the spring reaches a position of completeexpansion, in which case the upper end of the spring may without harm be drawn from the hole I62. This action of the tool-carrier insures that the drill-rod I will not buckle, and it prevents other parts of the drill assembly from being subjected to harmful strains. When the reciprocating drill-rod rises, the telescopic members 60, SI expand, and, as the weight of the member 60 and bit 5 is suddenly picked up by the rising drill rod, the spring 62 acts'as a shock absorber, gradually applying the weight of such parts to said drill-rod.

It is further to be noted that the spring 62 is a torsion spring, permitting within the limits of spring tension the rotation of member E0 relatively to member 6|. The advantages of the structural refinements described will be appreciated by those familiar with the art, and it is needless unduly to prolong this specification with a consideration of them.

A further feature of invention consists in formduring the drilling operation, and thus it is that Tfa"c0ntinuous sample is available.

In adapting the tool-carrier to this secondary utility, I provide both members 60 and BI in hol- .low or tubular form. The space'within the telescoping members forms an axially extensible and contractible pump chamber C. At the bottom of such chamber, I provide a valve-controlled inlet,

while at the top I provide an outlet communieating with the bore of the drill-rod I. Advantageously, the inlet extends through the body of the drill 5, and opens as close as may be-to its cutting edges 5I- (Fig- V). In this case the drill is of star-drill construction, including four V -shaped. blades 52, backed with plates 53 of relatively hard tool-steel. The said inlet to the pump consists in four passages 5E1, extending one through the body of each of the four blades 52 into a passage 55 that registers with and forms part of the telescopic pump chamber ,0. Checkvalves 58 and 16 are organized in conventional way with the inlet and outlet of the pump.

The operation of the pump will be readily'understood. When the reciprocating or vibrating drill assembly 6, I, 8, drives the tool 5 against the bottom of the bore B, the descent of the lower telescopic member 60 is suddenly arrested, but the upper telescopic member 6 I, together with drill-rod I; continues to descend through, or partway through, the interval between the flange 66 and the, shoulder 67. Then, upon the rise of the drill assembly, the

telescopic members

60, 6| move back into the positions in which they are illustrated. Manifestly, the chamber C within the tool-carrier is alternately extended and contracted, and is effective, with the valves 56, I6. as a pump. Of course, it will be understood that liquid, if it is not naturally present in the well, will be supplied to provide the essential vehicle for the cuttings and other solid particles to be pumped out. The pump forces the material drawn from the bottom of the well upward through the drill-rod I, and delivers it above groundto an outlet coupling [2, that connects the screw 8 to drill-rod I. From such coupling the material isdischarged by way of a spout I3 into a sample-box I4, Fig. 1. (The construction of the outlet coupling I2 will be perfectly intelligible upon considering Fig. IV.)

It is important to note that, contrary to common practice, the liquid supplied to the bore B is introduced externally of the drill-rod, whilethe pump, as said, delivers through the passage within the drill-rod. By virtue of this refinement, a high pneumatic or hydraulic pressure may be established and maintained on the liquid at the bottom of the bore, to assist the pump in its work. Fig. II illustrates that the well or bore B may be provided with a casing, and gas or liquid may be introduced at desired pressure through. a conduit I5. In practice the bore B will be deep and the

parts

5, 6, 63 will normally be far below ground when this pressure-applying operation is practiced, and, of course, in such event the head I5 of the casing will snugly fit the drillrod I, rather than the tool-carrier 6 as shown.

I In case the samples obtained by pumping do not aiford the desired information, a core may be taken from the well. A core-tool may be attached t the tool-carrier 6 in place of the drill the drill-rod I may be positively rotated (without vertical motion) and the core may be cut and removed in usual way.

Figs. II to IV-show the apparatusin' more elaborate form and adapted for powerful operation,

as is essential in the drilling of deep oil-wellsand the like. Save ashereinafter specified, the powerfully operated appara'tusembodies the structural I features of the manuall-y opera'ted structure already described, i i I Whereas in the first structure the'expansible andcompressible means, upon which the

drill assembly

5, 6, I, -8 is suspended for'vertical vibration, comprises a spring, in the power operated machine such means consists in a body of gas, conveniently air, confined in a cylinder ll, beneath a piston l8 connected to the screw -8. This confined body of air operates in general the same as the spring, in providing a yielding support upon which the drill assembly may be vibrated. Above and in axial alignment with the air cylinder I1 I provide a steam'poWe'r cylinder [Sincluding a piston 20 that is" effective in service to keep the drill assembly in vertical vibration.'

The power cylinder is securedatits upper end to a head 2a supported on tripod legs 'lu; the air cylinder I! is secured at its upper end to the lower end of the power cylinder, by means of a cylinder head 21; and the walls of the air cylinder extend below its lower head 22, and are vertically'slotted, as shown at "23, 24, to provide a slide-way 21 for a slide-head structure'25, 26, presently to be described." 'A' hollow piston rod 28, on which are secured the pistons'in both the air and the power cylinders 11 and I9, is at its lower end united to the slide-

head structure

25, 26, and the screw 8 extends upward through such hollow piston. e The slide-

head'structure

25, 26 includes mechanism for effecting the step by-step turning of the reciprocating drill assembly and the feeding of the assembly downward inaccord-with the advance of the drill in its work, but inasmuch as the apparatus of the'invention does not depend upon the particular form of such mechanism, it is needless to describe the same, more than to say:

1. The slide-head member 26 carries a rotary pinion 29a that meshes with a vertical-gear-rack 29 rigidly mounted on slide-way 21; arotary nut (not shown), in threaded engagement with the screw 8, is rotatably secured in the member 26;

during the vertical reciprocation of the drill assembly, the pinion in meshwiththe stationary gear-rack rotates first in one direction and then in the other, and the mechanism within theslideheadstructure operates tofeed the screw 8 down wardasneedbe. 7

2. The slide-head mechanism coordinates the rate of feed with the intensity of impact of the drill 5 against the work. And suchmechanism includes means for indicating on suitable gauges (cf. gauge 30, Fig. II) the intensityof each blow and the depth of cut. i i I Thus, it will be understood that slide-

head structure

25, 26 serves to connect the drill assembly 5, B, 1, 8 withplunger rod 28; that the assembly is yieldingly home and adapted vertically to vibrate on the body of air confined beneath piston IB in cylinder I I; and that the piston 20 in power cylinder lB is energized, to maintain the assembly in vibration. e

I More specifically, the power cylinder l9 includes an exhaust port 3i and a steam inlet port 32 at each-end (Fig. III), and 'in'accordance with good engineering practice each set of ports is controlled bya slide-valve '33 (Fig. II); the slidevalves are organized with a suitable valve-gear 34; and a gear-operating rod 35, secured to and reciprocatingwith the slide-

head

25, 26, operates such valve-gear, alternately to open and close the ports in the power cylinder, in such manner as to effect the continuous reciprocation of the piston 20. Steam is supplied to the valve-controlled inlet ports '32 (Fig. III) from a steam line 36 (Fig. "ID, and theexhaust ports 3| (Fig. III) discharge into an exhaust manifold 31 (Fig. II).

In order that propercoordination of the operating parts-of the apparatus may be established and maintained, I provide means for varying the effective length of that portion of the air cylinder which extends below the piston 18, and I also provide for the regulation of the degree of elasticity of the body of air confined therein. The means 'for varying the effective length of the air cylinder are advantageously hydraulic means, consisting in this case in a hydraulic pump 44 (Fig. III) adapted at the will of the attendant to deliver liquid into a pool P in the bottom of thecylinder, and alternately to remove liquid from such pool. Thus, the depth of thepoolP may be increased or decreased, manifestly achievingthe desired regulation of the effective length of the air cylinder. for regulating the degree of elasticity of the air (withoutnecessarily varying the effective length of the air cylinder) consist in an air compressor 45, communicating through a lead 4| with the air cylinder II, at a point below the piston l8.

- Among-other desiderata this regulation of pneumatic elasticity and pressure permits the establishment of the desired balance between the pressure of air acting upward on the piston is and the force of gravity acting downward on thereciprocable parts.

Another important feature remains for consideration in this specification. It consists in the provision of means for safeguarding the structure in case the drill-rod, or other part, should break and suddenly remove the weight of the drill assembly from the plunger rod 28. Specifically, the power cylinder is provided at each end with a piston 46 secured on a sleeve 41 (Fig. III). I The pistons 46 are arranged respectively above and below the two pairs of ports 3|, 32, and are normally spaced an interval from the ends of the cylinder, as shown.

Pipes

38 and 39 stand in open communication with a source of steam or air under elevated pressure, conveniently the same source of steam (or compressed air) as supplies the power cylinder It. It will be noted that the sleeves 41 carry flanges 48 that severally abut upon the stationary cylinder heads 2!, 8!, and prevent the pistons 46 from moving under steam pressure from the positions in which they are shown. If for any reason the power plunger 28 should travel beyond the normal limits of its range of reciprocation, the

piston 20 will strike either one or the other, as the case may be, of the pistons 46. Manifestly, each piston 46 comprises a yielding cylinder head-a shock absorber-that operates to bring the wild power plunger gradually to rest, without harm to the stationary cylinder heads, or other parts of the apparatus.

In still further accordance with the invention, I organize with the upper end of the air cylinder II a valve-controlled by-pass 40, by virtue The means of .which the upper: end of such cylinder, being normally open to the outer atmosphere, will be automatically closed. if the load 'issuddenly relieved from theplunger rod 28. That is to say, theai-r cylinder is adaptedto 'serveas a pneumatic shock absorber that cooperates with the upper shock-absorbing piston- 46 in the power cylinder Ill. The by-pass 40- communicatesat its opposite ends with the air cylinder at vertically spaced-apart points '93 and 94, and between such points the ,by-pass includes a check valve 98. It is to be noted that both

points

93 and 94 lie, above the upper limit of the normal range of reciprocation of'the piston l8, and that the by-pass includes a branch 9| which, during normal operation of the apparatus, establishes communication between the upper end of the air cylinder and the open atmosphere.

/ If the drill-rod breaks in service, the plunger assembly J8, 20, 28 is by the airpressure beneath piston l8 driven violently upward, carrying th piston I8 above the point 94 at which the by-pass 4G opens into the air cylinder. Immediately, air at exceedingly high pressure fiows from beneath the piston l8 into'the' lower opening 94 -.of theby-pass; the by-pass includes a plunger 92, and'it will be'understood that this air, flowing into the by-pass and surging upward through the check-valve, shoots the plunger 92 upward into a chamber 95 arranged in the bypass structure above the point 93 at which the by-passopensinto the top of the air cylinder l1. With the plunger 92 in such position, the branch 9| is'closed, and a direct line of flow is established from beneath the piston 18 to above, while the check-valve 9ilserves to prevent backsurge from above the piston to below. Thus, a body of air is confined above the piston l8,and

such confined body of air operates to bring-the runaway plunger assembly to rest, without harming the apparatus. The pneumatic pressure thus developed in the upper end of the cylinder may, as the piston l8 approaches the head 2|, exceed the pressure of the air beneath the piston I8, but as already mentioned the check-valve 90 serves to prevent a back-surge of air through theby-pass 40,

The structure described above admits of many modifications within the skill of the engineer, and it will be understood that, within the terms and intent of the appended claims, such modifications lie in the field of the invention.

I claim as my invention:

1. Apparatus for drilling terrestrial bores including two cylinders supported one above the other in axial alignment, a plunger reciprocable in said cylinders, a tubular drill-rod connected to the lower end of said plunger, a tool-carrier connected to the lower end of said drill-rod, a drill secured to the lower end of said tool-carrier, said tool-carrier comprising two tubular members telescopically movable and forming a vertically extensible and contractible pump chamber communicating with the bore of said tubular drill-rod, resilient means arranged between said telescopic members, and a valve-controlled inlet opening from the lower end of said pump chamber through said drill; a piston secured onsaid plunger in the lower of said two cylinders, a body of gas confined in said last cylinder beneath said piston, and. providing a compressible and expansible medium adapted to sustain the weight of the assembled plunger, drill-rod, tool-carrier and drill, means for injecting gas into such body of gas, means for regulating the effective length 2. Apparatus for drilling terrestrial, bores including a vertically extending tubular drill-rod mounted for vertical vibration on a compressible and expansible medium, a vertically extending tool-carrier secured to the lower end of said drillrod, a drill secured to the lower end of said toolcarrier, said tool-carrier including two tubular members telescopically movable relatively to one another andforming a vertically extensible and contractible pump chamber communicating with the bore of said tubular drill-rod, a valve-controlled inlet opening into the bottom of such chamber, and shock-absorbing means arranged between said telescopic members.

3. Apparatus for drilling terrestrial bores including a vertically extending, rotary, tubular drill-rod mounted for vertical vibration on a compressible and expansible medium, a vertically extending tool-carrier secured to the lower end of said drill-rod, a drill secured to the lower end of said tool-carrier, :said tool-carrier including two tubular members telescopically and rotatably movable relatively to one another and forming a vertically extensible and contractible pump chamber communicating with the bore of said tubular drill-rod, a valve-controlled inlet opening into the bottom of such chamber, and a spring arranged between said telescopic members, substantially as described.

4. Apparatus for drilling terrestrial bores including a vertically extending drill-rod mounted for vertical'vibration ona compressible and expansiblemedium, a drill, and-vertically telescoping means securing said drill to the lower end ofsaid drill-rod. 1

5. Apparatus for drilling terrestrial bores including a vertically extending, rotatable drill-rod mounted for vertical vibrationon a compressible and expansible medium, a vertically extending tool-carrier secured to the lower end of said drillrod, a drill secured to the lower end of said toolcarrier, said tool-carrier including two members telescopically movable relatively to one another on the axis of the drill-rod, and shock-absorbing means arranged between said members.

6. Apparatus for drilling terrestrial bores including a vertically extending, rotatable drill-rod mounted for vertical vibration on a compressible and expansible medium, a vertically extending tool-carrier secured to the lower end'of said drillrod, a drill secured to the lower end' of said toolcarrier, said tool-carrier including two members telescopically and rotatably movable relatively to one another, and a compression and torsion spring arranged between said members.

7. Apparatus for drilling terrestrial bores including a vertically extending, rotatable drill-rod mounted for vertical vibration on a compressible and expansible medium, a Vertically extending tool-carrier secured to the lower end of said drill-rod, a drill secured to the lower end of said tool-carrier, said tool-carrier including two tubular members telescopically. movable relatively to one another and forming a: vertically extensible and contractible pump chamber, and a valve-controlled inlet opening into the bottom of such chamber.

8. Apparatus for drilling terrestrial bores including a vertically reciprocable drill'carrier including two telescopic members rotatable relatively to one another, a drill, and a spring arranged between said telescopic members, said spring being responsive to compressive and torsional stresses and yieldingly supporting said drill on the lower end of said carrier.

9. Apparatus for drilling terrestrial bores including a tool-carrier, a vertically reciprocable member extending upward from such tool-carrier, a drill secured to the lower end of said carrier, said carrier comprising two hollow members with an interposed spring, said members being telescopically contractible with the aid of spring tension when said drill is driven downward against the work and telescopically extensible against the opposition of spring tension when (under the pull of said reciprocable member) said drill is lifted from the work, and a valvecontrolled inlet in the bottom of such hollow toolcarrier, whereby said carrier provides a continuously operating pump during the well-drilling reciprocation of said member.

10. Apparatus for drilling terrestrial bores including a vertically extending, rotary, tubular drill-rod mounted for vertical vibration on a compressible and expansible medium, a reciprocating engine having a piston rod connected to the upper end of said drill-rod, said engine providing energy to maintain said drill-rod in vibration, a vertically extending tool-carrier secured to the lower end of said drill-rod, a drill secured to the lower end of said tool-carrier, said tool-carrier including two tubular members telescopically movable and forming a vertically extensible and contractible pump chamber communicating with the bore of said tubular drill-rod, means for yieldingly resisting and assisting such telescopic movement of said members, and a valve-controlled inlet opening from the lower end of said pump chamber through said drill.

11. Apparatus for drilling terrestrial bores including a vertically extending drill-rod carrying a drill at its lower end, a plunger connected to the upper end of said drill-rod, a power cylinder, said plunger carrying a power piston reciprocable in said cylinder for axially vibrating said plunger and drill-rod assembly, and means for protecting the apparatus from damage in case the drill-rod should break in service, said means including a bumper piston positioned in the upper end of said power cylinder above the upper limit of the normal range of reciprocation of said power piston, and a body of fluid confined above said shock-absorbing piston.

12. Apparatus for drilling terrestrial bores including a vertically extending drill-rod carrying a drill at its lower end, a plunger connected to the upper end of said drill-rod, a power cylinder, said plunger carrying a power piston reciprocable for axially vibrating said plunger and drill-rod assembly, said power cylinder including a stationary cylinder head at each end, a shock-absorbing piston secured in each end of said cylinder, said shook-absorbing pistons being spaced from the respective heads of said'cylinder in positions beyond the respective limits of the range of reciprocation of said power piston and a body of fluid confined in the cylinder between each shock-absorbing piston and the companion cylinder head.

13. Apparatus for drilling terrestrial bores including a cylinder, a piston in such cylinder, a body of gas confined in said cylinder beneath said piston, a drill assembly connected to said piston, with the weight of said assembly borne by the body of gas beneath the piston, a body of liquid confined in said cylinder beneath the body of gas therein, and means for varying the depth of said body of liquid, to regulate the effective length of the portion of said cylinder extending below said piston.

14. Apparatus for drilling terrestrial bores including a cylinder, a piston in such cylinder, a body of gas confined in said cylinder beneath said piston, a drill assembly connected to said piston, with the weight of said assembly borne by the body of gas beneath the piston, and means for injecting gas into such body, a body of liquid confined in said cylinder beneath the body of gas therein, and means for varying the depth of said body of liquid, to regulate the effective length of the portion of said cylinder extending below said piston.

15. Apparatus for drilling terrestrial bores including a drill-rod supported at the earths surface for vertical reciprocation, said drill-rod adapted to extend downward from the earths surface into the bore being drilled, a drilling tool,

means yieldingly supporting said tool upon the end of said drill-rod at the bottom of such bore, and means at the top of such bore opposing the efiect of gravity on the drill-rod and tool assembly, said last means being adapted to store energy during the downstroke of the drill-rod and tool to assist in the ensuing upstroke thereof.

16. Apparatus for drilling terrestrial bores including a drill-rod supported at the earths surface for vertical reciprocation, said drill-rod adapted to extend downward from the earths surface into the bore being drilled, a drilling tool, means yieldingly supporting said tool upon the end of said drill-rod at the bottom of such bore, and an elastic body of compressed gas confined against flow at the top of such bore and sustaining the weight of said drill-rod and tool assembly, said body of air being adapted to store energy during the downstroke of the said assembly to assist in the ensuing upstroke thereof.

17. Apparatus for drilling terrestrial bores including a cylinder, a piston in such cylinder, a body of gas confined in said cylinder beneath said piston, a drill assembly connected to said piston, with the weight of said assembly borne by the body of gas beneath the piston, the portion of said cylinder above said piston normally communicating with the open atmosphere, and valve means for automatically interrupting such communication, whereby a body of air is confined above the piston, yieldingly to arrest such piston when it moves above the upper limit of its normal range or" movement, said valve means comprising a by-pass communicating with said cylinder at vertically spaced apart points above said normal range of piston movement, said by-pass including a check-valve, an outlet opening to the outer atmosphere above said check-valve, and a movable member for closing said outlet in the event that said piston rises above the lower point at which said by-pass communicates with said cylinder.

WILLIAM R. COLEMAN.