US3190372A

US3190372A - Methods and apparatus for drilling bore holes

Info

Publication number: US3190372A
Application number: US177623A
Authority: US
Inventors: Ford L Johnson
Original assignee: Sun Oil Co
Current assignee: Sunoco Inc
Priority date: 1962-03-05
Filing date: 1962-03-05
Publication date: 1965-06-22
Anticipated expiration: 1982-06-22

Description

June 22, 1965 F. L. JOHNSON 3,190,372

METHODS AND APPARATUS FOR DRILLING BORE HOLES Filed March 5, 1962 2 Sheets-Sheet 1 INVENTOR. FIG. L FORD L. JOHNSON ATTOR June 22, 1965 L. JOHNSON METHODS AND APPARATUS FOR DRILLING BORE HOLES Filed March 5, 1962 2 Sheets-Sheet 2 7 N J 00 JH T .N W ,m H N m 05 I (H4 L D N R W m l a w w. B8 B o m m o 3 6 4 AD -w /A A /7n 6 M n e United States Patent 3,190,372 METHODS AND APPARATUS FGR DRILLING BORE HQLES Ford L. Johnson, Newtown qnare, Pa, assignor to Sun M Company, Philadelphia, Pa, a corporation of New ersey Filed Mar. 5, 1962, Ser. No. 177,623 "5 Claims. (Cl. 175--2) This invention relates to new and improved methods and apparatus for utilizing explosive materials as auxiliary tools to assist conventional drillbits in more rapidly progressing through particularly hard strata.

As described in my copending application Serial No. 86,077, now Patent No. 3,130,797, filed January 31, 1961, shaped charges may be dropped through a hollow drill stem and projected through the jet openings in conventional roller or other type bits to eilect shattering of rock to facilitate drilling. However, the use of such single charges can be considerably improved, in the way of shattering rock, by the addition of a secondary charge which is not of the shaped type, but rather one which produces a spherical shock front. The present invention utilizes a forwardly directed shaped charge which func-' tions to blast an elongated hole extending below the drill bit and further includes a second explosive charge which is driven into this hole and detonated therein so that a greatly increased volume of rock is shattered, whereupon, conventional drilling may then proceed through this shattered portion. In this regard, it should be emphasized that the primary purpose of the invention in using explosives is not to form the final bore hole, but rather, to break up the hard strata so as to allow more rapid advancement of the conventional bit as well as to save wear on the bit which otherwise becomes dulled in attempting to penetrate this type of hard formation.

In the preferred form of the invention, conventional bits are used, and the explosive members are projected into or through one or more openings which, between explosions function as usual mud openings and preferably as jet openings, the most eliective bits at the present time being of the jet type. Because itis the shattering effect which is desired, it is not required that the explosions should necessarily be directed along the axis of the bore hole, but, rather, the major explosive energy may be directed along the axes of conventional jet openings which are at acute angles relative to the drill stem axis.

While reference has been primarily made to conventional drilling by means of a rotary drill stem driving a bit, it will become evident hereafter that the invention is applicable to hammer drills in which flow of fluid (mud) under pressure is utilized to eifect a hammering action on the rock, or to turbo drills in which a rotary bit at the bottom of a drill stem is driven by a mud turbine while the major portion of the drill stern remains stationary and serves merely as a mud conduit and support.

In summary of the advantages of the invention it may be pointed out particularly that throughout the drilling of a complete hole the same drilling apparatus may be used with its action augmented only where that is required by reason of hard rock formations. When these are encountered explosions may be effected as indicated above while the drilling proceeds without interruption. There is no need for removing the drill stem, nor is there generally any need even for raising the drill stem from its active drilling position. No special apparatus is required for taking care of debris since, even if as the result of the explosions large sections of rock are initially produced these are ground up by the operation of the drill bit and thus become fine enough to be removed by the mud flow in completely conventional fashion. As will hereafter appear more clearly, the mud flow is also utilized to effect positioning and firing of the explosive members.

It is the general object of the present invention to provide new and improved methods and apparatus for utilizing multi-charge explosives as auxiliary tools in conjunction with conventional drill bits and, most particularly, with cone type bits. More detailed objects will become apparent from the following description when read in conjunction with the accompanying drawings, in which:

FIGURE 1 is a diagrammatic illustration showing the upper portion of a conventional drilling rig in association with means for inserting explosive elements in the mud flow stream;

FIGURE 2 is an enlarged showing of a conventional cone type drill bit suitably modified for practicing the invention;

FIGURE 3 is an illustration of a first form of a multiple charge element hereinafter referred to as a torpedo;

FlGURE 4 is a sectional view of the torpedo taken along the plane indicated by line 4-4 in FIGURE 3;

FIGURE 5 is an illustration of a second form of multiple charge torpedo; and

FIGURE 6 is an illustration of an alternative firing mechanism.

FEGURES 1 and 2 show, merely as an example, a drilling rig which is substantially conventional and which can be used for the practice of the invention. Many other drilling rigs may be used which may also be substantially conventional, involving only minor changes for practice of the invention.

There is indicated at 2 a hook which is connected to the usual travelling block supported by cables and controlled by the drawworks of a derrick (not shown). A bail 4 hung on the hook supports the conventional swivel 6 modified only to the extent that its drilling mud entrance opens upwardly and its interior is provided with means for guiding the explosive members as will be evident hereafter. The swivel is joined at S with the usual kelly 10 passing through the rotary table 12 by which it is driven and supporting the sectional drill stem 14 in conventional fashion. The drill stem terminates in the usual drill collar 18. Various conventional parts of the assembly are not indicated, but it will be understood that they are provided as in usual drilling practices.

The drill collar 18 carries a bit 29 which is illustrated as of the multiple cone type, of which one of the cones is indicated at 22. Jet openings are provided directed between the cones, these being provided at 26 through liners 24 for resisting abrasion by the mud. In the present instance one of these jet openings is modified in that its liner 23 is extended upwardly to provide a guiding funnel 39 which is adapted to guide the explosive members through the opening. The funnel 30 is spaced from the walls of the central upper opening in the bit so that mud may flow not only through the liner 28 but from the annular space 3% about the funnel through the other jet openings 26. To provide for free flow of the mud to the space at 34 there may be provided slots in the lower portion of the drill collar as indicated at 32, the arrangement being such that all of the jet openings receive adequate supplies of mud to provide high velocity jets during drilling in conventional fashion. The hole being drilled is indicated at 16.

The mud flows to the swivel 6 through the flexible hose 36, being supplied from the usual high pressure mud pump which is not shown. The main fiow takes place through a connection 46, but bypassed fiow to'carry the torpedoes into the hose 36, swivel 6, and the hollow drill stem takes place through a suitable loading mechanism indicated by numeral 38. Since any number of various mechanisms may be employed to insert the torpedoes in the mud flow pipe 36 and since the details thereof form no part of the present invention, a full description thereof is not necessary. However, reference may be made to my aforementioned application wherein the details of such a mechanism are fully described. Briefly stated, such a mechanism includes a barrel similar to that employed in a revolver so that the torpedoes contained within the barrel successively are aligned with branch conduit 42 and thereby propelled by the mud through conduit 36 and into and through the drill stem.

Reference is now made to FIGURE 3 which illustrates a first form of torpedo for practicing the invention. In general, the torpedo consists of a casing 44 which may be described as having six sections 46-56 all or some of which may be integral or provided with interengaging means such as threaded portions. It should also be noted that each of these sections may be composed of metal or shock resistant plastic so long as they are capable of protecting the explosive material and the firing means from the mud, incidental shocks and the pressures existing in the bore hole. Similarly, a wide latitude of thicknesses are possible so long as the casing performs its protective function. The casing, however, should be such as to break up into small fragments as successive explosions occur, and for this purpose may be grooved in the conventional fashion of hand grenades.

Nose section 46 contains a centrally positioned cap 58 which is frangible upon impact against the bottom of the bore hole, which input will be quite large due to the high velocity of mud flow. For example, cap 58 may be composed of a ceramic material and have a sufficient thickness to withstand the shocks occurring in handling and during its descent through the drill stem. However, cap 58 is sufiiciently frangible to be shattered upon impact with the hard rock forming the bottom of the bore hole. It should also be noted that since the torpedo does not have a substantial velocity relative to the mud, but rather, is entrained and carried by the mud flow, the hydrodynamic shape of nose section 46 is not critical. As a result, the nose section may be relatively blunt so that cap 58 is protected from striking funnel 3t) regardless of the angular position of the torpedo as it approaches funnel 3t In order to control the orientation of the torpedo at this time, a relatively long tail section 56 is provided so that the torpedo maintains a substantially vertical or axial position during its descent. Since the maximum angle of derivation from the vertical can be determined by the length of the tail, the shape of the nose section 46 as well as the curvature of funnel 350 may be designed to positively prevent cap 53 from contact with the funnel.

As further shown in FIGURE 3, cap 53 receives end 69 of a rigid firing pin 62, the pin extending centrally through

sections

46, 48, th, 52 and 54. Since a single firing pin is utilized to detonate all of the charges as well as the propellant, as will be more fully described hereinafter, a safety pin 64 may be passed through nose section 46 and pin 62 so that it positively prevents accidental movement of the firing pin prior to the insertion of the torpedo in the loading mechanism at which time the safety pin may be removed and the torpedo becomes semiarmed.

Immcdiately above nose section 46 there is located a shaped charge 66 which is confined at the forward end by a conical retainer 68. As is well known in the art of shaped explosives, retainer 68 may be in one of various forms each form being particularly designed to create a cavity of a particular shape. In this regard, the major requirement is that shaped charge 66 be designed so as to create a cavity having a depth and a diameter sufficiently large to permit the entry of high explosive section 52. In addition, it is of course desirable to produce a cavity having a depth greater than the length of section 52 in order to achieve a maximum amount of shattering upon detonation of section With these parameters in mind, charge 66 may be designed so that the angle of cone 68,

the stand-off distance between the apex of cone 68 and the tip of cap 53 and the location of the detonator 74 are suitable for achieving these objectives.

A detonator 7d is provided in the form of a cap which threadedly engages cylinder portion 72 of cone 68. Firing pin a2 is provided with an enlarged head 74 which is located in detonator 7t) and positioned at the lower end thereof, the remaining portion of the detonator being filled with an impact-sensitive detonation material which is fired upon movement of head 74. The upper end of charge 66 is enclosed by a pair of relatively

thick diaphragms

76, 78 between which there is provided a highly shock absorbing material 80, For example, this may be a plastic foam material containing sealed air pockets which disrupt the shock front and impede the velocity of portions thereof so that destructive interference effectively destroys the shock wave in the upward direction. Of course, it should also be noted that the amount of shock absorbing material and the thickness of

diaphragms

76 and 78 is directly proportional to the efficiency of shaped charge 66. In this type of charge it is actually possible to have substantially all of the explosive force directed forwardly, downwardly as viewed in FIGURE 2, so that a very minimum of such shock absorbing means are necessary to protect the high explosive section 52. That is, so long as the explosive within section 52 is of the non-impact type, the detonation of the shaped charge may be safely accomplished without detonation of the high explosive.

Diaphragm 73 performs the additional function of cooperating with diaphragm 82 and easing section to provide a housing for a secondary safety mechanism 84. This mechanism includes a piston 86 the outer end of which is exposed to the well fluids and the inner end of which is biased outwardly by spring 88. Piston is provided with an elongated slot 90 through which firing pin 62 passes. However, the firing pin is provided with a radially extending lug 92 immediately below piston 86 so that, when the piston is biased to its rightmost position as illustrated in FIGURE 3, lug 92 is prevented from moving upwardly through slot 90. On the other hand, when the torpedo has descended to a depth wherein the pressure of the well fluid is sufiiciently high to displace piston 86 to the left against the preset biasing force of spring 88, lug 92 is then unlocked and the torpedo is fully armed. Thus, safety mechanism 84 performs the very desirable function of positively preventing detonation until the torpedo has proceeded a safe distance from operating personnel at the surface even though the primary safety pin 64 has been removed prior to its descent.

Immediately above safety mechanism 84- there is positioned the high explosive section 52 which is enclosed at its lower end by diaphragm 82 and at its upper end by diaphragm 94 both of which may be integral with casing section 52. A cylinder 96 is provided with one end threadedly engaged in diaphragm 32 and its upper end threaded for the reception of detonator casing 98 thereby rigidly securing the latter in position. Detonator 9-8 is surrounded by .a suitable high explosive material such as TNT or the like which is not impact-sensitive so that it is not detonated upon the detonation of shaped charge 66. In order to provide for the delayed detonation of section 52, detonator 98 includes a layer consisting of a small amount of impact-sensitive ignition material 160 surrounding the enlarged head 102 of firing pin 62. A suitable delay train tiltof slow burning powder is provided immediately above ignition material and, in turn, a main detonator material 1% is positioned immediately above the delay train. Casing 98 is designed so that the high explosive is not detonated upon ignition of igniter material 16-6, but rather, is only detonated upon the ignition of detonator material 1% as is conventional in such explosive primers.

Immediately above high explosive section 52 there is provided a propellant section 54 containing a suitable propellant material Kid. The propellant 133 is slower-burning than the very high burning rate shaped charge explosive material, so that, even though simultaneously ignited, time delay occurs as brought out later. Since it is necessary that casing 54 contain the propellant after its ignition and throughout its burning period, it should be noted that casing 54 is relatively thicker than the casing sections housing the explosive charges. It will also be noted that the interior surface of casing 54 may be formed as a reaction nozzle 109 of the convergent-divergent type in order to obtain maximum thrust from the propellant. Means for igniting the propellant are provided in the form of a cup-shaped member 110 supported by a web 112 secured to the inner surface of the-nozzle. Cup 1-10 contains ignition material 1 14 of the impact-sensitive type so that propellant 108 is ignited upon upward movement of firing pin 62. It will be readily understood that cup 110 and web 112 are of light construction since they only serve to contain ignition material 114 prior to detonation. Thereafter, they are disintegrated by the intense heat of the burning front of the propellant and discharged outwardly through the nozzle along with the other propella-nt products.

Reference is now made to the aft section 56 which is composed of a rubber, aluminum, or other lightweight casing which may be provided with a central cavity 116 filled with air or other inert gas. The purpose of this aft or tail section is to guide the torpedo through the drill stern and prevent it from assuming an angular position relative to the vertical axis of the drill stem whereby it might engage funnel 30 and cause a detonation within the drill bit. Tail 56 is preferably made as buoyant as possible so that the torpedo remains in a vertical position throughout its descent through the stem and therefore becomes readily entrained in the mud flowing through the stem and jet 28. In addition, the tail portion serves as a piston or plunger when the torpedo has assumed the position shown in FIGURE 2 wherein the high pressure fluid acts upon the end of tail 56 and forces cap 58 against the bottom of the bore hole with considerable force and velocity so that detonation is assured.

Lastly, it will be noted that the mutually engaging ends of

sections

52, 54 and 56 are provided with threaded

portions

118 and 120, respectively. Similarly, firing pin 62 is provided with a separable section 1-22 which is threaded to the lower portion of the firing pin so that propulsion section 54 may be removed and tail section 56 may be threaded to the aft end of section 52. For this reason, section 56 is provided with a slot 124 so that, in the event propulsion section 54 is not employed, the aft end of firing pin 62 will terminate in cavity 124. Thus, the torpedo is designed for use with or without propulsion section 54- the reason for which will be more fully set forth in the description of operation,

Ordinarily, the drilling through relatively soft formations will proceed in the usual fashion without the aid of explosives and the use of the present method does not involve any deviations from the normal practice employed in rotary drilling wherein conventional, cone-type bits are utilized for the most rapid rate of drilling progress. The jet openings in the bit perform their normal function of assisting the rollers by flushing the cuttings and also by the jet action of the mud flow which tends to assist the bit in cutting the well bore. Insofar as the structure of the drilling rig is concerned, the only matter which need be taken into account in the practice of the invention is that the mud hose should have a sufiiciently large radius of curvature so that it does not impede the free movement of the torpedoes therethrough when they are used. Thus, ordinarily the major portions of the of drilling is slowed down by the encountering of hard strata. This will be evidenced quite promptly by observation of the downward movementof the drill stem. When this occurs, safety pin 64 is removed from one of the torpedoes and the torpedo is introduced into the mud line by the means of the loading mechanism 38. During the period of introduction of the torpedo and the time of its descent to the location of the bit, drilling may be continued, continuation having no adverse effect with reset to the explosive operation.

The torpedoes may range from substantially heavier to substantially lighter than the mud depending upon the buoyancy of tail 54, however, it is preferable to have the torpedos as a whole somewhat heavier than the displaced mud in order to speed their rate of descent. Actually, the speed of descent in either case will approximate rather closely the rate of mud flow. Accordingly, the torpedo becomes entrained in the mud flow and the buoyancy of tail section 54 relative to the forward portions of the torpedo will tend to keep it axially aligned and prevent any violent engagement with the internal surface of the drill stem through which it passes as at the drill stem joints. However, the torpedo may glance off the internal surface of the drill stem without any possibility of exploding. Arming occurs, when a suificient pressure is encountered, by the inward movement of piston 84. As previously indicated, the entire casing structure is sufficiently strong to resist the pressure increase and is also sufiiciently strong to withstand the above-mentioned glancing impacts. Thus, the firing pin remains unmoved during the descent and, as also stated hereinabove, the location of cap 53 and the relatively blunt shape of nose section 46 prevent firing of the torpedo by impact with funnel 130. The torpedo passes through the funnel, being guided thereby, and enters the jet opening defined by liner 28. Since the mud flow is continuing, the velocity of the torpedo will be increased as it passes through the jet opening and it will be ejected at an extremely high velocity so that there is virtually no possibility that cap 58 will not be shattered upon impact with the rock strata at which time firing pin 62 is forced upwardly relative to the torpedo casing.

. At this point it must be noted that the following events occur simultaneously from a macroscopic view point, however; in order to understand the operation of the invention, it is necessary to describe the events in a greatly exaggerated degree of slow motion, the actual time intervals between various events being measured in milliseconds. First, it will be appreciated that the torpedo as a unit has considerable momentum at the instant of impact between the forward end of cap 58 and the rock strata. Thus, firing pin 62 is driven rearwardly relative to the casing which continues in the forward direction. Secondly, it will also be noted that tail portion 54 is contained within liner 23 at the instant of impact so that the torpedo acts as a plug in the jet opening of the bit having considerable pressure exerted by the mud on its tail portion which further aids the propulsion of the torpedo. Thirdly, the dimensions of the firing pin are chosen such that pin 62 extends forwardly beyond the edge of nose 46 for a distance which is considerably greater than the amount of displacement of the pin which is necessary to detonate the detonators 7t 1% and This design, although not absolutely necessary, greatly increases the resultant effect by allowing shaped charge 66 to explode and create the necessary cavity in the rock strata while the remainder of the torpedo still retains considerable momentum and is therefore more easily driven into the cavity formed by the shaped charge.

Referring again to the instant of impact, it will be noted that all three detonators are simultaneously fired so that propulsion section 54 is ignited at the same time that shaped charge 66 is detonated. However, because of its slower burning rate'the propellant exercises its driving effect only after the action of the shaped charge has been completed. Ignition of the propellant immediately separates the forward portion of the torpedo from tail portion 56 which is connected th reto by the relatively weak connection provided by threads 126 At this point it should also be understood that propellant section 54 may or may not be employed depending upon various factors including the depth at which the bit is operating and the amount of explosive material utilized in charge es. if the depth is sufficiently great so that an extremely high pressure of the mud is exerted against tail section 56, this may be sutficicnt to drive the high explosive section 52 into the cavity formed by the shaped charge, the latter being sufiiciently small and accurately designed so that substantially the entire force is directed forwardly to shatter the rock and very little energy is left to react upon the remaining portion of the torpedo. in either event, high explosive section is driven into the cavity formed by shaped charge so and the high explosive section explodes after it is located therein. This is accomplished by means of the interposition of delay train 164 between ignition material 1% and detonator material 1%.

As previously stated, the time period between detonation of the shaped charge and the high explosive section may be in the order of thousandths of a second so that delay train Mid may have a very short delay time.

From the foregoing escription it will be apparent that the present invention provides a marked divergence from what is described in ray copending application in that the purpose of shaped charge so is to create a hole for the reception of the high explosive section, the latter performing the actual shattering of the rock whereby the progress of the drill bit is substantially increased over the result previously obtained by utilizing the shaped charge alone as the rocl: shattering explosive.

It may be noted that because the action of the shaped charge in forming a hole is followed by the driving of the high explosive into the hole by a matter of only milliseconds, even though the at is continuously rotating there is maintained, for all practical purposes alignment of the jet opening with the formed hole during the sequence of explosive events.

Reference is now made to FEGURE 5 which illustrates a second form of multiple charge torpedo for practicing the invention. This form differs from that previously described in that it employs an electrical firing system rather than the mechanical impact type just described. This embodiment employs an electrically conductive casing I139 having a nose section 7.32 which threadedly receives an electrically conductive cylinder 134. A firin: plunger res which is also composed of an electrically conductive material is received within cylinder f 3 and may be provided with an O-ring seal to prevent the entrance of well fluids. A safety pin is received in cylinder 134 and passes through plunger 136 in order to prevent accidental displac ment of the plunger prior to its entrance into the loading mechanism The upper or rearward end of plunger 136 is formed of a reduced diameter and surrounded by a snap action spring the periphery of which is engaged in an annular roove in cylinder 134. Immediately above the plunger there is elongated electrode 142 the lower end of which is spaced from the upper tip of the plunger thereby forming a snap action switch as will be more fully explained hereinafter. The upper end of electrode 142 is secured to cone 144 which forms a conical retaining wall for the explosive material 146 comprising the shaped charge 143. This charge further includes a detonator lS-tl which comprises a casing 1513 containing suitable detonation material and two spaced electrodes -1, 156 joined by a filament E58. Electrode 154- is connected to liner and electrode 142 by means of a suitably insulated lead 16% passin through the explosive material 146. It will be noted that liner 144 is insulated from casing 13%? by the interposition of insulator ring M5. Electrode 56 is connected by an insulated lead 162 to contact 171 located in diaphragm 16$ but insulated therefrom. A capacitor Lid is insertable in bore 165 and are adapted to be sealed therein by plate 101:. Capacitor 164 is provided with an insulating casing 176) having exposed terminals i713 and 174- which connect the plates of the capacitor to

contacts

172 and 176, respectively. Contact 176 is positioned in diaphragm but is suitably insulated therefrom. In turn, contact 176 bears against the surface of pressure responsive piston 132 which includes a radially inner portion composed of an insulating material and a radially outer portion 1% composed of an electrically conductive material. Upon increase of pressure in the Well as the torpedo descends, conductive portion 186

bridges contacts

176 and 18 3 thereby establishing a circuit from lead 162 to lead 188. Thus, this mechanism serves the same function as that of mechanism 84 previously described.

High explosive section M9 is positioned immediately above the safety mechanism and consists of a suitably sized charge 192 of a non-impact type explosive material surrounding a three part detonator 194. Detonator 194 is identical to detonator 93 previously'described except for the substitution of

electrodes

185, 187 and filament 189 in place of the mechanical firing pin. Detonator 94 provides the desired time interval between detonation of charges 14% and 192 by reason of delay train 1% which functions in a manner identical to delay train 134 as previously described.

Above the hi h explosive section there is provided a propulsion section 1% containing propellant 199. This section is identical to propulsion section 54 previously described except for the substitution of electrodes 294), 2% and filament 264 in place of mechanical firing pin 62. It will be noted that electrode 202. is connected to casing which thereby completes the circuit back to plunger 136.

The operation of this embodiment is as follows. Capacitor 164 is charged and inserted into the circuit wherein it is retained by cover plate 168 just prior to use. Upon engagement or" plunger 136 with electrode 142, capacitor 164 discharges causing filaments 153, 189 and 294 to simultaneously ignite their respective detonators. This causes simultaneous detonation of charge 148 and ignition of propellant 199 so that a cavity is produced into which charge 192 is propelled and exploded.

It will also be noted that this embodiment provides for the removability of propulsion section 198 and the alternative connection of tail section 208 to the upper end of the high explosive section by reason of threaded

portions

210 and 212. Thus, the employment of this embodiment is identical to that previously described and the operation thereof produces the same high degree of rock shattering as does the first embodiment.

Reference is now made to FIGURE 6 which illustrates a magnetically responsive actuating system which may be employed in place of or in addition to the impact type actuating means 58 and 136 or FIGURES 3 and 5, respectively. FIGURE 6 illustrates the same condition as illustrated in FIGURE 1 wherein tail section 298 of the torpedo is within liner 28 at the instant of impact with the bottom of the bore hole. In this embodiment, a plurality of permanent magnets 22% are circumferentially disposed in the Walls of liner An additional permanent magnet 222 is pivotally supported by shaft 224 and biased into a position perpendicular to the longitudinal axis of tail section 2-03 by means of tension springs 226 secured to diaphragm 2Z8. Magnet 222 therefore remains in this position irrespective of axially or radially directed impacts occurring during the descent of the torpedo. Iowever, when the torpedo is positioned such that the poles of magnet 222 are centered between the poles of magnets 22%, the four magnetic forces of repulsion and attraction become additive so that magnet 222 is forcibly rocked about piVOt shaft 224- in the direction of the arrow shown in FIGURE 6. This movement is communicated to rod 239 which may be secured to magnet 222 or shaft 224 and the movement of rod 236 may be utilized to close the firing circuit of the FIGURE 5 embodiment or to mechanically actuate firing pin 62 of the FIGURE 1 embodiment. If

utilized with the latter embodiment, a compression spring may be inserted between end 60 of firing pin 62 and cap 58 and rod 230 may be connected through suitable linkage to remove an additional pin operating in the nature of pin 64 to release firing pin 62.

Since numerous modifications and/ or alterations will become readily apparent, it is to be understood that the foregoing embodiments are intended to be illustrative rather than exhaustive and that the invention is not to be limited otherwise than as set forth in the following claims.

What is claimed is:

1. The method of drilling a bore hole through earth strata comprising the steps of:

effecting rotary drilling with a hollow drill stem driving a drill bit having a solid central portion and a nonaxially aligned jet opening to form a bore hole of a first depth,

introducing a multiple charge torpedo into said hollow drill stem at the surface of the bore hole,

effecting axial passage of said torpedo downwardly through said hollow drill stem to the vicinity of said bit,

orienting said torpedo so as to pass at least partially through said non-axial jet opening to arrive at a position adjacent the earth strata forming the bottom of said bore hole,

detonating a first charge of said multiple charge torpedo to form a cavity in said strata forming the bottom of said bore hole,

explosively propelling a second charge of said multiple charge torpedo into said cavity,

detonating said second charge to eifect fracturing of the material forming said cavity, and

continuing rotary drilling through said strata by said drill bit.

2. The method of drilling a bore hole through earth strata comprising the steps of:

entraining said torpedo in flow of drilling fluid to pro pel it at least partially through said jet opening to arrive at a position adjacent the earth strata forming the bottom of said bore hole,

detonating said second charge to etfect fracturing of the material forming said cavity, and

continuing rotary drilling through said strata by said drill bit.

3. Apparatus for drilling a bore hole comprising in combination:

mechanical drilling means,

said drilling means including a drill stern and a drill bit secured to the lower end of said stem,

an axially extending passage in said drill stem,

at least one jet opening extending through said bit in a 10 direction transverse to said drill stern passage and in fluid communication therewith, a multiple-charge torpedo of a size sufficiently small to pass through said passage and said jet opening,

guiding means within said drilling means for effecting .the passage of said torpedo from said passage into said transverse jet opening and at least partially through said jet opening to a position adjacent the bottom of the bore hole,

means for detonating a first charge of said multiplecharge torpedo to form a cavity in the bottom of said bore hole,

explosive means for eifecting the entrance of a second charge of said multiple-charge torpedo into said cavity, and

means for detonating said second charge to produce explosive shattering of the material surrounding said cavity.

4. The apparatus as claimed in claim 3 wherein the said first charge is a shaped charge.

5. Apparatus for drilling a bore hole comprising in combination:

mechanical drilling means,

an axially extending passage in said drill stem,

at least one jet opening extending through said bit in a direction transverse to said drill stern passage and in fluid communication therewith,

a multiple-charge torpedo of a size sufiiciently small to pass through said passage and said jet opening,

guiding means within said drilling means for eifecting the passage of said torpedo from said passage into said transverse jet opening and at least partially through said jet opening to a position adjacent the bottom of the bore hole,

means for maintaining said torpedo in a substantially vertical position during the descent thereof through said drill stem passage,

explosive means for effecting the entrance of a second charge of said multiple-charge torpedo into said cavity, and

References Cited by the Examiner UNITED STATES PATENTS 1,511,488 10/24 Alexander 102-20 1,585,664 5/26 Gilman -2 2,307,729 1/43 Foster 175-2 2,416,077 2/47 Yuster 102-20 2,809,585 10/57 Moses. 2,869,825 1/59 Crawford. 2,898,085 8/59 Borins et al. 175-2 2,910,000 10/59 Brandt 102-56 3,047,796 7/62 Bennett et al. 175-50 3,070,010 12/62 Robinson 175-2 3,083,778 4/63 Friedman et al. 175-2 CHARLES E. OCONNELL, Primary Examiner,

Claims

1. THE METHOD OF DRILLING A BORE HOLE THROUGH EARTH STRATA COMPRISING THE STEPS OF: EFFECTING ROTARY DRILLING WITH A HOLLOW DRILL STEM DRIVING A DRILL BIT HAVING A SOLID CENTRAL PORTION AND A NONAXIALLY ALIGNED JET OPENING TO FORM A BORE HOLE OF A FIRST DEPTH, INTRODUCING A MULTIPLE CHARGE TORPEDO INTO SAID HOLLOW DRILL STEM AT THE SURFACE OF THE BORE HOLE, EFFECTING AXIAL PASSAGE OF SAID TORPEDO DOWNWARDLY THROUGH SAID HOLLOW DRILL STEM TO THE VICINITY OF SAID BIT, ORIENTING SAID TORPEDO SO AS TO PASS AT LEAST PARTIALLY THROUGH SAID NON-AXIAL JET OPENING TO ARRIVE AT A POSITION ADJACENT THE EARTH STRATA FORMING THE BOTTOM OF SAID BORE HOLE, DETONATING A FIRST CHARGE OF SAID MULTIPLE CHARGE TORPEDO TO FORM A CAVITY IN SAID STRATA FORMING THE BOTTOM OF SAID BORE HOLE, EXPLOSIVELY PROPELLING A SECOND CHARGE OF SAID MULTIPLE CHARGE TORPEDO INTO SAID CAVITY, DETONATING SAID SECOND CHARGE TO EFFECT FRACTURING OF THE MATERIAL FORMING SAID CAVITY, AND CONTINUING ROTARY DRILLING THROUGH SAID STRATA BY SAID DRILL BIT.