AU3134700A - Directional drilling system for hard rock - Google Patents

Description

WO 00/55468 PCT/AU00/00183 DIRECTIONAL DRILLING SYSTEM FOR HARD ROCK TECHNICAL FIELD OF THE INVENTION The present invention relates in general to an arrangement of a bottom hole assembly where boreholes can be drilled in a directionally controllable manner, utilizing existing down-hole hammer drills. More particularly, the present invention pertains to apparatus for providing directionally controlled boreholes in hard rock. RELATED APPLICATION This application claims the benefit of pending U.S. provisional patent application filed March 15, 1999, Serial No. 60/124,470, and entitled DIRECTIONAL DRILLING SYSTEM FOR HARD ROCK, the entire subject matter of which is incorporated herein by reference.

WO 00/55468 PCT/AU00/00183 2 BACKGROUND OF THE INVENTION The practical need to adjust the trajectory of a borehole in the earth comes from several requirements. Most boreholes are designed to be straight, but in practice are not. Many prior boring techniques would benefit from some system that maintains the boreholes straight. It is often desirable to change the directions of boreholes to pass through a known target that is not in line with a straight trajectory of the borehole. The alteration of the trajectory is particularly troublesome in very hard materials, such as rock of igneous or metamorphic origin. Altering the direction of a borehole in rock has been accomplished by several techniques, which include: (a) the use of a wedge set within the borehole for the purpose of deflecting the drill string; (b) various stabilizers on a rotary drill string used in combination with high or low bit loads to achieve a change in the borehole trajectory; (c) a fluid jetting bit which can be used to preferentially erode one side of the borehole and thus deflect the boring tool in a direction of least resistance; (d) the use of a down-hole rotary motor incorporated into a bottom hole assembly in which the down-hole motor is used to rotate the drill bit. The bottom hole assembly contains a combination of bends and stabilizers to force the bit to cut preferentially in one direction. The bottom hole assembly applies a lateral force to the rotating drill bit which generally exhibits a side cutting capability as well as a forward cutting capability. Thus, by holding the alignment (tool face angle) of the bottom hole assembly constant, the bit cuts preferentially in one direction and the trajectory of the borehole changes. In some forms, the bottom hole assembly can be rotated, in which event the bit cuts a straight trajectory; and (e) the use of a bottom hole assembly which does not rotate and which includes pads that can be forced against the borehole wall in a controllable fashion. At the front of the assembly is a drill bit which can be rotated either by a down-hole motor or by an extension of a rotating drill string which passes through the bottom hole assembly. The pads on the bottom hole assembly can be actuated differentially to force the drill bit to cut with a lateral component and thus change the trajectory of the borehole.

WO 00/55468 PCT/AU00/00183 3 Most of the systems employed to change borehole trajectories are more suited for use in softer formations because they all use a rotating drill bit to cut rock. In harder rocks, a higher cutting rate is achieved by hammering a rock bit at the end of the borehole in a reciprocating manner. In deeper holes this is effectively accomplished by the use of a down hole hammer which is powered by drilling fluid. The fluid is commonly compressed air but may be water or some other fluid. Ideally, directional drilling in hard rock can be accomplished by the use of a similar cutting mechanism. In U.S. Patent Nos. 5,305,837 and 5,322,136, issued to Smith International, Inc., there is disclosed an air percussion drilling hammer for drilling through hard rock formations. In this type of drilling apparatus, the bit is reciprocated by an air driven piston and valve assembly that produces reciprocating impacts to the rock bit. The drilling apparatus also includes an internal mechanism which converts the reciprocating motion to rotary motion for rotating the rock bit as it is impacted against the rock portion of the borehole. This drilling apparatus can be utilized in directional drilling operations, in that the bit is rotated independent of the attached drill string. The disclosures of these two patents are incorporated herein by reference thereto.

WO 00/55468 PCT/AU00/00183 4 SUMMARY OF THE INVENTION The present invention utilizes standard fluid powered down-hole hammers to drill directional boreholes. In the system of the preferred embodiment, the down-hole hammer forms part of a bottom hole assembly. The direction of the down-hole hammer is disposed at an angle with respect to the axis of an up-hole section of the bore, and preferably tangential to the direction of the section of borehole being drilled. Thus, the hammer bit, which has little side cutting capability, drills in the direction in which it is pointed. This is achieved by the use of a combination of bends and stabilizers including offset stabilizers, which form part of the down-hole assembly. In the invention according to this embodiment, the direction is out of alignment with the previously drilled up-hole section as a consequence of the forward movement of the bottom hole assembly and in response to the bend and/or offset stabilizers. The direction of angular build is in the plane of the bend(s) of the bottom hole assembly and in the direction of the tool face angle. Alternatively, the angular build may be governed by the stabilizer offset alone. In directional drilling terms, the tool face angle is a projection of the direction in which the drill bit points on a plane perpendicular to the borehole, when viewed from the rear of the bottom hole assembly, toward the bit. The rate of angular build in terms of change of angle per unit length drilled is controlled by the geometry of the stabilizers and the bit, their relative positions, and the angular offset of the bottom hole assembly. For a hammer drill to operate, the bit must be rotated to a certain extent so that the buttons or chisels on the drill bit strike new areas of rock not previously struck during the bit's reciprocating motion. This is achieved in normal non-directional hammer drilling operations by rotating the drill string, and with it the down-hole hammer and drill bit. In the proposed directional drilling system, the bend in the bottom hole assembly imparts an angular build direction to the drill path when it is held at a constant tool face angle. To operate the device so as to effect a change in borehole trajectory, the tool face angle should be held constant. Therefore, a mechanism has been incorporated into the bottom hole assembly to achieve the rotation of the bit (and in this case the down-hole hammer), independent of the remaining bottom hole assembly.

WO 00/55468 PCT/AU00/00183 5 Hammer drills are designed to drill straight ahead and it is preferable to arrange the geometry of the bit, hammer, housing and stabilizers of the bottom hole assembly so that this remains the situation in the case of a directional down-hole hammer. In an embodiment of the invention, this is achieved by offsetting the projected center line of the down-hole hammer within the first stabilizer located behind the bit and down-hole hammer. The theoretical relation between angular build rate and the bottom hole assembly geometry can be represented mathematically. In an alternative embodiment of the invention, the intermediate bend can be removed so that the bit, down-hole hammer and housing are concentric about a common axis. For this assembly to drill a curved hole, the rear end of the bottom hole assembly is held eccentrically within the borehole by a stabilizer. Other stabilizers may be located between the bit and the rear stabilizer to maintain this offset position within the borehole. In this form, the hammer remains aligned tangentially to the curved hole at the location of the bit and therefore a curved borehole will be drilled. In this form it is preferable to place a bend behind the rear stabilizer in the direction of the tool face. This avoids a moment being developed that tends to force the bit to drill straight ahead. The bend may be exaggerated to force the bit toward the inside of the bend and thus tend to decrease the radius of the borehole being drilled. If a straight borehole section is to be drilled, then the entire bottom hole assembly can be rotated so that the tool face angle continuously changes during rotation. In this mode, the bottom hole assembly will drill a more or less straight but slightly oversize borehole. An angled hole using this assembly will tend to droop. If, however, the embodiment of the bottom hole assembly without the intermediate bend is rotated, it will tend to drill a straight hole which is not oversize. Less preferably, it is possible to furnish the bottom hole assembly with bend(s) in the direction of the tool face angle without the utilization of discrete stabilizers. Such an arrangement can be advantageous in the case of less stable ground so as to reduce the propensity of the bottom hole assembly to become trapped.

WO 00/55468 PCT/AU00/00183 6 The mechanism employed to rotate the down-hole hammer and bit involves attaching the down-hole hammer to the remainder of the bottom hole assembly by the use of a sub and bearing pack. A motor/gearbox assembly is incorporated into the bottom hole assembly and rotates the sub connected to the down-hole hammer and the bit. When a bend in the bottom hole assembly is utilized, the drive is accomplished through a flexible or articulated coupling. This need not be the case for the straight version according to another embodiment. Even though the drill string and bottom hole assembly are held at a fixed tool face angle, the down-hole hammer will be rotated by the motor and gearbox. The bottom hole assembly will thus be capable of drilling a hole with an angular build characteristic. The preferred form of the drive motor employed to rotate the hammer and bit is one which is powered by a pressurized fluid flowing in the drill string. This would in most cases be compressed air or gas, but can be other fluids. When compressed air is used to power the hammer, a vane motor can be utilized. When liquid is used, a positive displacement helical rotor progressing cavity fluid motor can be utilized. In either case, the drive motors could be advantageously coupled through a series of epicyclic gearboxes used as torque multipliers to the sub and the down-hole hammer. The coupling between the down-hole motor/gearbox combination and the hammer should be of the type that removes shock and withstands the torque generated when the hammer bit stops rotating. In the case of normal operations, the rotation of the bit will be momentarily interrupted each time the bit strikes the bottom of the borehole. In order to avoid excessive shock to the motor gearbox drive train, there is utilized an elastomeric coupling to absorb the rotational interruptions of the bit. In the event that the bit jams in the hole and the hammer is suddenly caused to stop rotating, an excessive torque may be developed in the motor/gearbox and coupling assembly due to the rotational inertia of the components contained therein. To avoid such adverse torque, it has been found to be advantageous to use a torque limiting clutch in the coupling assembly between the gearbox and the sub which rotates the hammer and bit. The rotational speed of the hammer and reciprocating bit with respect to the remainder of the bottom hole assembly should be controlled to optimize the penetration rate WO 00/55468 PCT/AU00/00183 7 for different types of rock formations. This is accomplished by means of a control module which contains some form of rotational speed governor that controls fluid flow through the motor. This may be pre-set or alternatively may be adjusted by means of electrical or fluid control signals conveyed from the collar of the borehole through a rod drill string to the control module containing such a governor. Alternatively, but less suitably, the fluid used to drive the rotational motor may be conveyed directly thereto by means of a tube disposed within the main drill string, such as the type used in reverse circulation drilling. In the event that the bit becomes jammed in the borehole it is essential to be able to apply torque to the bit so as to break it free. The motor/gearbox combination will not generally develop a sufficient amount of torque, and neither can it be developed if the rods are rotated. This is because the motor/gearbox combination will limit the available reactive torque. To permit an adequate amount of torque to be transferred to the bit from the drill string, the invention incorporates a unidirectional clutch mechanism which preferably takes the form of a ratchet and pawl mechanism. This enables the motor/gearbox assembly to rotate the hammer/bit combination freely. However, in the event the bit jams, torque can be transmitted through the drill string, bottom assembly housing to the sub, and therethrough to the hammer and the bit. To make full utilization of the directional drilling capabilities, the bottom hole assembly would normally contain a borehole survey tool to measure the azimuth, inclination and tool face angle of the bottom hole assembly. Geophysical probes can also be used in the survey tool module to enable detection of the types of rock being drilled. Communications between the borehole collar and the bottom hole assembly are desirable to make use of the information from the survey tool and from any geophysical probes contained in the bottom hole assembly. Also, communications to the bottom hole assembly permit adjustment of any governor incorporated in the motor speed control module. The simplest manner by which this information is transferred, and one which will work with compressed air as the drilling fluid, is by using electrical signals which pass through a series of insulated conductive rods contained within the drill string. These can be arranged so that the conductive rods become electrically continuous when the drill string sections are coupled WO 00/55468 PCT/AU00/00183 8 together. When, however, the drill string is pulled to the surface, the conductive rods can be disconnected as each tool joint is broken, but yet remain fixed within each section of the drill string. An alternative method used by the invention to transmit information along the rod string is by radio transmission which is preferably in the microwave range. When used in this manner, the drill rods function as waveguides.

WO 00/55468 PCT/AU00/00183 9 BRIEF DESCRIPTION OF THE DRAWINGS Further features and advantages will become apparent from the following and more particular description of the preferred and other embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters generally refer to the same parts or elements throughout the views, and in which: Fig. 1 shows a partial section of the bottom hole assembly; Fig. 2 illustrates an extension of Fig. 1, with the bottom hole assembly connected to a drill string and containing a conductive rod for electronic communications; Fig. 3 depicts an alternative form of the bottom hole assembly without a mid-housing bend, but with an offset rear stabilizer and a bend situated behind the stabilizer; Fig. 4 is a sectional view of the control module constructed according to the invention; and Fig. 5 illustrates the geometry of the bottom hole assembly together with the equations for calculating important parameters.

WO 00/55468 PCT/AU00/00183 10 DETAILED DESCRIPTION OF THE INVENTION Fig. 1 illustrates the elements of the bottom hole assembly according to one embodiment of the invention. For convenience and purposes of clarity, details of threaded or other conventional connections are not shown. In use, the bottom hole assembly would be connected to drill string sections that are coupled together in the traditional manner. A hammer drill bit 1 is driven in a reciprocatory manner by a down-hole hammer 2 which may be either driven by a liquid or gas medium. The fluid-driven hammer 2 typically produces 1,500-1,800 impacts per minute. Conventional air-driven hammers adapted for drilling operations are described in the paper titled Directional Air Hammer can Eliminate Expensive Location Costs, by Bui, et al., presented at the CADE/CAODC Spring Drilling Conference in Calgary, Canada on April 8-10, 1997, which paper refers to the Smith International Patents identified above, and the disclosures of which are all incorporated herein by reference. A sub 3 to which the hammer 2 is attached rotates within a bottom hole housing 4. The sub 3 is maintained in alignment in the housing 4 by a bearing pack comprising an axial thrust bearing 5, a radial bearing 6 and an axial bearing 7 retained by a nut 8. The housing 4 is tubular and is formed with a slight bend therein. The housing 4 can be bent at an angle in the range of about 0.1 -2.00 . The sub 3 is rotationally driven by a motor 14, via a gearbox 13, shaft 12, torque limiting clutch 11 and shock absorbing coupling 10 and flexible coupling 9. The motor 14 and gear reduction gear box 13 together provide sufficient torque for rotating the assembly to which it is connected, including the reciprocating hammer 2 and the rock bit 1. In the preferred embodiment, the motor output operates at about 10,000 rpm, and the gear reduction ratio is about 500:1. The output of this assembly is thus about 20 rpm. In other applications, it might be advantageous to use an air driven piston motor. The flexible coupling 9 may be of several forms including universal joint, constant velocity joint, elastomeric coupling or flexible shaft. The shock absorbing coupling 10 would preferably be an elastomeric device and may be combined with the flexible coupling 9. For powering itself, the motor 14 preferentially draws pressurized fluid from the annulus within the housing 4. This fluid may be drawn through and/or discharged through an optional control module 15. The motor drive fluid is either discharged via a port (not shown) WO 00/55468 PCT/AU00/00183 11 in the housing 4 into the borehole, or downstream of a flow restriction (not shown) in the housing 4. The fluid path is therefore down the drill string into the annulus, around an electronic survey package 16, control module 15, motor 14, gearbox 13, shaft 12, torque limiting clutch 11, shock absorbing coupling 10, flexible coupling 9 and through a port 17 in sub 3, into the down-hole hammer 2 and out through the bit 1 into the borehole. Some fluid passes into the control module 15 and then into the motor 14, or vice versa, and then back into the housing 4 or out of a port in the wall of the housing 4. The trajectory of the borehole is controlled by the position and diameter of the bit 1, a frontal thrust pad/stabilizer 18 and a rear stabilizer 19. The choice of separation between this apparatus and the angle of the bend in the housing 4 governs the rate of angular build of the bottom hole assembly. The frontal thrust pad/stabilizer 18 transfers the component of force that acts out of line with the drill string to the borehole wall. It should be noted that the center line of the bit 1 and down-hole hammer 2 projects to an eccentric position within the borehole at the location of the pad/stabilizer 18. The borehole survey module 16 is used to determine the position of the borehole geometrically and/or by geophysical measurements and calculations. A rod 21 in one drill string section permits electronic connections to other similar rods, and therethrough permits communications with the borehole collar. In another form, the rod functions as an antenna for radio communication up the drill string. This is preferably achieved in the microwave range using the drill string rod as a waveguide. A threaded tool joint 20 is located at the rear of the assembly. As is the usual practice, the stabilizers 18 and 19 are of conventional design and are made slightly under the gauge of the borehole to avoid jamming in the borehole. In the event that the bit 1 becomes jammed in the borehole, the drill string may be twisted up hole at the borehole collar, thus transferring a significant amount of torque to the directional assembly through the tool joint 20, to the bottom hole assembly housing 4 through the one-way clutch 22, to the sub 3 and WO 00/55468 PCT/AU00/00183 12 thence to the down-hole hammer 2 and bit 1. By permitting such a transfer of torque from the drill string to the bit 1, the tool may be recovered from a jammed situation. The one-way or unidirectional clutch 22 preferably takes the form of a ratchet and pawl assembly and is designed to permit free turning of the sub 3 under the normal rotational drive supplied by the motor and gearbox. Fig. 2 illustrates another embodiment of an extension of a section of a bottom hole assembly connected to a drill rod string 24 which contains communications rods 23 fixed in each section of the drill string. The communication rods 23 are connectorized to couple automatically on the assembly of the sections of the drill string and thus permit electronic communication between the bottom hole assembly and the up-hole borehole collar. The communication rods 23 are preferably insulated with ends held concentric within the drill string section, and fitted with an insulated connector that is sealed against fluid ingress. Fig. 3 is an alternative embodiment of a simplified bottom hole assembly. This bottom hole assembly omits the bend in the housing 4 and the forward pad/stabilizer 18 shown in Figs. 1 and 2, although the forward pad/stabilizer can be retained. As previously described, the bit 1 is connected to the down-hole hammer 2 which is in turn connected to the sub 3 and housing 4 which are held in an eccentric position within the borehole by a rear stabilizer 19. The housing 4 contains the rotational control and survey mechanisms as shown in Fig. 1. The drill string 24 is threadably connected to the housing 4. This connection 25 may optionally be flexible so as to transmit torque and thrust, but not to develop significant bending moments at the junction between the drill string 24 and the housing 4. Alternatively, the connection 25 may be manufactured in such a way that it includes a pre-formed bend to limit the lateral force developed on the outer side of the borehole, or indeed to force the bit towards the inner side of the borehole. The bend connection 25 may also be used in the form of assembly containing a bend and shown in Figs. 1 and 2. FIGURE 4 illustrates an embodiment of the control module 15. In this form, the control module 15 regulates the flow rate of fluid and thus the speed of the motor 14, the WO 00/55468 PCT/AU00/00183 13 pressure developed across the motor 14, and hence the torque that it can develop. In the drawing, pressurized fluid passes from the right to the left. The fluid, which normally may be compressed air, travels from the drill rods 23 through the tool joint 20 and through the drilled ports 30 to the left in FIGURE 4. The fluid is able to reach the chamber 28 adjacent to the piston 29 through port 27 formed in cap 26. The piston 29 is attached to a shaft 41 which forms a needle valve that is adjustably threaded into the piston 29. Some of the fluid is abstracted through ports in a filter 31 and therefrom into port 33 formed in adaptor 32. The adapter 32 is disposed between the regulator part of the control module 15 and the motor 14. The fluid then passes through an orifice 34 which restricts the flow rate of the fluid reaching the motor 14 and hence the peak speed of the motor 14. Return fluid from the motor 14 passes through a passage 35 into a chamber 36 in the adaptor 32 and then on through ports 37, 38 and 39. The return fluid then passes between the pointed tip of the shaft 41 and seat 40, and out of passage 42 into the borehole. A number of belville washers 43 force the piston 29 to the right. The pressure regulating function of the control module 15 is achieved by the movement of the piston 29 and with it the needle valve end of the shaft 41 from its seat 40. This controllable flow restrictor functions to regulate the outlet pressure of the motor 14 at a set pressure below the inlet pressure. The pressure is determined by the spring force developed across the belville washers 43 before the needle valve portion of the shaft 41 closes on the seat pressure P2 in chamber 44, plus the spring force exerted by the belville washers 43. If the pressure P2 in chamber 44 drops, as compared to the pressure P1 in chamber 28, then the piston 29 and shaft 41 move to the left, thereby closing the outlet between shaft 41 and seat 40. This action restores the pressure balance. The rear stabilizer 19 shown in FIGURE 4 is of the offset type in which the opening therein is not centered within the stabilizer 19. Rather, the top stabilizer portion shown in FIGURE 4 extends radially outwardly more than the bottom stabilizer portion. Thus, the drill string or other apparatus connected thereto is not centered in the borehole. The stabilizer 19 is otherwise of conventional design with axial surface grooves machined therein to allow for fluid to pass therethrough.

WO 00/55468 PCT/AU00/00183 14 Fig. 5 illustrates the geometry and equations of bottom hole assembly during operation thereof The bottom hole assembly is characterized by the bit 1, thrust pad/stabilizer 18, rear stabilizer 19, the distance L1 between 18 and 19, the distance L2 between the thrust pad/stabilizer 18 and the bit 1 and the acute angle <. This assembly is illustrated drilling a borehole with a radius R. The offsets of the center line of the assembly from the centre line of the borehole at the thrust pad/stabilizer 18 is r 0 o, and at the stabilizer 19 is r 03 . The offset of the center line of the leg L 1 from the center line of the borehole is r 02 . The equations presented in the drawing describe the geometrical relationships. In the event that the assembly is straight without thrust pad/stabilizer 18 as described in Fig. 3, then the equations simplify but the form shown remains correct. While the preferred and other embodiments of the method and apparatus have been disclosed with reference to specific bottom hole assembly, it is to be understood many changes in detail may be made as a matter of engineering choices without departing from the scope of the invention as defined by the appended claims. Indeed, those skilled in the art may prefer to embody the apparatus in other forms, and in light of the present description they will find it easy to implement that choice. Also, it is not necessary to adopt all of the various advantageous features of the present disclosure into a single composite bottom hole assembly in order to realize the individual advantages.

Claims (24)

1. A bottom hole drill assembly, comprising: a bit adapted for drilling a borehole in rock; a motor in said bottom hole drill assembly, said motor coupling to said hammer a rotary motion for rotating said hammer to thereby rotate said bit.

2. The bottom hole drill assembly of Claim 1, further including a housing with a bend, and one or more stabilizers to enable drilling of a curvilinear hole without rotating a drill string attached to said assembly.

3. The bottom hole drill assembly of Claim 1 or 2, further including a frontal thrust pad/stabilizer and a rear stabilizer to force the assembly to drill a curved trajectory without drill string rotation.

4. The bottom hole drill assembly of Claim 1 or 2, further including an offset rear stabilizer to force the assembly to drill a curved borehole without drill string rotation.

5. The bottom hole drill assembly of Claim 1, further including a bend to force the assembly to drill a curved borehole.

6. The bottom hole drill assembly of Claim 1, 2, 3, 4 or 5, further including a bend located behind a rear of said assembly in a plane of and assisting the drilling of a curved borehole.

7. The bottom hole drill assembly of Claim 1, 2, 3, 4 or 5, further including a flexible coupling for transmitting torque to said hammer.

8. The bottom hole drill assembly of Claim 1, wherein said motor is driven by a fluid that is used to drive said hammer.

9. The bottom hole drill assembly of Claim 1, wherein said motor is driven by a supply of fluid independent from that used to drive said hammer. WO 00/55468 PCT/AU00/00183 16

10. The bottom hole drill assembly of Claim 1, further including a gearbox coupled to said motor for providing torque multiplication.

11. The bottom hole drill assembly of Claim 1, further including an elastic shock absorbing flexible coupling for protecting said motor from rotational shock associated with an impact of the bit.

12. The bottom hole drill assembly of Claim 1, further including a torque limiting clutch for protecting said motor from rotational shock of said bit jamming in the borehole.

13. The bottom hole drill assembly of Claim 1, further including a unidirectional clutch located between a housing connected to a drill string and a sub connected to said hammer such that under normal motor operation in rotating said hammer said clutch freewheels, and when said drill string is turned the torque is transmitted to the down-hole hammer and bit via said unidirectional clutch.

14. The bottom hole drill assembly of Claim 1, further including a motor speed control controlled from a borehole collar.

15. The bottom hole drill assembly of Claim 1, further including directional guidance sensors providing geometric or geophysical measurements.

16. The bottom hole drill assembly of Claim 1, further including a respective communication rod fixed within each section of drill pipe and adapted for automatic connection when the drill string sections are secured together.

17. The bottom hole drill assembly of Claim 16, whereby information is transmitted electronically to or from a borehole collar by means of radio communication through the drill string.

18. The bottom hole drill assembly of Claims 17, whereby a frequency of the transmission is in the microwave range so tuned that the drill string functions as a waveguide. WO 00/55468 PCT/AU00/00183 17

19. A method of drilling percussion comprising the steps of: using a down-hole hammer and bit to erode a rock formation; rotating said down-hole hammer and bit by a down-hole motor/gearbox assembly so that it is not necessary to rotate a drill string to rotate the drill bit.

20. The method of drilling percussion of Claim 19, further including the step of incorporating a series of bends and/or stabilizers in a bottom hole assembly for drilling a curvilinear path while not rotating the bottom hole assembly.

21. The method of drilling percussion of Claim 20, further including the step of rotating the bottom hole assembly with the drill string to bore a straight hole.

22. The method of drilling percussion of Claim 19, further including the step of communicating between a borehole collar and a bottom hole assembly by means of electrically connected rods fixed within the drill string.

23. The method of drilling percussion of Claim 19, further including the step of communicating information between a borehole collar and a bottom hole assembly by means of radio communication within the drill string.

24. The method of drilling percussion of Claim 23, further including the step of communicating radio transmissions in a microwave range so that the drill pipe functions as a waveguide.