LUBRICATION SYSTEM FOR A DRILLING APPARATUS

Abstract

The present invention provides a lubrication system for a drilling apparatus. The drilling apparatus includes a drill string and a drill bit, and it is driven by a working fluid circulated through a working fluid circuit. The lubrication system uses a reservoir of a lubricating fluid for supply to a drilling apparatus during a drilling operation; and a pump for supplying lubricating fluid from said reservoir to the drilling apparatus during the drilling operation. The pump is controlled to supply lubricating fluid from the reservoir at a determined rate to a lubrication circuit formed by the working fluid circuit of the drilling apparatus.

Description

FIELD OF THE INVENTION

This invention relates to a lubrication system for a drilling apparatus.

BACKGROUND TO THE INVENTION

Drilling apparatus are used in exploitation of mineral resources. Reverse circulation drilling apparatus are used in exploration and normal circulation drilling apparatus are used for mining and exploration applications. Drilling of blastholes and geological sampling are just two applications for such drilling apparatus which is typically subjected to very severe operating conditions. The drilling apparatus may be rotary or percussive.

A percussive drilling apparatus, such as a hammer, comprises a drill string having, at its working end, a drill bit mounted in a drive sub. The drilling apparatus is powered by a working fluid, typically compressed air, the pressure of which is used to drive a drill bit, whilst the drill string is rotating, to impact and drill a formation. To this end, such drilling apparatus has a working fluid circulation system for directing working fluid from the compressor through the drilling apparatus to the drill bit from which spent working fluid is exhausted. Such working fluid circulation system or circuit may be complex. Driving action is caused by fluctuations in working fluid pressure which drive a piston, in a working chamber forming part of the working fluid circuit, to impact the drill bit and generate drilling action and product cuttings which are recovered, in a flushing and/or exhaust flow, as required. Reciprocation of the piston generates considerable friction and potential for wear. Other parts of the drilling apparatus are also likely subject to wear.

To date, despite the operating conditions to which a drilling apparatus is subjected, lubrication practice has typically involved cracking, or opening, of the drill string—at an operator selected point—and pouring of lubricant into the drill string. This lubricant then finds its way through the working fluid circulation system, which typically forms the lubricant circuit for drilling in accordance with this lubrication practice, and to the working end of the drilling apparatus. Such lubrication practice, while surprisingly effective in the short term, is unlikely to allow for the correct quantities of, or rates of supply of, lubricant to be applied to the drilling apparatus.

In percussive drilling, wear damage and component failure, including drill bit failure through shanking of a drill bit, will result if insufficient lubricant is supplied. Even if failure is avoided, insufficient lubrication may prevent sealing within the working fluid circuit, for example between piston and working chamber walls as defined by wear sleeve or inner cylinder if an inner cylinder accommodates the piston. In the case of sub-optimal sealing, drilling efficiency is reduced.

If too much lubricant is supplied, drilling apparatus operation may be otherwise affected and there is some cost impact as well. However, subject to avoidance of “dieseling” where lubricating fluid in excessive quantity ignites, supply of too much lubricant is generally less of a problem than supply of too little.

Current drilling apparatus lubrication practice involving drill string “cracking” therefore interferes with drilling operations whilst presenting a hazard to the operator. Lubrication, by definition, is required whilst a drilling apparatus is operating. This means that the operator is working whilst machinery is in operation and this presents obvious hazard.

Current practice in drilling presents both disadvantages of potentially insufficient lubrication of the drilling apparatus and sub-optimal drilling efficiency whilst hazard exists for the operator applying the lubricant.

U.S. Pat. No. 4,508,183 describes a method and apparatus for providing a flow of lubricating fluid from a surface mounted lubricating fluid source through a rotatable drill pipe to rotary cutting cones of a rotary drill bit for drilling in an underground formation, including pump means for providing a flow of lubricating fluid from the fluid source to an end of the drill pipe. Drill pipe conduit means extending along the length of the drill pipe is provided for receiving the flow of lubricating fluid and for directing the lubricating fluid flow along the drill pipe to the drill bit. The drill pipe conduit means is a galley line included within the wall of the drill pipe of each section of drill pipe. The galley line extends from the upper end to the lower end of each drill pipe and may be formed by casting or machining a keyway or slot along most of the drill pipe section. A suitably sized elongated cover member may then be fixed welded in place along the surface of the drill pipe wall to fill in a portion of the slot and to turn the slot into an enclosed conduit. Distribution conduit means at the drill bit extends from the drill pipe conduit means to the cutting cones and receives the flow of lubricating fluid from the drill pipe conduit means for directing the lubricating fluid flow to the cutting cones for lubrication.

US 2011/0031018 describes a horizontal direction drilling system comprising a power pack coupled to a source of compressed air and a water reservoir and forms a mixture of compressed air, water and oil. The horizontal direction drilling system further comprises a steerable horizontal drill. The steerable horizontal drill includes an air powered reciprocating hammer, and a drill head. The steerable horizontal drill receives the mixture to power the reciprocating hammer. The drill bit includes a drill face and the mixture exits the steerable horizontal drill through the drill face. The amount of lubricant and water can be respectively controlled to control the proportions in the mixture powering the reciprocating hammer. Horizontal directional drilling (HDD) is commonly used for routing utilities through pipes, ducts and cables through underground impediments such as rock structures. To that end the hammer includes a sonde to identify position and orientation of the drill so that it can be steered.

It is an object of the present invention to provide a lubrication system to improve the lubrication and drilling efficiency of earth drilling apparatus.

SUMMARY OF THE INVENTION

With this object in view, the present invention provides a lubrication system for an earth drilling apparatus including a drill string and a drill bit, said drilling apparatus being driven by a working fluid circulated through a working fluid circuit comprising:

a reservoir of a lubricating fluid for supply to a drilling apparatus during a drilling operation; and
a pump for supplying lubricating fluid from said reservoir to said drilling apparatus during said drilling operation,
wherein said pump is controlled to supply lubricating fluid from the reservoir at a determined rate to a lubrication circuit formed by said working fluid circuit of said drilling apparatus.

The lubrication system may be used in percussion drilling apparatus or rotary drilling apparatus.

In another aspect of the invention, there is provided a method of drilling a formation with an earth drilling apparatus having a drill string comprising a drill bit, said drilling apparatus being driven by a working fluid circulated through a working fluid circuit of said drilling apparatus comprising lubricating the drilling apparatus during a drilling operation wherein said drilling apparatus comprises a lubrication system having a reservoir of a lubricating fluid for lubricating the drilling apparatus; and a pump for supplying lubricating fluid from said reservoir to said drilling apparatus during said drilling operation wherein said pump is controlled to supply lubricating fluid from the reservoir at a determined rate to a lubrication circuit formed by said working fluid circuit of said drilling apparatus.

The drilling apparatus is conveniently operated from a drilling rig, the drilling rig comprising equipment items, such as air compressor, hoisting equipment, hydraulics and other accessories for operating the drilling apparatus. The drilling rig is surface located and the piston pump and lubricating fluid reservoir of the lubrication system are conveniently and advantageously surface located also, advantageously, on a deck of the drilling rig. This allows easier servicing of the pump, if required, and filling of the lubricating fluid reservoir when required.

A conventional working fluid for drilling apparatus is compressed air. In such case, live compressed air may be supplied through a working fluid circuit extending from an air compressor, also conveniently located on any drilling rig, through a check valve, and choke if provided for control of exhaust fluid flow rate for flushing cuttings, and through the drill string to its working end located at the base of a hole being drilled. It is not envisaged that water would be commonly used as working fluid for the drilling apparatus.

The working fluid circuit must provide working fluid to a working chamber located within the drilling apparatus to operate a reciprocating piston within the drill string near its working end. As the piston reciprocates in its working chamber in response to cyclic pressure variations in volumes above and below the piston in the working chamber, it impacts the drill bit at high frequency to fracture material into cuttings. The working fluid pressurises a drive volume of the working chamber when driving the piston, in a drive stroke, to impact the drill bit. Working fluid is then exhausted from the working fluid circuit through or past the drill bit to flush cuttings away from the cutting face of the drill bit in a flushing flow. Following impact of piston on drill bit, working fluid pressurises a return volume of the working chamber to drive the piston, in a return stroke, back to the top of the working chamber in preparation for a further drive stroke. Working fluid is also exhausted through or past the drill bit during the return stroke.

The system and method of the invention involve entraining a determined amount of lubricant within the working fluid. This may atomise the lubricant to provide more beneficial lubricating effects. The working fluid circuit, as for example above described, therefore forms the lubrication circuit for the drilling apparatus. The above description of the working fluid circuit is generalised and other working fluid circuit configurations, though including the same essential elements, may be adopted by those skilled in the art. The system and method of the invention do not require fabrication of drilling apparatus components to include conduits solely for delivering lubricant to the drilling apparatus. The system and method are therefore conveniently, and cost effectively, applied to conventional drilling apparatus.

The lubricating fluid includes a lubricant used to lubricate the drilling apparatus and especially moving parts thereof. Such lubricants may be described as rock oils and are selected for the drilling application.

Though many components of a drilling apparatus require lubrication, as important examples, lubricant must be supplied to a drill bit/drive sub assembly connected to the drill string to avoid drill bit/drive sub failure as well as to the piston for driving the drill bit. Typically, the drill bit and drive sub are provided with respective and complementary spline portions formed about their perimeter. A plurality of spline portions are provided on both drill bit outer or shank surface and drive sub inner surface which interlock to form the drill bit/drive sub assembly. The assembly allows the drill bit to slide (though not rotate) relative to the drive sub. Lubrication at the spline portions is important to prevent seizing and other forms of failure collectively known as “shanking”. The lubricant pump therefore delivers lubricant at sufficient rate to form a film on these complementary drill bit and drive sub spline portion surfaces. Spaces between the interlocking spline portions act as channels for working fluid to pass through to the cutting end of the drill bit so also forming part of the working fluid circuit and lubrication circuit in this type of drilling apparatus.

Lubricating fluid is also used to create an oil seal between a piston where used for driving the drill bit and the wall of the piston working chamber. The working chamber wall may be formed by the inner wall of a wear sleeve or the inner wall of an inner cylinder located within the wear sleeve. This oil seal is required to significantly reduce or avoid working fluid leakage between drive and return volumes of the working chamber. An effective oil seal increases pressurisation of drive and return volumes of the working chamber on drive and return strokes respectively and optimises drilling efficiency as measured by penetration rate.

The lubricating fluid may also include foams, detergents and other agents, particularly surface active agents, for assisting drilling operations and is used, in this specification, with that sense. Foams, in particular, are often used to assist air drilling operations by assisting with cuttings removal in flushing air flows. Such foams may be corrosive.

The lubrication system may be used to supply a plurality of lubricating fluids in which case it may conveniently include a plurality of reservoirs, each reservoir corresponding with a particular lubricating fluid. For example, one reservoir could contain foam and another reservoir, a lubricant.

The determined rate of supply of lubricating fluid to the drilling apparatus may depend on one or more of a plurality of factors including drill string or hammer diameter, formation type (which influences drilling apparatus operating conditions) and drilling apparatus working fluid pressure, typically compressed air pressure. Other factors may also be relevant.

The pump is conveniently, and advantageously, a hydraulically operated pump. Hydraulic fluids, such as hydraulic oils, may be used to drive the pump using a timer or control valve device for controlling hydraulic fluid pressure within the pump (and, consequently, delivery pressure of the lubricating fluid to the drilling apparatus), cycle time and lubricating fluid supply frequency and rate. Pressure regulators may be included in the lubrication system to reduce hydraulic fluid pressures to suitable levels for operation of the pump, it being understood that hydraulic fluids used for drilling operations, and sourced from hydraulic fluid pumps conveniently located on drill rigs, are typically at high pressure, higher than required to drive the pump of the presently described lubrication system.

The pump is advantageously a piston pump which draws a predetermined quantity of lubricating fluid from the lubricating fluid reservoir on an intake stroke of the pump and expels it on an exhaust or delivery stroke to the drilling apparatus. The stroke refers to the movement of a piston within a working chamber of the pump. The working chamber may comprise two variable volume chambers, one on the delivery side of the pump and the other on the pump side. The pump side chamber is pressurized by a hydraulic fluid for operating the pump during a delivery stroke. The stroke or length of travel of the piston may also be controlled to control rate of intake of lubricating fluid into the hydraulic side chamber and supply of lubricating fluid to the drilling apparatus. Alternatively, a diaphragm pump could be used.

The pump is connected, through a lubricating fluid system, both to the lubricating fluid reservoir and to the drilling apparatus. Return of lubricating fluid to the reservoir during a pump delivery stroke or to the drilling apparatus on an intake stroke should be prevented. To this end, the lubricating fluid system may be provided with check or non-return valve(s) in supply and delivery lines to prevent return of lubricating fluid to the reservoir when supply to the drilling apparatus is intended or to the drilling apparatus, in uncontrolled manner, when supply to the pump is required in an intake stroke.

BRIEF DESCRIPTION OF THE DRAWINGS

The lubrication system for a drilling apparatus of the present invention may be more fully understood from the following description of a preferred non-limiting embodiment made with reference to the accompanying drawings in which:

FIG. 1 is a perspective view of the lubrication system for drilling apparatus of one embodiment of the present invention.

FIG. 2 is a side view of the lubrication system of FIG. 1.

FIG. 3 is a top view of the lubrication system of FIGS. 1 and 2.

FIG. 4 is an end view of the lubrication system of FIGS. 1 to 3.

FIG. 5 is a section view of the pump included within the lubrication system of FIGS. 1 to 5.

FIG. 6 is an exploded view of the pump included within the lubrication system of FIGS. 1 to 5.

FIG. 7 is a side section view of a drilling apparatus lubricated using the lubrication system of one embodiment of the present invention.

FIG. 8a is a section view of the drilling apparatus along section line A-A of FIG. 7 and showing the drill bit/drive sub assembly.

FIG. 8b is a enlarged view of the drilling apparatus showing detail B of FIG. 8a.

FIG. 9 is a side view of the drill bit included within the drilling apparatus as illustrated in FIGS. 7 and 8.

FIG. 10 is a perspective view of the drive sub included within the drilling apparatus as illustrated in FIGS. 7 and 8.

DESCRIPTION OF PREFERRED EMBODIMENT

Referring to FIGS. 1 to 10, there is shown a lubrication system 10 for a drilling apparatus. The drilling apparatus is shown in FIGS. 7 to 10 which illustrate a percussive drilling apparatus in the form of a normal circulation down the hole (DTH) hammer 100 including a drill bit 130. Drill bit 130 has, viewed rearwardly along its length, a head portion 130a and a shank 130c with an intermediate portion 130b and a cylindrical portion 130d. Cylindrical portion 130d is relatively short in comparison to the length of the intermediate portion 130b of shank 130c. Head portion 130a includes a cutting face 311. The surface of intermediate portion 130b of drill bit 130 is formed with a plurality of spline portions 131 correspondent with and, and interlocked with, respective and complementary driving spline portions 128 of a drive sub 120 forming a further part of DTH hammer 100. The drill bit 130 can slide relative to the drive sub 120 but not rotate relative to it. Spaces 136 are left between the spline portions 128 and 131.

DTH hammer 100 includes a wear sleeve 110 which, near the working end of DTH hammer 100, is located a working chamber 144 provided with a piston 150. Live compressed air is supplied from a compressor (not shown) of the DTH hammer 100 and through a compressed air (working fluid) circuit delivering compressed air to 1) operate the piston 150 and 2) flush cuttings away from the cutting face 311 of drill bit 130 with assistance of a foam. This compressed air is the working fluid for DTH hammer 100. Compressed air flows through the compressed air circuit extending from the compressor 195, check valve 155 in top sub 152, through central passageway 153 of top sub 152 and through a further portion of the compressed air circuit to working chamber 144 to operate the piston 150. The compressed air circuit extending downstream of piston 150 is described below.

Piston 150 reciprocates in the working chamber 144 in response to cyclic variations in the pressure of drive and return volumes 144a and 144b of the working chamber 144. On drive strokes, piston 150 impacts the drill bit 130 at high frequency. As drill bit head portion 130a, provided with round headed cutter elements or buttons 135 of tungsten carbide or other suitable material, impacts the bottom of a hole during a drilling operation, cuttings are formed and returned to the surface entrained in exhaust air from the compressed air circuit. At least portion of this exhaust air is delivered from working chamber 144 depending on choke arrangements (if used).

Compressed air pressurises drive volume 144a of the working chamber 144 when driving the piston 150, in a drive stroke, to impact the drill bit 130. Compressed air is then exhausted from the drive volume 144a through a downstream portion of the compressed air circuit extending from drive volume 144a and through the spaces 136 between the spline portions 128 and 131.to finally exit past the drill bit 130.

Following impact of piston 150 on drill bit 130, compressed air pressurises return volume 144b of the working chamber 144 to drive the piston 150, in a return stroke, back to the top of the working chamber 144 in preparation for a further drive stroke. Compressed air is also exhausted through the above described downstream portion of the compressed air circuit during the return stroke.

DTH hammer 100 requires lubrication of its moving parts by a lubricating fluid such as a rock oil. Lubrication at the spline portions 128 and 131 of the drill bit/drive sub assembly 125, and the spaces 136 between them, is particularly important to prevent seizing and other forms of failure collectively known as “shanking”. Lubricant is required in sufficient quantity to form an effective lubricating film on these complementary drill bit and drive sub spline portion 128, 131 surfaces. Attempting to deliver lubricant only by the “cracking” method, and pouring lubricant into the drill string of DTH hammer 100 cannot ensure that this requirement is achieved.

Lubricating fluid is also required to form an oil seal between the inner wall of wear sleeve 110 and piston 150, that is, an oil film on wall surfaces defining the working chamber 144 of the DTH hammer 100. This oil seal is required to significantly reduce or avoid compressed air leakage between drive and return volumes 144a, 144b of the working chamber 144. An effective oil seal increases pressurisation of drive and return volumes 144a, 144b of the working chamber 144 on drive and return strokes respectively and optimises drilling efficiency as measured by penetration rate.

Check valve 155, regulating compressed air flow to the drill bit/drive sub assembly 125, is another component lubricated by the lubrication system.

Lubrication system 10 ensures that the objectives of lubrication and sealing to promote drilling efficiency of are effectively achieved.

Referring now to FIGS. 1 to 6, lubrication system 10 includes a reservoir 20 of lubricating fluid for supply to DTH hammer 100 during a drilling operation. Reservoir 20 is a plastic tank with 30 litre capacity (in the example shown; reservoir 20 may have any desired capacity dependent on the lubricating fluid to be supplied) and it may contain, as lubricating fluid, a foam or detergent for assisting air drilling operations. A suitable plastic, such as HDPE, is selected for corrosion resistance as foams and detergents are often corrosive. It may also, as here, include a lubricant being a rock oil of required specification for use in lubrication of the moving parts of the drilling apparatus and notably the drill bit/drive sub assembly and the piston 150 for driving drill bit 130 during a drilling operation. Tank 20 is provided with a plastic cap 22 which can be removed to enable top up of lubricating fluid as required.

Lubrication system 10 includes a pump 30 for automatically supplying the lubricating fluid from tank 20 to the DTH hammer 100 during a drilling operation. Pump 30 is controlled to supply lubricating fluid from plastic tank 20 at a determined rate to the lubrication circuit of the DTH hammer 100. It may be understood, from the above description, requiring that lubricant be supplied to the working chamber 144 and drill bit/drive sub assembly 125, that this lubrication circuit corresponds with the compressed air circuit used for operating the DTH hammer 100.

The reservoir 20 and pump 30 are located within a housing 10a of the lubrication system 10 surface located on a drilling deck 290 of a drilling rig (not shown) used for operating DTH hammer 100. The lubrication system housing 10a is bolted to this deck by bolts 83a located at mounting plates 83 of the lubrication system 10. The housing 10a may readily be disconnected, removed for maintenance and replaced by a further housing 10a, if necessary.

Pump 30 is hydraulically operated using a supply of hydraulic oil at predetermined pressure to drive a double sided piston 34 having two piston heads 34a and 34d connected by a rod 34b and fixed with a nut 49. The hydraulic oil may be supplied from the hydraulic equipment of the drilling rig and may be different to the rock oil used for lubrication of DTH hammer 100.

As seen most conveniently in FIGS. 5 and 6, pump 30 has a cylindrical housing 31 comprised of two cylindrical housing portions 31a and 31b each threadably connected to a gland centre 34c spacing portions 31a and 31b. Gland centre 34c includes a bush 48 to provide a seal for piston rod 34b at the gland centre 34c. Gland centre 34c also acts as a limit to travel or stroke of piston head 34a.

The cylindrical housing 31 of pump 30 contains a working chamber. On its pump side and within cylindrical housing portion 31b, is contained a variable volume chamber 32 with a lubricating fluid port 33 through which lubricating fluid is supplied to and from the pump 30 toward DTH hammer 100. A breather 38 is also provided for chamber 32. On the hydraulic side and within cylindrical housing portion 31a is contained a variable volume chamber 35 with a hydraulic oil inlet 36 formed in pump end gland 46 for supplying hydraulic oil to drive pump 30 and a hydraulic oil outlet 37 for discharging hydraulic oil from pump 30 following a lubricating fluid supply event. Chambers 32 and 35 are shown separated by reciprocating piston 34 and the chambers 32 and 35 vary in volume depending on piston 34 position within cylindrical housing 31.

Piston 34 moves in one direction (to the left in FIG. 5) to deliver lubricating fluid from pump 30 to DTH hammer 100 when required on a lubricating fluid delivery stroke. Then, when lubricating fluid has been delivered from pump 30 to the drilling apparatus and hydraulic oil—used in driving the piston 34—has been vented from pump 30 through oil outlet 37 and line 39, the piston 34 moves in the opposite direction (to the right in FIG. 5) creating suction in chamber 32 and enabling lubricating fluid to be drawn from tank 20 into chamber 32 on an intake stroke. Hydraulic oil is not supplied to chamber 35 during the intake stroke of piston 34.

When delivery of a further quantity of lubricating fluid to the drilling apparatus is required, hydraulic oil is supplied from the hydraulic oil supply through supply hose 42 and onward through supply duct 44 to chamber 35. This supply of hydraulic oil causes piston 34 to move, in a delivery stroke, to drive lubricating fluid from chamber 32 towards DTH hammer 100. Intake and delivery stroke timing are separated by controlled time duration, regardless of any lag before piston 34 starts to move to draw lubricating fluid into chamber 32. This controlled time duration, necessary to achieve determined lubricant supply rate, is likely to be in the order of seconds. However, longer duration is possible dependent on lubricating fluid requirements of the DTH hammer 100 and drilling conditions which influence these requirements. Higher rated rock oils may be required as lubricating fluids as drilling conditions become more demanding. For example, drilling of a harder rock formation is likely to require higher rated rock oils at higher rates than when drilling of a soft rock formation.

Pump 30 operation has cycle time comprised of time for intake of lubricating fluid into chamber 32; time for building hydraulic oil pressure in chamber 35 for driving piston 34 to deliver lubricating fluid through port 33 towards the drilling apparatus; and time for delivering lubricating fluid through port 33 in a delivery stroke. The cycle time is controlled using a three way solenoid actuated or ON/OFF hydraulic oil control valve 40 which is connected to hydraulic oil supply hose 42 (rated to 400 Bar) and both to the hydraulic oil inlet 36 and hydraulic oil outlet 37 of pump 30. Hydraulic oil control valve 40 may be connected to an AC or DC source of electricity. Both may be made available on the drilling rig.

The energisation and de-energisation of the solenoid of hydraulic oil control valve 40 creates a pulsed supply of hydraulic oil through hydraulic oil supply duct 44 to chamber 35 of pump 30 determining the rate of supply of lubricating fluid to the drilling apparatus. Operation of the solenoid also controls venting of hydraulic oil through breather 38 and line 39.

An operator of the drill rig and lubrication system 10 may set the duration and frequency of hydraulic oil pulses to the pump 30 through hydraulic oil control valve or timer 40. These settings determine the frequency and rate of lubricating fluid supply, in pulses, to the drilling apparatus. Frequency and rate of lubricating fluid supply depends on the nature of the drilling apparatus. Larger diameter hammers generally have higher lubricating fluid requirements than smaller diameter hammers of the same design. Noting this, the capacity of tank 20 can also be selected with reference to size of the drilling apparatus. As above noted, and for purposes of illustration:

• • tank 20 capacity is 30 litres.
  • pump 30 may deliver a flow rate of between 0 and 3 litres per minute of lubricating fluid with 375 ml per delivery stroke at 510 psi
  • lubricating fluid (here a lubricant) is delivered at a supply pressure of 700 psi/50 bar.

Once set, these parameters are typically left unchanged or constant for a given drilling operation.

Lubricating fluid is delivered to chamber 32 through a lubricating fluid duct 51 extending from an outlet 24 of tank 20 to the lubricating fluid port 33 of pump 30. Duct 51 includes a check or non-return valve 55 with a crack pressure of 1 psi (allowing ready passage of lubricating fluid towards chamber 32 on an intake or suction stroke of pump 30 but no passage of lubricating fluid back into tank 20 on a delivery stroke), a strainer 53 for filtering the lubricating fluid and a ball valve 27 enabling the duct 51 to be closed if required for servicing or other operating reasons. Duct 51 is of type 316 stainless steel for corrosion resistance.

Referring to FIGS. 1 and 2, lubricating fluid is delivered through lubricating fluid port 33 through duct 61 which includes a check valve 62, with crack pressure 1 psi (and so in open state on a lubricating fluid delivery stroke as opposed to closed state of check valve 55 at the same time) and pressure gauge 63 (maximum rated pressure 60 Bar) for monitoring lubricating fluid pressure. If lubricating fluid pressure is higher or lower than required, the drill rig operator can vary the above described settings for the hydraulic oil control valve 40 to address the problem.

Downstream of pressure gauge 63, lubricating fluid delivery duct 65 communicates with an air line 190 between compressor 195 and downstream portion of the compressed air circuit for DTH hammer 100 as above discussed with reference to FIGS. 7 to 10. This ensures entrainment of lubricating fluid in the compressed air and so the compressed air circuit also forms the lubrication circuit for the DTH hammer 100. Lubricating fluid then passes, through the above described compressed air circuit, to DTH hammer 100 and its working parts (including check valve 155 for lubrication, working chamber 144 for lubrication and forming an oil seal; and drill bit/drive sub assembly 125) as above described. As such lubricating fluid passes through the plurality of spaces 136 left between the splines 128 and 131, a film of lubricant is formed and maintained because the channels formed by spaces 136 enable working fluid with entrained lubricating fluid to pass through them and contact the surfaces of complementary interlocking spline portions 128,131 of drill bit/drive sub assembly 125. Control over operation of pump 30, as above described, provides assurance that the required lubrication of the working parts of DTH hammer 100 is achieved. Expectation of premature shanking is significantly reduced.

Ducts 61 and 65 are again of type 316 stainless steel for corrosion resistance.

Pump 30, associated hydraulic oil control valve 40 and ductwork are shown in FIGS. 1 to 4 within housing 10a. These components of lubrication system 10 may be further protected from moisture and dirt by containing housing 10a within a further protective cover (not shown). This cover, of rectangular box shape and metal fabrication, is mounted on metal rods 81 and fixed into position using nuts.

Modifications and variations to the lubrication system 10 for a drilling apparatus as described in this specification may be apparent to the skilled reader of this disclosure. Such modifications and variations are deemed within the scope of the present invention. For example, the lubrication system may be applied to other percussive drilling apparatus and is not limited only to the embodiment as described above.

Claims

1. A lubrication system for a drilling apparatus including a drill string and a drill bit, said drilling apparatus being driven by a working fluid circulated through a working fluid circuit, said system comprising: wherein said pump is controlled to supply lubricating fluid from the reservoir at a determined rate to a lubrication circuit formed by said working fluid circuit of said drilling apparatus.

a reservoir of a lubricating fluid for supply to a drilling apparatus during a drilling operation; and

a pump for supplying lubricating fluid from said reservoir to said drilling apparatus during said drilling operation,

2. A lubrication system according to claim 1, wherein said drilling apparatus is operated from a surface located drilling rig, said pump and the reservoir also being surface located, preferably on a deck of the drilling rig.

3. A lubrication system according to claim 2 wherein said working fluid is compressed air.

4. A lubrication system according to claim 2 wherein said drilling apparatus comprises an assembly of said drill bit and a drive sub, said drill bit and drive sub being provided with a plurality of respective and complementary spline portions formed about their perimeter, said spline portions interlocking to form said assembly with spaces between said interlocking spline portions acting as channels through which both working fluid and entrained lubricating fluid pass.

5. A lubrication system according to claim 4 wherein said pump delivers lubricating fluid at sufficient rate to form a film on surfaces of the complementary interlocking spline portions of said assembly of drill bit and drive sub.

6. A lubrication system according to claim 2, wherein the lubricating fluid creates an oil seal between a piston reciprocable in a working chamber within said drill string for driving said drill bit and the wall of the working chamber.

7. A lubrication system according to claim 2, wherein the determined rate of supply of lubricating fluid to said working fluid circuit depends on at least one parameter selected from the group consisting of drill string or hammer diameter, working fluid pressure and formation type.

8. A lubrication system according to claim 2 wherein said pump is a hydraulically operated pump, having hydraulic fluid pressure within the pump controlled by a timer or a control valve device for controlling hydraulic fluid pressure within the pump.

9. A lubrication system according to claim 8 including pressure regulator(s) for reducing pressure of hydraulic fluid from the drill rig to pressure suitable for operating said pump.

10. A lubrication system according to claim 8 wherein said pump is a piston pump.

11. A lubrication system according to claim 10, wherein the piston pump draws a predetermined quantity of lubricating fluid from the reservoir during intake stroke, and expels the drawn lubricating fluid during a delivery stroke to the drilling apparatus.

12. A lubrication system according to claim 11, wherein the piston pump includes a working chamber comprising two variable volume chambers, one variable volume chamber being on a delivery side of the pump, and the other variable volume chamber being on a pump side of the pump.

13. A lubrication system according to claim 12, wherein the pump side chamber is pressurised by a hydraulic fluid for operating the pump during delivery stroke.

14. A lubrication system according to claim 13, wherein length of travel of the piston of the pump is controlled to control rate of intake of hydraulic fluid into hydraulic side chamber and supply of lubricating fluid to the drilling apparatus.

15. A lubrication system according to claim 14 wherein hydraulic fluid operating the hydraulic pump is the lubricating fluid contained in the reservoir.

16. A lubrication system according to claim 13 including at least one non-return valve to prevent return of lubricating fluid to the reservoir when the lubricating fluid is intended to be supplied to the drilling apparatus, or the drilling apparatus when supply to the pump is required.

17. A lubrication system according to claim 1 wherein the drilling apparatus is a rotary drilling apparatus or a percussive drilling apparatus.

18. A method of drilling a formation with an earth drilling apparatus including a drill string and a drill bit, said drilling apparatus being driven by a working fluid circulated through a working fluid circuit, said method comprising lubricating the drilling apparatus during a drilling operation wherein said drilling apparatus comprises a lubrication system having a reservoir of a lubricating fluid for lubricating the drilling apparatus; and a pump for supplying lubricating fluid from said reservoir to said drilling apparatus during said drilling operation, said pump being controlled to supply lubricating fluid from the reservoir at a determined rate to a lubrication circuit formed by said working fluid circuit of said drilling apparatus.