The present invention relates to drilling devices in which fluid column resonance is used to generate an impulse force.
Conventional rotary drilling devices comprise a rotary drill bit, such as a tricone rotary drill bit, arranged at the end of a drill string which is rotated by a machine to cause the drill bit to penetrate the rock to be drilled. The penetration rate, and thus the drilling speed, is dependent on the rotation rate of the drill string and the Weight on Bit applied to the drill bit.
Percussion assisted rotary drilling arrangements have been proposed, such as that disclosed in U.S. Patent Application Publication No. US 2013/0098684. In this arrangement, rotary drilling is assisted by pneumatic down-the-hole drilling in order to improve drilling speed. However, the output power of the hammer must be limited to very low values in order to prolong the life of the tricone rotary drill bit, as the high impact forces generated by the down-the-hole hammer causes significant wear on the bit.
Another arrangement is disclosed in International Patent Application No. WO 2007/042618, which includes both a percussion device and a rotation motor with a tricone rotary drill bit, wherein the rotation motor rotates a drill rod and the drill bit and the percussion device provides stress pulses of low amplitude at high frequency via a drill rod and the drill bit. However, the impulse device required to generate the high frequency stress pulses is complex.
It is desirable to provide a drilling device that overcomes a number of the disadvantages associated with existing devices. In particular, it is desirable to provide a drilling device that produces a drilling action that can be used alone, or to enhance the drilling speed of rotary drilling.
The present invention relates to a drilling device comprising:
at least one drill rod, the or each drill rod having a first cylindrical wall defining an elongate chamber for receiving a working fluid to form a fluid column, the length of the fluid column being equal to the total length of the elongate chambers of the or each drill rod;
a displacement excitation device arranged at a proximal end of the fluid column and configured to excite the fluid column to cause the working fluid in the fluid column to oscillate, wherein the excitation device is configured to excite the fluid column at an excitation frequency at or within 10% of a natural frequency of the fluid column determined based on the fluid column having a fixed boundary condition at the proximal end thereof; and
a tool piston moveably mounted at a distal end of the fluid column and a drilling tool connected to the tool piston such that the oscillation of the working fluid in the fluid column imparts an oscillating force to the drilling tool.
In preferred embodiments, the excitation frequency is at or within 5% of the natural frequency of the fluid column. Ideally, the excitation frequency is within 1% of the natural frequency of the fluid column. The closer the excitation frequency is to a natural frequency of the fluid column, the closer operation of the device is to resonance. Excitation frequencies within 10% of a natural frequency of the fluid column cause displacement of fluid in the fluid column with an amplitude large enough to allow sufficient force to be imparted to the drilling tool to produce or enhance a drilling action.
The drilling device may be considered to be a down-the-hole drilling device, since the tool piston is arranged in the drilled hole during drilling.
A fluid column has a number of natural frequencies that are a function of the properties 30 of the fluid, the length of the column and the boundary conditions applied to the column. In the present case, the natural frequencies are determined based on the fluid column having a fixed boundary condition at its proximal end; that is, no displacement or flow of fluid occurs at the proximal or driver end of the fluid column (relative to the end walls of the column).
Generally, where a stiffness of the fluid is lower than a stiffness of the rock-tool interaction, the distal end of the fluid column may also be considered to have a substantially fixed boundary condition. Assuming a fixed-fixed boundary condition, the natural frequencies of the fluid column can be determined using the equation:
where fn is the natural frequency, k is the order of the natural frequency, L is the length of the fluid column, Bfluid is a fluid bulk modulus and PFluid is fluid density.
In situations where the stiffness of the rock-tool interaction has a very low value such that it does not correspond to a fixed boundary condition at the distal end of the column, this can be accounted for using frequency control mechanisms discussed below.
In order to cause oscillation of the working fluid in the fluid column, an excitation must be introduced. According to the present invention, a displacement excitation device is arranged at a proximal end of the fluid column and configured to excite the fluid column to cause the working fluid in the fluid column to oscillate. The displacement excitation device may introduce excitation by reciprocally displacing a proximal end wall of the chamber (of the drill rod, or the most proximal drill rod) in a longitudinal direction of the chamber, or otherwise changing the volume of the fluid column in a reciprocal manner.
Resonance occurs in the fluid column when the excitation frequency and the natural frequency of the fluid column coincide. Exciting the fluid column at an excitation frequency at or close to a natural frequency of the fluid column therefore allows the system to operate at or close to resonance so that the amplitude of the displacement of the fluid in the fluid column will grow substantially. Likewise, the pressure oscillation in the fluid column will have high amplitudes. This allows the impulse associated with the force imparted to the drilling tool to be maximised.
Impulse generators for percussion tools have been suggested, in which the natural frequency of the system is determined using a free boundary condition at the proximal end of a fluid column. In such systems, the excitation is introduced by way of a force or pressure excitation at the proximal end of the fluid chamber. A small amplitude pressure excitation at the proximal end of the chamber creates a large fluid displacement at the proximal end (displacement antinode) and a large pressure amplitude at the distal end (pressure antinode). The large fluid displacement at the proximal end leads to a very high flow requirement as high volumes of fluid are required to move in and out of the fluid column. Thus, such systems only require a small pressure variation but must be capable of delivering high flow rates.
The drilling device of the present invention is advantageous in that it includes a displacement excitation device. This type of excitation device creates a high pressure amplitude at the proximal end (and correspondingly at the distal end) of the fluid column, but requires a much lower peak fluid flow rate. The present invention therefore allows for a more compact and cheaper system and encounters much lower fluid-flow related power losses than a system which has a free boundary condition at the proximal end.
Generally, the chamber is for receiving a liquid to form the fluid column; that is, the working fluid in the fluid column is a liquid. The type of liquid used does not have a significant impact on the performance of the drilling device, since the natural frequency of the fluid column is based on the properties of the liquid used. In certain embodiments, the liquid is hydraulic oil. Hydraulic oil is suitable for single pass drilling applications; that is, where drill rods are not added or removed while drilling the hole. Generally, sealing of the device at the distal end is advantageous to avoid leakage of working fluid. Where oil is used in a single pass device, a radial seal may be easily implemented at the distal end of the device, due to the high viscosity and good lubrication properties of hydraulic oil. However, for extension drilling, where additional drill rods are added to the drilling device or drill string as the hole gets deeper, there is a risk of oil leakage from the fluid column as new rods are added. Introducing a valve arrangement for the individual drill rods to prevent oil leakage would interfere with the oscillation of the fluid column.
In other embodiments, the liquid is water. Water is particularly suitable for extension drilling applications since it is harmless to the environment, and leakage when adding or removing drill rods is therefore not a concern. However, water leakage via a clearance between the first cylindrical wall and the tool piston at the distal end of the device may be an issue as sealing around the tool piston may be challenging.
The drilling device may further comprise at least one outlet for water at a distal end of the fluid column and means for pumping water into the fluid column at an input flow rate, such that the water flows along a leakage fluid path between the first cylindrical wall and the tool piston and out of the at least one outlet at a leakage flow rate equal to the input flow rate. In this way, the leakage of water between the cylindrical wall and the tool piston may be used either to flush the hole, or to suppress dust generated when another flushing fluid such as air is used to flush the drilled hole. This also has the advantage of not requiring a seal at the tool piston.
In one embodiment, the or each drill rod comprises a second cylindrical wall arranged outside at least a portion of the first cylindrical wall such that an annular flushing channel is defined between the first and second cylindrical walls and the annular flushing channel is configured to receive a flushing fluid at a proximal end thereof and discharge the flushing fluid at a distal end thereof. In this embodiment, the outlet may be provided at a distal end of the fluid column, adjacent the distal end of the flushing channel.
This allows the leakage water to be used to suppress dust generated when the flushing fluid is, for example, air. The dust created by the use of air as a flushing fluid may cause significant problems. Leakage of water from the fluid column is therefore leveraged to suppress the dust, without requiring a separate water supply. Water is pumped into the fluid column at an input flow rate equal to the leakage flow rate required for dust suppression. In conventional rotary drilling, where water is injected into the flushing air for dust suppression, it enters the bearings of the tricone cutters and and washes away the bearing lubricant. However, in this embodiment the outlet for the leakage water is at a distal end of the fluid column, but rearward of the drill bit so that the water does not enter the cutter bearing section of the bit.
In another embodiment, the outlet is provided at a distal face of the drilling tool. This allows the water itself to be used as a flushing fluid. The input flow rate and the tool piston dimensions are selected such that the leakage flow rate is sufficient for flushing.
In both embodiments, extension drilling is straightforward. Preferably, each elongate chamber has a length/and the length of the fluid column L is an integer multiple of l. The water in the fluid column may be allowed to drain out when adding or removing drill rods and the device is then refilled with water before drilling is restarted. Because each drill rod has the same length l, addition or removal of a drill rod does not require a change to the excitation frequency. Where the excitation frequency is chosen as the kth natural frequency of a drilling device with a fluid column of length l, then where N drill rods of length l are used, the excitation frequency becomes the N*kth natural frequency of the drilling device with a fluid column of length L=N*l.
The displacement excitation device may be arranged to reciprocally move the fluid in the fluid column in a longitudinal direction.
In one embodiment, the displacement excitation device comprises an excitation piston disposed in a proximal end of the chamber such that a forward end of the excitation piston forms a proximal end wall of the fluid column. The excitation piston is coupled to a crankshaft mechanism such that the piston is driveable reciprocally in a longitudinal direction of the fluid column to reciprocally displace the proximal end wall of the fluid column.
In another embodiment, the displacement excitation device comprises a cam mechanism arranged at a proximal end of the chamber such that each of a plurality of pistons is driveable reciprocally in a radial direction by a rotatable cam, to change the volume of the chamber in which the fluid column is established in a reciprocal fashion.
In another embodiment, the displacement excitation device comprises an epicycloid mechanism comprising a multi-lobed rotor having N lobes arranged to orbit within a multi-lobed stator having N+1 lobes, such that N+1 cavities of varying volume are created between the rotor and the stator, and wherein a first group of the N+1 cavities are in fluid communication with each other and with the chamber to change the volume of the chamber in which the fluid column is established in a reciprocal manner. A second group of the N+1 cavities may be in fluid communication with each other and connected to a source of fluid at a substantially constant pressure. This reduces the pressure forces to which the rotor is subjected during operation.
The device 1 further includes a displacement excitation device 5 arranged at a proximal end 6 of the fluid column. In the embodiment shown in
where fn is the natural frequency, k is the order of the natural frequency, L is the length of the fluid column, Bfluid is a fluid bulk modulus and pfluid is fluid density. Selection of the excitation frequency is described in more detail in relation to
The drilling device 1 further comprises a tool piston 7 moveably mounted at a distal end 8 of the fluid column and a drilling tool 9 connected to the tool piston such that the oscillation of the working fluid in the fluid column imparts an oscillating force to the drilling tool. In the embodiment shown in
Due to the pressure oscillation in the fluid column, the force on the tool piston and thus, the drilling tool, will oscillate accordingly. Where the drilling device is a rotary drilling device, as shown in
The drilling device 1 further comprises a plurality of injection holes 15 for water at a distal end 8 of the first cylindrical wall 3, adjacent the distal end 14 of the flushing channel. The device 1 also comprises a pump 16 for pumping water into a proximal end 6 of the fluid column at an input flow rate. A check valve 17 is provided to prevent back flow and a seal 23 is provided at the excitation device 5 to prevent leakage of water from the proximal end of the drilling device. As shown in
In use, flushing air is supplied to the flushing channel and discharged into the drilled hole through the drilling tool to evacuate cuttings from the drilled hole. Water is supplied to the fluid column at an input flow rate and water pressure at the tool 9 induces leakage through the clearance between the piston 7 and the first cylindrical wall 3. This leakage water enters the drilled hole via the injection holes 15 in the wall 3, where it mixes with the flushing air and drill cuttings, providing dust suppression. The leakage flow is dependent on the length Lleak of the leakage fluid path. The shorter the length of the path, the higher the leakage flow rate. If more water is pumped in by the pump 16 than is leaking out, the tool piston 7 will be pushed out in a distal direction, thereby maintaining a constant static pressure in the fluid column. This, in turn, decreases the length of the leakage path Lleak, increasing the leakage flow rate so that the tool piston 7 is automatically driven to a position where the leakage flow rate is the same as the input flow rate.
Another embodiment is shown in
As in the previous embodiment, in use, water is supplied to the fluid column at an input flow rate and water pressure at the tool 9 induces leakage through the clearance between the piston 7 and the cylindrical wall 3. This leakage water enters the drilled hole via the outlet 20 in the cutting face of the tool, where it is used to flush cuttings from the hole. As before, the leakage flow is dependent on the length Lleak of the leakage fluid path. The shorter the length of the path, the higher the leakage flow rate. If more water is pumped in by the pump 16 than is leaking out, the tool piston 7 will be pushed out in a distal direction thereby maintaining a constant static pressure in the fluid column. This, in turn, decreases the length of the leakage path Lleak, increasing the leakage flow rate so that the tool piston 7 is automatically driven to a position where the leakage flow rate is the same as the input flow rate.
A further embodiment of the invention is shown in
The device 1 further includes a displacement excitation device 5 arranged at a proximal end 6 of the fluid column. In the embodiment shown in
In this embodiment, an inner flushing channel or pipe 11 defined by the inner cylindrical wall 10′ is configured to receive a flushing fluid, such as air, at a proximal end 12 thereof via inlet 13 and discharge the flushing fluid through outlets in a distal face 21 of the drilling tool 9. In use, flushing air is supplied to the flushing channel and discharged into the drilled hole through the drilling tool to evacuate cuttings from the drilled hole. Where the working fluid is water, a leakage flow of water may be provided, similar to the arrangements described above. Where the working fluid is oil or another fluid, there is no leakage of working fluid from the chamber.
In the embodiment shown in
The arrangement of the stator and the rotor is such that N+1, or in this case, six cavities are formed between them as the rotor rotates. The volume of each cavity changes in a harmonic fashion with a frequency ωorbit. When used as a motor, each of these cavities is connected to high and low pressure lines with a valve system such that the cavity receives high pressure liquid when the cavity volume is increasing and the cavity is connected to a low pressure line when the cavity volume is decreasing. When used as an excitation mechanism, as in the present application, the cavities are divided into two sets, labelled A and B, respectively in
An alternative drive arrangement for the rotor 30 is shown in
In the embodiments described above in relation to
Fmax=pmax*Apressure
Fmin=pmin*Apressure,
where pmin and pmax are the maximum and minimum pressures in the fluid column and Apressure is the area upon which the pressure is acting. In an alternate embodiment, the second set of cavities may be connected to a constant pressure source with a pressure equal to the mean pressure of the fluid column, pmean. This reduces pressure forces on the rotor substantially:
Fmax=(pmax-pmean)*Apressure
Fmin=−(pmean-pmin)*Apressure, or
Fmax/min=±(pamp)*Apressure,
where pamp is pressure oscillation amplitude in the fluid column. Thus, the maximum force on the rotor is at least 50% lower than in the case where the second set of cavities is not connected to a pressure source. The constant pressure source may be provided by a gas accumulator 41 connected to the B cavities, as shown in
Further examples of control arrangements for the system shown in
The words “comprises/comprising” and the words “having/including” when used herein with reference to the present invention are used to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.
It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.
Number | Date | Country | Kind |
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S2020/0253 | Nov 2020 | IE | national |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2021/080802 | 11/5/2021 | WO |