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Title:
EXTENDED REACH DRILLING
Document Type and Number:
WIPO Patent Application WO/2013/095164
Kind Code:
A1
Abstract:
Apparatus, methods and uses that allow extended reach drilling by virtue of the provision in the drillstring and to downhole tools collective vibrations, not tuned specifically to a single resonant frequency, from a hammer assembly that provides vibrations of different frequency ranges.

Inventors:
WEST GREGORY DONALD (NZ)
CUNLIFFE MARK CHRISTOPHER (NZ)
Application Number:
NZ2012/000240
Publication Date:
June 27, 2013
Filing Date:
December 18, 2012
Export Citation:
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Assignee:
FLEXIDRILL LIMITED (220 Lake Road, Takapuna, Auckland 0627, NZ)
International Classes:
E21B1/00; E21B4/06; E21B6/00; E21B6/04
Domestic Patent References:
WO2004073932A1
Foreign References:
US20100319994A1
EP1239112A2
US20060225922A1
US20100108384A1
Other References:
See also references of EP 2795032A4
Attorney, Agent or Firm:
DEVINE, Matthew, D et al. (A J Park, PO Box 949, Wellington 6140, NZ)
Download PDF:
Claims:
Claims

1. A method of extended reach drilling which comprises

providing a top hammer assembly from which a drill string is dependant, the top hammer assembly, or the top hammer assembly and the proximate region of the drill string, being configured by mass or cross sectional impedances, excitation features, or the like to provide excitations to provide multiple localised bands of frequencies that differ from the band or bands of frequencies (beat frequency) generated at the strike interface, the variation of frequencies sufficient to allow extended reach drilling, and operating the top hammer assembly during operation of the drill string in an extended reach drilling operation, without specifically tuning the drill string for resonance , although some optimisation responsive to different strata might occur.

2. A method as claimed in claim 1 wherein said top hammer to be powered by hydraulic, pneumatic, electric, mechanical or electromagnetic means.

3. A method of extended reach drilling which comprises

providing a top hammer assembly from which a drill string is dependant, the top hammer assembly, or the top hammer assembly and the proximate region of the drill string, being configured by impedances, excitation features, masses, or the like to increase the spread of vibrational frequencies to pass into and downhole along the drill string from those generated at the impact interface of the top hammer assembly,

the method comprising operating the top hammer assembly during drill string dependant downhole operations at a power, or in a finite power range, into the top hammer assembly, without reference to drill string length for resonance purposes.

4. A method of claims 1 to 3 wherein there are subsequent uphole frequencies reflected from those generated at the strike or impact interface of the top hammer assembly.

5. A method of enhancing the reach of a drill string downhole using a top hole hammer functionality, the method comprising, without tuning for resonance, generating a spectrum where the output energy of the hammering impacts at least to some extent is localised to first order of magnitude spread of frequencies, yet the configuration uphole of the drill string supporting assembly is such that, by impedance, excitation, mass affects, or the like, a greater spectral spread of the vibrational energy, and of frequencies over several orders of magnitude, passes downhole thereby to enable the extended reach drill string operations, and

operating the drill string with such a modified spectrum of vibrational frequencies passing into it.

6. A drilling apparatus having a top hole hammering functionality able, , to support and/or provide vibration to a drill string that extends downhole and to allow deep reach drilling activities characterised in that a spectrum of different orders of magnitude of vibrational frequency are or can be passed into the drill string without reference to its length, from an impact generated spectrum of lesser order of magnitude of vibrational frequency spread not, of itself, able to allow the deep reach drilling activities.

7. A top hammer apparatus for usage in extended reach drilling operations characterised in that an impact produced range of vibrations in the range of from 0 to 100 Hz not sufficiently of an energy to allow extended reach drilling operations is modified by passive configurational features of the assembly to allow and/or produce bands of vibrations in each of the ranges 0 to 100Hz, 100Hz to 1000Hz and 1000Hz to 10000Hz.

8. Apparatus of claim 7 wherein the i length of the stress waves are very short. for example the wave length = the speed of sound in steel (5,000 metres per second) divided by the frequency, so the wave length at 10,000 Hz = 0.5 Meters, at 1,000 Hz = 5 meters, at 100 Hz = 50 Meters

9. Apparatus including a drill string and drill string dependent tool where there is provision from within and/or without the drill string to generate for and/or to the drill string, for and/or to the tool, or both, a frequency or a range of frequencies to provide multiple vibration(s).

10. Apparatus as claimed in any of claims 5 to 8 wherein said apparatus includes a top hammer that is configured with impedances, excitation features, masses or the like to provide said frequencies.

11. Apparatus of claim 9 wherein the range or frequency can be defined as going from a first to a Nth range.

12. The use of a first frequency or frequency range and at least a second frequency or second frequency range in a drill string having a drill bit.

13. The use of claim 12 wherein any number (N) of frequencies or frequency ranges are used.

14. The use of claim 12 or 13 wherein some or several frequencies are non-incident. 15. An oscillating (vibrational) apparatus that outputs at least two vibrational frequencies and/or frequency ranges with first frequency or frequencies in the kilohertz range e.g. (> 1000 Hz) and the second frequency or frequencies in the tens hertz range e.g. (< 100 Hz) for drilling through sub terrain.

16. Apparatus of claim 15 wherein frequencies within the following ranges 0-100 Hz, 100 -1000 Hz, 1000 -10,000 Hz, etc are generated by both incident frequencies of a strike and nonincident and/or impeded frequencies resulting from the strike.

17. A multi-oscillating (vibrational) apparatus capable of being tailored to drill through sub terrain reliant on specified or discrete frequency or frequency ranges for specific purposes in the drilling function.

18. An impact/vibrational assembly capable of impacting a drill bit on a bore face, the assembly comprising or including

a drill string,

a drill bit, and

a drill head, that is capable of attaching to the drill string,

wherein each of the drill string, drill bit and drill head each have a mass, or masses, that can be excited to vibrate at functional frequencies.

19. An assembly of claim 18 wherein the drill head provides with a striking directly some functional frequencies and said masses responsive to the striking provides other functional frequencies to which at least one of the drill string and drill bit responds with an excitation.

Description:
EXTENDED REACH DRILLING

The present invention relates to extended reach drilling.

The invention more particularly, but not solely, relates to methods of extended reach drilling, with a drilling apparatus able to effect extended reach drilling and operation of a downhole drill string in extended reach drilling with the generation and transfer of enabling or synergistic spread of vibration. Methods of enhancing the reach of a drill string and downhole tooling using a top hammer, the method comprising, without specifically tuning for resonance, generating a spectrum where the output energy of the hammering impacts at least to some extent is localised to first order of magnitude spread of frequencies, yet the configuration uphole of the drill string supporting assembly (the impacting or vibrational device) is such that, by impedance, excitation, mass affects, or the like, a greater spectral spread of the vibrational energy, and of frequencies over several orders of magnitude, passes downhole and/or in combination with some subsequent frequencies being reflected back uphole thereby to enable the extended reach drill string operations, and operating the drill string with such a modified spectrum of vibrational frequencies passing into it.

Top hammer drilling has been used for many years within the mining industry to rapidly advance drill bits into ground formations.

These top hammers have traditionally been energised by either pneumatic or hydraulic power. Such hammers are designed to generate large impact shock waves with minimal mechanical impedance between the impacting piston and the drive shaft (the connection between the piston and the drill rods) via drill rods to a drill bit and providing large amplitude of movement, giving very rapid penetration through relatively short distances, as has been the requirement for blast holes - typically up to 30 meters.

While this is an effective energy delivery mechanism, it does not excite other non-impact frequencies that give rise to other functions that aid in extended reach drilling, such as fluidisation of the formation. In addition, these types of hammers require the use of coarse "rope" type threads on the drill rods, which in use, see a significant energy loss across the thread of approximately 6% per drill thread, limiting the practical distance that these types of drills can operate at to approximately <50 meters.

"Sonic" drill rigs, (which aim to "tune" the vibration input to a specific resonant mode, and generally achieve the resonance by rotating eccentric masses), are also depth limited (owing to the substantial horsepower requirements and the practicalities of mechanical devices operating at extremely high revolutions per minute (RPM's) which are required with these devices when trying to drill at second, third, or fourth resonant modes) to generally around 100 meters. Such difficulties can be avoided by the approach we propose be used, Another advantage as well will be the very modest input power requirements.

Either of the aforementioned is an, or another, object of the invention.

The spread of vibrational frequencies proposed with the present invention, has proven able to drill all formations, even when large diameter drill bits/reamers (for example up to 250mm in diameter) are used. Moreover such - multiple mode resonant and/or non resonant) drilling can achieve a distance of potentially hundreds of meters, albeit at a slower rate and without excessively large impact force, or large axial displacement in the drill string or at the drill bit.

The present invention envisages using impact pulses and wide spread bands of vibrations to advantage when drilling. The invention also relates to the use downhole of a first frequency, or a first frequency range (e.g. able to break rock with or without resonance) and a distinct second frequency, or second frequency range (e.g. to avoid formational grab on the drill string), to excite, for different functionalities, the drill string and/or the tool or bit.

Any number (N) of frequencies or frequency ranges can also be used to advantage.

Whilst the advantages of choosing a resonant mode has been recognised as advantageous when drilling with sinusoidal excitation devices (rapidly rotating eccentric drives commonly used in so called Sonic drill rigs) in underground formations, many drilling applications occurs without reliance on solely exciting a single resonance of the drill string.

We believe there is a considerable benefit to be derived in including, by any suitable means, and most preferably passive features or configurational features of a top hammer assembly, means whereby vibrations of different frequency ranges can provide a synergistic outcome where the resulting collective vibrations are not tuned specifically to a single resonant frequency.

It is another object of the present invention, to derive for the drill string and its tool or bit deliberate performance enhancing mixed frequencies from a top hammer functionality.

In an aspect the invention is a method of extended reach drilling which comprises

providing a top hammer assembly from which a drill string is dependant, the top hammer assembly, or the top hammer assembly and the proximate region of the drill string, being configured by impedances, excitation features, or the like to provide excitations to provide multiple localised bands of frequencies that differ from the band or bands of frequencies to be generated at the strike interface, such band(s) at the strike interface themselves(s) not of a power (due to the mechanical impedances designed into the system) or variation of frequencies sufficient to allow extended reach drilling, and operating the top hammer assembly during operation of the drill string in an extended reach drilling operation, without reference to drill string length variation, although some optimisation responsive to the manipulation of the impacting frequencies in different strata might occur.

In an aspect the invention is a method of extended reach drilling which comprises

providing a top hammer assembly from which a drill string is dependant, the top hammer assembly, or the top hammer assembly and the proximate region of the drill string, being configured by impedances, excitation features, masses, or the like to increase the spread of vibrational frequencies to pass into and downhole along the drill string from those generated at the impact interface of the top hammer assembly,

the method comprising operating the top hammer assembly during drill string dependant downhole operations at a power, or in a finite power range, into the top hammer assembly, without reference to drill string length for resonance purposes.

In another aspect the invention is a method of enhancing the reach of a drill string downhole using a top hole hammer functionality, the method comprising, without tuning for resonance,

generating a spectrum where the output energy of the hammering impacts at least to some extent is localised to first order of magnitude spread of frequencies, yet the configuration uphole of the drill string supporting assembly is such that, by impedance, excitation, mass effects, or the like, a greater spectral spread of the vibrational energy, and of frequencies over several orders of magnitude, passes downhole thereby to enable the extended reach drill string operations, and

operating the drill string with such a modified spectrum of vibrational frequencies passing into it.

In another aspect the invention is a drilling apparatus having a top hammer functionality able, top hole, to support and/or provide vibration to a drill string that extends downhole and to allow deep reach drilling activities characterised in that a spectrum of different orders of magnitude of vibrational frequency are or can be passed into the drill string without reference to its length, from an impact generated spectrum of lesser order of magnitude of vibrational frequency spread not, of itself, able to allow the deep reach drilling activities.

In another aspect the invention is a top hammer assembly usage in extended reach drilling operations characterised in that an impact produced range of vibrations in the range of from 0 to 100 Hz not sufficiently of an energy to allow extended reach drilling operations is modified by passive configurational features of the assembly to allow and/or produce bands of vibrations in each of the ranges 0 to 100Hz, 100Hz to 1000Hz and 1000Hz to 10000Hz. It is this frequency rich vibrational content that cause the down hole tools (drill rods, drill bits, reamers etc) to become excited and vibrate at multiple frequencies- but with (compared to conventional top hammers) small displacement amplitudes that minimise frictional damping in the drill string and therefore allows for efficient energy transfer to the drill bit which collectively and synergistically allow extended reach drilling operations.

Preferably the impulse length of the stress waves are very short and

synergistically allow extended reach drilling operations.

In another aspect the invention is apparatus including a drill string and drill string dependent tool where there is provision from within and/or without the drill string to generate for and/or to the drill string, for and/or to the tool, or both, a frequency or a range of frequencies to provide multiple vibration(s).

The range or frequency could be defined as going from a first to a Nth range. In another aspect the invention is the use of a first frequency or frequency range and at least a second frequency or second frequency range in a drill string having a drill bit.

Optionally any number (N) of frequencies or frequency ranges can be used.

Whilst all frequencies can be generated (e.g. by an oscillator) to be incident downhole some or several frequencies can be non-incident (e.g. reflected).

And such reflected and/or incident frequencies may be caused to vary by the nature of the overall apparatus.

In another aspect the invention is an oscillating (vibrational)apparatus that outputs at least two vibrational frequencies and/or frequency ranges with first frequency or frequencies in the kilohertz range e.g. (>1000 Hz) and the second frequency or frequencies in the tens hertz range e.g. (<100 Hz) for drilling through sub terrain.

Envisaged are frequencies within the following ranges 0-100 Hz, 100 -1000 Hz, 1000 -10,000 Hz, etc.

In another aspect the invention is a multi-oscillating (vibrational) apparatus capable of being tailored to drill through sub terrain reliant on specified or discrete frequency or frequency ranges for specific purposes in the drilling function.

In another aspect the invention is an impact/vibrational assembly capable of impacting a drill bit on a bore face, the assembly comprising or including

a drill string,

a drill bit, and

a drill head, that is capable of attaching to the drill string,

wherein each of the drill string, drill bit and drill head each have a mass, or masses, that can be excited to vibrate at functional frequencies. Preferably the drill head provides with a striking directly some functional frequencies and said masses responsive to the striking provides other functional frequencies to which at least one of the drill string and drill bit responds with an excitation.

Optionally the excitation is by means of one or more oscillator(s) whether in the drill string, in the drill head, in the drill bit, or some hybrid of those choices.

The device may optionally or preferably have dampers that negate non useful frequencies.

Preferably the primary vibrational frequencies are totally or in part generated by, hydraulic, pneumatic, eccentric drive, electromagnetic, electric, or mechanical top hammer functionality.

As used herein "extended reach" contemplates drilling to greater, and indeed very much greater than, say, 50 metres.

It is envisaged that the capabilities are to allow downhole operations (drilling, reaming, etc) that extend for deeper than the depths of 30 metres, 50 metres and 100 metres acknowledged as depth limits for existing techniques.

As used herein the term "(s)" following a noun means one or both of the singular or plural forms.

As used herein the term "and/or" means "and" or "or". In some circumstances it can mean both.

This invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more of said parts, elements or features, and where specific integers are mentioned herein which have known

equivalents in the art to which this invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.

A preferred form of the present invention will now be described with reference to the accompany drawings in which

Figure 1 shows a conventional hydraulic/pneumatic top hammer arrangement, the impact device being on the right and involving a hammering shuttle (commensurate to its impact face in cross-section) responsive to input pressure(s) and exhaust actuation (shown diagrammatically) and subject to drill string rotation apparatus to drive a downhole drill bit or other downhole tool, these top hammers generating significant impact force of (relatively) long duration which provides significant force and large amplitudes of movement of the drill bit into the formation - but with most of the impact energy in frequencies at or near the beat frequency (the number of hammer impacts per second) but without generating significant additional frequency rich vibrational content of very short duration Figure 2 shows a typical impact graph resulting at the interface from the hammering effect of an arrangement as in Figure 1,

Figure 3 shows a sonic drill arrangement, this time reliant on eccentrics to generate substantially sinusoidal inputs, but again showing a drill string rotational apparatus and a downhole drill bit,

Figure 4 shows a typical sinusoidal output of such an eccentric driven vibrational arrangement for sonic drilling,

Figure 5 is the conceptual arrangement of the present invention showing an impact device to the right acting down a drill string to a drill bit or other downhole tool (optionally via a spring), the impact device being hereinafter described in more detail by reference to an example,

Figure 6 shows an extended reach hydraulic or pneumatic top hammer arrangement as an example in accordance with the present invention to be the impact device at the right of, for example, the layout as in Figure 5 or to operate without the spring arrangement shown,

Figure 7 shows a still further embodiment reliant on a hydraulic or pneumatic top hammer arrangement,

Figures 5,6,&7 showing embodiments of an extended reach Top hammer device, whereby the various masses, dimensional changes and stiffnesses of the assembly encourage a broad band pulse of vibrational energy to be transmitted to the dill string when excited by a short duration impact (~ 0.0005 s ) of relatively low energy

(compared with a conventional Top hammer) whereby the high frequency vibrations are believed to reduce frictional losses in the drill string and the drill bit (or other tools) vibrate at a multitude of frequencies and low - mid frequency vibrations excite drill rod vibrational modes with very small amplitude of movement (compared to a conventional Top hammer, and

Figure 8 shows a typical spectral plotplot (Amplitude/Frequency) of the response downhole resulting from an impact when using an extended top reach hammer such as shown in Figure 5, 6, or 7

Within the drilling and construction industries, there is an ongoing need to drill / ream or otherwise manipulate the ground formation at higher speeds or with greater efficiency. Various devices such as top hammers and down the hole hammers have been used to good effect in these challenging environments, however our testing has shown that in addition to using an impact device with various masses and impedences which generate frequency rich vibrations, this when used in association with specifically designed ground engaging tools (drill rods, reamers, compactors, drill bits etc) which are receptive to at least one vibrational frequency (delivered via the drill rods), can give substantial performance improvements. This concept is the basis for this invention. The concept of downhole excitation is not new and several methods have been used such as;

Hammer devices - these produce impulses to the ground engaging tool - (but the tool is not designed to become excited by these impulses) in a random manner but the ground engaging device (drill bit / reamer etc) is not designed to become

independently excited

Resonance devices - (such as eccentric drive "sonic" devices) strive to resonate the entire drill string - thus causing an axial (hammering) movement back and forth of the drill bit.

As can be seen in Figure 1 conventional hydraulic or pneumatic top hammers strive to have a very similar cross section between the piston and the impact face. This is required for optimum energy transfer and amplitude of movement from the hammer to the drill rods and ultimately the drill bit. (impedance matching).

Shown is an impact device 1 with a reciprocatable piston, anvil or shuttle 2 as the hammer to strike at least one impact face 3 forming part of or connecting

vibrationally to the drill string of drill rods 4 down to the downhole tool 5. A rotational drive apparatus 6 to rotate the drill string of rods 4 is provided.

To be noted is the close cross-sectional relationship of the member 2 to the drill string of rods.

This design results in a very clean impact wave at (substantially) the frequency of the strike of the piston( beat frequency) with minimal loss of energy through the system and maximum force and displacement at the rock face. See Figure 2.

This arrangement drills hard rock very rapidly - although the distance (or depth) capability is typically less than 50 meters.

The eccentric vibrational apparatus 8 of Figure 3 generates likewise into a drill string of rods 7 to a drill bit 9, the drill string being rotatable by a drive 10.

The sonic drill system of Figure 3 generates a smooth sinusoidal force wave (as in Figure 4) from the input of the rapidly rotating eccentric masses.

For this system to be effective the drill rods themselves are excited to resonance - thereby giving amplitude to the drill bit. While this system is very effective in overburden and non cohesive ground conditions the input speed of the eccentric drives needs to be constantly adjusted to enable the ever changing drill string length to be kept in resonance.

Apart from drivability issues the depth to which sonic drill rigs can operate is ultimately dictated by the speed to which the eccentrics can be rotated. It is also important to note that there is a one to one relationship between the input frequency and the drill rod/bit frequency (e.g. if 100Hz is required to maintain resonance in the drill string - then an input frequency of 100Hz is required). Our device is quite different to these systems in that what we propose allows the drill bit to become excited and therefore oscillate INDEPENDENTLY and at higher frequencies than the drill string.

We are aware of a system that endeavours to achieve similar results - this being the Wiercigroch patent # US 2010/0319994 Al. This device is a very complex apparatus that uses piezoelectric transducers, in conjunction with complex algorithms and computer control, to try and resonate a drill bit at a similar frequency to the resonant frequency of the formation being drilled. There has also been work done by Uitto Et al - #4671366 whereby they measure the stress wave and actively modify the spectrum of the stress wave.

Keskiniva WO 2010/037905 Al has a feed back device for controlling reflected stress waves.

Keskiniva US 7891437B2 looks to optimise impact force and the length of the stress wave.

Watanabe US 6454021 Bl uses a magnetostrictive material with an electrical pulse and coil to alter the pulse characteristics of the drilling machine.

None of the above art deliberately induces multiple frequencies (in fact quite the converse) to enhance extended reach drilling operations. Our device by contrast is not a feed back driven device - nor is it like a hammer drill, rod and bit or a sonic drill rod and bit. Rather by having an understanding of the frequency(s) generated by either a hammering device or resonant device - testing has shown that it is possible to design the ground engaging tool as a separate spring / mass system that itself becomes excited - independently of any excitation or vibration happening within the drill string - giving impressive productivity gains. See the discussion below about Figure 8.

Figure 5 shows a system with an impact device 11 such as will be described with respect to the present invention driving directly or indirectly down a drill string of rods 12 to a drill bit or other downhole tool 13. A spring 14 can be provided in the drill string.

Figure 6 shows a preferred embodiment. An impact device 15 interacts with a drill string 16 to a drill bit 17 or other downhole tool. The drill string 16 is one with drill rods 18 and a drive to rotate the drill string. This drive 19 can be positioned

appropriately. Shown as part of the impact device 15 are primary and secondary masses 20 and 21 respectively. Masses 20 and 21 are movable relative to the surrounding structure 22 (e.g. by moving one or the other of the shuttling anvil or its surround, or both). As can be seen, at least for the mass 20, there is shown a pair of opposed impact faces A and B to act alternately and respectively with impact faces A and B of the surround structure 22.

With the input pressure (preferably being hydraulic or pneumatic) and exhausting being provided, appropriate reciprocating or shuttling of a known kind can be created.

It can be seen however that, transverse to the reciprocation axis, the cross- sectional extent of the masses 20 and 22 is quite significantly different from that of the drill string 16 and thus will act as impedances.

The discussion below in respect to the response / spectrum plot of Figure 8 is achievable with an embodiment typified by Figure 6.

The quite different embodiment of Figure 7 shows another alternative way (again with input pressures and exhaust pressures) able to cause, as a piston, the member 23, as an anvil, to move backwards and forwards in alignment with the drill string direction so as to impact on impact face 24 and impact face 25. In this arrangement an isolation spring 26 can be provided and there can be input to turn the drill bit from zone 27.

It is to be noted also that there is the option of adding an impedance in the way of a change in cross-sectional area of the drill string by addition of a mass 28 which acts on the member 29 connected via drill rods 30 to the drill bit 31.

A similar output to that disclosed in the spectral plot of Figure 8 is achievable. With regards to the extended reach hydraulic or pneumatic top hammer, of which Figure 6 is an example, it is clear that the design is significantly different from both the conventional top hammers or sonic drive systems.

We have found by contrast to the conventional system of Figure 1, that by designing this system with significant changes in mass and stiffnesses we get a significant reduction of force through the hammer - (e.g. if the input strike force is 40 ton - the resulting force being passed from the hammer to the drill rods may be only approx. 15 ton).

However while the peak force is diminished through this design - the initial impact frequency is broken into multiple frequencies of varying magnitude as the impact wave travels longitudinally through the hammer and causes the primary and secondary masses (there may be more than two) connected by various stiffnesses to vibrate over a wide band of distinct frequencies. These distinct stress wave vibrations move down the drill string to the drill bit. It is speculated that the larger amplitude vibrations carry out the majority of the rock breaking - while the higher frequency vibrations also assist in localised rock fracture - but more importantly cause fluidization of the formation being drilled and minimise "frictional grab" (damping)on the drill rods.

The multiple frequencies generated by this arrangement can clearly be seen in the response spectrum plot of Figure 8 -with distinct frequencies in the lO's of Hz - 100's of Hz and 1,000 Hz. Each of these multiple frequencies are the result of a single input strike - in reality the impact the impact (strike) rate of this hammer is from 50Hz to many hundreds of Hz. These high frequency impacts are readily achievable if the hammer is set up to impact in both directions (on both the A-A faces and the B-B impact faces).

In practice this arrangement has allowed us to drill in excess of 150 meters - allowing for true extended reach top hammer drilling operations.

In our testing we have found that an appropriately designed reaming tool and "supplied" with an impact frequency input of 50Hz is capable of itself vibrating in excess of 1,000 Hz. In fact, if the desired excitation of the ground engaging device, is 1,000 Hz, then the input vibration (from any suitable source) can be at any sub harmonic frequency such as 500 Hz, or 250 Hz, or 125Hz etc.

As example of the present invention, with reference to Figure 6 or 7, a hammer that provides an initial impact or hitting force of 40 tonnes will provide an output force at the drill bit of between 12-15 tonnes. Such a hammer will be operated at 50Hz. The reduction in peak force, being between 25-27 tonnes, is into the creation of the multiple frequencies as shown in the spectral plot of Figure 8 or some other version with multiple localised bands of frequencies, each with its own amplitude spread.

The data ( spectral plot) of Figure 8 shows how a reamer can be excited to over

1,000 Hz. The input frequency from the top hammer while only generating 50Hz resulted in dramatically faster penetration rates owing to the response.

Figure 6 and 7 suggest how a hydraulic or pneumatic top hammer can achieve outcomes wanted. The piston or hammer is propelled into the drive shaft by (probably) hydraulic or pneumatic energy, or mechanical energy (e.g. rotating eccentric masses). By adding/changing the position and/or number of masses of various stiffness's and by altering the mass/stiffness of the piston the spectral spread varies.

Ideally the top hammer assembly usage in the extended reach drilling operations is characterised in that an impact produced range of vibrations in the range of from 0 to 100Hz, not sufficiently of an energy to allow extended reach drilling operations, is modified, by passive configurational features of the assembly, to allow and/or produce bands of vibrations in each of the ranges 0 to 100Hz, 100Hz to 1000Hz and 1000Hz to 10000 Hz which collectively and synergistically allow extended reach drilling operations. We believe there is an advantage in generating a profile of multiple spectrum vibrational frequencies that, when combined, together, provide numerous advantages over conventional technologies including the following:

Ability to drill a hole with a greater diameter than conventional methods allow.

Allowing easy penetration through loose overburden formations (clay, sand, gravel etc) while at the same time having enough penetration power to drill through hard competent rock formations.

Ability to drill and recover quality core samples through various formations (rock/clay etc) - whereby most conventional systems have either not enough penetrative power to drill competent rock - or so much impact energy that the desired rock sample is reduced to dust.

Ability to drill deeper through a minimisation of friction on the drill string which allows for extended reach operations (e.g. oil tube drilling, or in long horizontal sections) which conventional mechanisms are not able to achieve.

Can be used as a double acting hammer to generate higher impact frequencies

Not necessary to tune the oscillating force and or the drill string to

vibrate/oscillate in a single resonant mode as with "sonic" drilling.

Preferably the apparatus is able to deliver two (or more) identifiable frequency bands via the drill string to the formation that is being drilled. Such frequencies can be generated by a top hammer apparatus that is made up of different components - wherein each component has differing masses each connected by varying stiffness elements and varying ratio dampers that results in the apparatus having several differing natural frequencies. Each natural frequency can be determined by the usual formulae for such systems with appropriate changes made to the masses and stiffness of the material of each component to alter the natural frequencies generated.

While this system may not be as effective in drilling rapid small diameter holes in hard rock over short distances (as with conventional percussive drills) - the various frequencies and impedances mean that using more aggressive threaded drill rod connectors that are not "rope" style is practical - these different threads are not prone to cyclic loosening and tightening.

The present invention is to generate multi frequencies that allows drilling in various formations to long distances - potentially hundreds of meters.

The specific vibrations work to minimise friction on the drill string, and are sufficient to allow competent rock formations to be penetrated.

In practice the frequencies could provide at least one frequency in the kilohertz range (above one thousand Hz) and another frequency operating in the tens of Hz range (e.g. 60 Hz). Such frequencies are dependent on the masses of each individual part making up the drilling assembly, where each part has its own inherent natural frequencies such that the combination of frequencies generated can enhance, cancel out, or maintain the multitude of frequencies generated.