AU2016266110B2 - A Reverse Circulation Down Hole Hammer - Google Patents

Abstract

A reverse circulation drill bit comprises an elongate hollow body; a cutting face; a central opening in the cutting face for receiving a cut sample; a generally cylindrically shaped tube located within a hollow portion of the body and extending substantially co-axially with the body so as to define a gap between the tube and the inside wall of the hollow body; and an annular entrance extending inwardly from the gap inside of the tube so as to direct fluid travelling through the gap towards the cutting face into the inside of the tube in a direction away from the cutting face. 2/4 C CMj C~ coo C~C, CC~) LO' (D 00 . . ......... C~C CCD CM CD

Description

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A Reverse Circulation Down Hole Hammer

Field of the Invention

[0001] The present invention relates to downhole hammers comprising percussion drill bits used for sub-surface drilling in the earth.

Background

[0002] Sub-surface drilling is used in exploration to probe sub-surface features of interest by extracting samples of the sub-surface rock, such as in exploration for a potential mine site. The extracted samples are analysed to determine the mineralogical, petrological and structural properties of the sub-surface rock to determine whether the potential mine site contains commercially viable ore deposits. In order to extract the samples, a drilling rig is used to bore a hole through the sub-surface rock in a manner that produces rock chips or cored rock.

[0003] The simplest form of exploration drilling is rotary air blast (RAB) drilling. This type of down hole drill uses a blade style bit or pneumatic reciprocating piston driven hammer to drive a drill bit to cut the drill hole. Air sent through the drill string then blows cuttings up the outside of the drill string where it is collected at the surface. This form of drilling is known to suffer from the disadvantage of contamination of the cuttings as it passes up through the borehole.

[0004] Another common form of drilling is reversing circulation (RC) drilling. This can also use a blade style bit or a pneumatic reciprocating piston driven hammer to drive a drill bit to cut the drill hole. This form of drilling utilises a dual tube drilling system comprising an outer rod and an inner tube to convey the sample to the surface. Air is blown down an annular space inside the rod and a pressure differential is used to lift cuttings up an inner tube inside of the rod. The percussive hammer utilised for RC drilling is also fitted with an inner tube that is used to convey a sample through the hammer and into the inner sample tube. This style of drilling is reliant on certain ground conditions and clearance of the drilling system to the hole being drilled to return a sample to the surface. The benefit of RC style drilling is its ability to deliver a relatively uncontaminated sample to the surface.

[0005] A type of RC drilling is Air Core (AC) drilling. An AC drilling system also utilises a two tube system consisting of an outer rod and an inner tube to convey the sample to the surface but is less reliant on ground conditions and hole clearance to return the sample as it turns the airflow around inside the bit and creates a low pressure at the bit face to draw cuttings into the inner tube. This provides the benefit that the samples are free from contaminants that other mineral exploration drilling techniques create. However, a substantial disadvantage of the known AC drilling technique is that the cutting blades are only suitable for boring through relatively soft, unconsolidated or weathered ground.

[0006] Percussive RC drill bits typically have two spaced apart openings in the cutting face of the drill bit. These openings extend within the head of the drill bit toward a central axis of the drill bit and are connected to a central passage in the drill bit. This form of drilling can suffer when drilling certain types of ground, typically transitional formations where the ground doesn't turn the airflow around so as to carry the sample into the inner tube. Difficulties are also experienced when drilling wet and sticky material that can block these openings. Also because airflow is being discharged from the hammer, some of the material to be sampled will be carried up the outside of the drill pipe and result in ineffective collection of the sample.

[0007] Despite these disadvantages, conventional thinking is that these spaced apart openings are required so as to maximise the cutting surface's contact with rock being drilled. In particular it is noteworthy that providing a central opening used in an AC drill goes against what would be normal thinking of the requirements of a percussive RC drill bit because having a central opening would not allow for cutting services of the drill bit to impact that area of rock being drilled. Conventional thinking is that all of the area of rock being drilled needs to be acted upon by the cutting surface, hence the spaced apart openings and hence various orbital placements of cutting buttons of the cutting surface.

[0008] There have been attempts to combine the concepts of AC drilling and percussive RC drilling, such as in Australian patent 592375 and Australian patent 604171. However, in both of these exhaust expelled from the pneumatic hammer mechanism is coupled with a bypass air feed to direct air into the central tube with exhaust air not being used to collect the sample.

[0009] The present invention seeks to provide an improvement or an alternative over the prior art.

[0010] In this specification the terms "comprising" or "comprises" are used inclusively and not exclusively or exhaustively.

[0011] Any references to documents that are made in this specification are not intended to be an admission that the information contained in those documents form part of the common general knowledge known to a person skilled in the field of the invention, unless explicitly stated as such.

Summary of the Invention

[0012] According to an aspect of the present invention there is provided a reverse circulation drill bit comprising: an elongate hollow body; a cutting face; a central opening in the cutting face for receiving a cut sample; a generally cylindrically shaped tube located within a hollow portion of the body and extending substantially co-axially with the body so as to define a gap between the tube and the inside wall of the hollow body; an annular entrance extending inwardly from the gap inside of the tube so as to direct fluid travelling through the gap towards the cutting face into the inside of the tube in a direction away from the cutting face.

[0013] Also according to the present invention there is provided a down hole hammer comprising the drill bit defined above.

[0014] In an embodiment all of the fluid entering the gap between the tube and the inside wall of the hollow body is directed through the annular entrance.

[0015] In an embodiment a portion of the fluid is directed past an anvil portion of the body to radially extending splines of the hollow body. In an embodiment fluid is directed to the splines during an impact stroke of a piston. In an embodiment the fluid is directed to the splines when the piston is at a top of cycle position.

[0016] In an embodiment the anvil portion is an annular end face of the hollow body.

[0017] In an embodiment the gap receives an oscillating pressure fluid flow. In an embodiment the fluid is directed into the gap from an annular space between the tube and a casing of a drill rod. In an embodiment the fluid is in the form of air. In an embodiment the fluid flow path between the drill string and the gap is broken during a portion of the piston cycle.

[0018] In an embodiment the gap receives a fluid flow as an exhaust from a piston.

[0019] In an embodiment the body comprises a head on which the cutting face is disposed. In an embodiment the head is removable from the remainder of the body.

[0020] In an embodiment the cutting face comprises radially extending open channels.

[0021] In an embodiment the opening comprises a bevelled portion.

[0022] In an embodiment the cutting face comprises the bevelled portion of the opening.

[0023] In an embodiment the cutting face comprises cutting buttons.

[0024] In an embodiment the head comprises generally radially extending enclosed channels that extend from the opening to an outer opening in the circumferential surface of the head. In an embodiment the channels extend somewhat in an axial direction towards the cutting face as they extend radially.

Brief Description of the Drawings

[0025] In order to provide a better understanding, embodiments of the present invention will be described, by way of example only, with reference to the accompanying drawings, in which:

[0026] Figure 1A is a schematic cross-sectional elevation of a hammer drill rod in a 'blow down' configuration when the bit is extended due to the hammer drill rod being lifted from the bottom of the drill hole;

[0027] Figure 1B is a schematic cross-sectional elevation of the hammer drill rod of Figure 1A in a configuration when the bit is sitting on the bottom of the drill hole and a piston is at a top of travel position;

[0028] Figure 1C is a schematic cross-sectional elevation of the hammer drill rod of Figure 1A in a configuration when the bit is sitting on the bottom of the drill hole and a piston is at a bottom of travel position;

[0029] Figure 2A is a side elevation of a drill bit according to an embodiment of the present invention;

[0030] Figure 2B is a cross-sectional view of the section A-A of Figure 2A;

[0031] Figure 3A is a side elevation of a drill bit according to another embodiment of the present invention;

[0032] Figure 3B is a cross-sectional view of the section B-B of Figure 3A;

[0033] Figure 4A is a side elevation of the drill bit according to a further embodiment of the present invention;

[0034] Figure 4B is a cross-sectional view of the section C-C of Figure 4A;

[0035] Figure 5A is a side elevation of a drill bit according to a further embodiment of the present invention;

[0036] Figure 5B is a cross-sectional view of the section D-D of Figure 5A;

[0037] Figure 6 is a side elevation of another embodiment of the present invention;

[0038] Figure 7 is a side elevation of another embodiment of the present invention;

[0039] Figure 8 is a side elevation of another embodiment of the present invention;

[0040] Figure 9 is a perspective view of the drill bit of Figure 6;

[0041] Figure 10 is a perspective view of an alternative drill bit; and

[0042] Figure 11 is a perspective view of a head of the drill bit of Figure 8.

Detailed Description of Embodiments of the Invention

[0043] Referring to Figure 1A, there is shown a down hole hammer 100, for connection to a drill string (not shown) via a top sub 110. The hammer 100 comprises a drill bit 10 a casing 104, a drive sub 102 for coupling the drill bit 10 to the casing 104. The drill bit 10 and drive sub 102 have complimentary longitudinal splines 108 that allow reciprocal axial movement of the drill bit 10 and also transfer axial rotation of the casing 104 to the drill bit 10. The hammer 100 further comprises a centre tube 32 concentric with the casing 104 that is partially inserted into an open end of the drill bit 10 as described further below. The tube 32 provides a passage 40 for drilled samples to be fed to the surface via the drill string. The hammer 100 also comprises a piston 106 and a fluid control apparatus 112 that receives pressurised fluid from the drill string via the top sub 110. The fluid control apparatus 112 is for actuating the piston 106 so as to impact on an anvil portion 120 of the drill bit 10 in a reciprocating manner. The fluid control apparatus 112 also provides fluid flowto lubricate the splines 108. The fluid control apparatus 112 also provides pressurised fluid flow to a gap 38 (shown in Figure 2B) between the tube 32 and a shank 12 of the drill bit 10 as will be described further below.

[0044] Referring to figures 2A and 2B, there is shown the drill bit 10 comprising an elongate body in the form of a shank 12 and a head 14. The body 12 is configured to receive a percussive force from the piston 106 on the anvil portion 120, which comprises an annular end face of the hollow body.

[0045] The drill head 14 comprises a cutting face 16 for engagement with rock, so as to cut the rock. The drill head 14 cuts into the rock by the application of an axial rotational force applied to the drill bit 10 and a percussive force received through the anvil portion 120 in which the cutting face 16 (or elements thereof) impact the rock thereby cutting/chipping it away as the drill bit 10 advances, thereby drilling into the rock.

[0046] The body 12 is generally of cylindrical shape with radially extending splines 108 (examples of spline patterns are shown in Figures 9 and 10) and a retaining flange 130 at the anvil portion 120. The body 12 has an inner surface 30 defining a hollow cavity within the body 12.

[0047] The head 14 comprises a central opening 18 that opens the cutting face 16 to the cavity within the body 12. A portion of the cutting face 16 may be conically shaped 20 to provide a bevelled shape to the opening 18. The head 14 has a peripheral circumference 22. Adjacent the peripheral circumference 22 may be a conically shaped portion 26 of the cutting face 16. The cutting face 16 also comprises a generally flat portion 24 that sits proud of the bevelled portions 20 and 26.

[0048] Received within the hollow cavity of the body 12 is an end portion of the co-axially extending tube 32. A gap 38 is provided between the outside surface of the tube 32 and the inner surface 30 of the body 12. In an embodiment the inner surface 30 increases in radius part way along the length of the body 12. In an embodiment the tube 32 has an end section 34 which comprises a conically flared end portion 36 that terminates in a circular lip 70. The inner surface 30 extends into the head 14 and transitions to the opening 18 by a curved surface 72 or port hole (in Figure 1A) so as to provide an annular entrance 74 to the inside of the tube 32. The circular lip 70 is positioned substantially at the centre point of the curve of the surface 72 such that fluid travelling through the gap 38 towards the head 14 encounters the curve 72 and is directed through the annular entrance 74 into the tube 32 in a direction away from the head 14.

[0049] An end section 34, including the flared portion 36, may be a trumpet portion that has a slip joint to allow reciprocation of the end section 34 with respect to the tube 32 under the impact of the piston 106.

[0050] In operation fluid is received at the top sub 110. When the piston 106 is at the top of the cycle, as shown in Figure 1B, a bottom sleeve port of the fluid control apparatus 112 is open to deliver fluid to the gap 38. All of the fluid entering the gap 38 is directed through the annular entrance 74 into the tube 32.

[0051] By virtue of a Venturi effect/Coanda effect and Bernoulli's principle, fluid flow from the opening 18 into the channel 40 is magnified and a pressure differential at the opening 18 causes cuttings to be sucked into the opening 18 and thus into the channel 40, where they can then be delivered to the surface through the drill string. In an embodiment due to the flared shape of the end portion 36 the diameter of the inside of the tube 32 decreases away from the lip 70 / cutting face 16.

[0052] In an embodiment a top port of the fluid control apparatus 112 is open to a relief in the piston 106, which has ports to allow air to fill a chamber 140 so as to create movement of the piston 106 in the casing 104 towards the drill bit 10. At the end of the stroke the piston 106 will strike the anvil portion 120 and be in the position shown in Figure 1C. During travel to this position the bottom port is blocked and all fluid supply is directed into the chamber 140 to maximise the striking force of the piston 106.

[0053] In Figure 1C the bottom port is blocked. Just before it strikes the anvil portion 120 the chamber is opened to communicate with a gap between the piston 106 and the tube 32 to exhaust the pressurised fluid through this gap and then into gap 38, which in turn is fed into the inside 40 of tube 32.

[0054] In an embodiment a portion of the fluid is directed past anvil portion 120 of the body to radially extending splines 108 of the hollow body 12. In an embodiment fluid is directed to the splines 108 during an impact stroke of the piston due to pressure forcing fluid though a port in the outer radial periphery of the body 12. In an embodiment the fluid is also directed to the splines 108 when the piston 106 is at a top of cycle position. This allows the splines 108 to be lubricated. Fluid from the splines 108 is exhausted though radial ports in the drive sub 102 that open adjacent to the head 14.

[0055] In an embodiment the gap 38 receives an oscillating pressure fluid flow. In an embodiment the fluid is directed into the gap 38 from an annular space between the tube 32 and the casing 104 of the drill rod. In an embodiment the fluid is the form of air. In an embodiment the air flow is received during a portion of the piston cycle.

[0056] Referring to Figures 3A, 3B and 10, in this embodiment the opening 18 is axially deeper than in the previous embodiment. Extending radially from the opening are a plurality of channels 60 that open at different positions on the peripheral circumference 22. This embodiment may be advantageous when exhaust fluid from the hammer system is directed towards the drill head 14 as it can capture cuttings that may otherwise tend to be forced radially into the borehole.

[0057] Referring back to get to Figure 2B, in this embodiment the drill head 14 is removably attachable to the body 12 by threaded engagement 50. The head 14 is shown removed from the body in Figure 11. This embodiment allows for easier replacement of the head 14, which may have its cutting surfaces worn, without necessarily replacing the remainder of the drill bit 10, specifically the body 12. Furthermore, where the embodiment of the head 14 shown in Figure 3B is used, replacement of the head 14 can be readily accomplished. It is also noted that the extension 34 of the tube 32 into the head 14 is considerably greater in Figure 2B than in Figure 3B. Where the head 14 is replaced this can be accommodated by using a shorter trumpet portion 34 of the tube 32.

[0058] Referring to Figures 4A and 4B. This embodiment is substantially the same as that in Figures 2A and 2B, with the exception being that the head 14 and body 12 are integrally formed. That is, they are made of one piece of material 52. Likewise Figures 5A and 5B are substantially the same as the embodiment of Figures 3A and 3B except that again the head 14 and the body 12 are integrally formed.

[0059] Referring to Figures 6 and 9, the cutting face 16 typically comprises a plurality of hardened buttons 80. The arrangement of buttons 80 often depends on the type of ground being drilled. The arrangement of buttons shown in Figure 6 is merely an example. Other typical arrangements are shown in Figures 7, and 8 and 11, respectively. The arrangement of buttons 80 may be arranged to feed rock cuttings towards the opening 18. The specific arrangement of buttons 80 is not intended to be limiting on the present invention.

[0060] Additionally the cutting face may have open channels 82 radially extending from the opening 18 to the bevelled surface 26. Again the form of these channels may vary, such as the three radially extending channels in Figures 6 and 7, as opposed to the two radially extending channels 82 in Figure 8. The channels allow debris cut by the buttons to be swept into the channel 82 and then to be sucked into the opening 18.

[0061] Further axially extending channels 84 may be positioned around the peripheral circumference 22. Again the arrangement of these axial channels is not intended to be limiting on the present invention, with there being different arrangements of these channels 84 in Figures 6, 7 and 8. These channels 84 allow fluid from the splines 108 to travel to the cutting face 16 or channels 60 where it will be sucked into the inside 40 of tube 32 along with any samples it collects.

[0062] When drilling is finished the drill string is raised and drill bit 10 will drop to the position shown in Figure 1A. In this position, the piston 106 contacts the anvil portion 120 and fluid flow constantly feeds the gap 38.

[0063] The present invention provides advantages over a conventional RC hammer drill because the opening allows larger sized cored drill cuttings to be extracted. Fluid flow through the gap 38 may be pulsed which may provide advantages in de-agglomerating suspected samples or maintaining suspension of the samples in the fluid travelling up the inside 40 of tube 32. Fluid pressure exhausting the hammer mechanism may be drawn around the head 14 by suction in order to capture cuttings.

[0064] The present invention provides advantages of a traditional air core drill in the form of superior sampling but is also able to be used on rock and/or consolidated ground rather than on unconsolidated ground.

[0065] Modifications may be made to the present invention within the context of that described and shown in the drawings. Such modifications are intended to form part of the invention described in this specification.

[0066] One modification contemplated is to allow some of the fluid to be split off away from the cutting face 16 and directed to the centre tube 32 so as to reduce the volume of air reaching the curved surface 72 or port hole.

Claims (19)

Claims

1. A reverse circulation drill bit comprising: an elongate hollow body; a cutting face for drilling at least in part by percussive forces; a central opening in the cutting face for receiving a cut sample; a generally cylindrically shaped tube located within a hollow portion of the body and extending substantially co-axially with the body so as to define a gap between the tube and the inside wall of the hollow body; an annular entrance extending inwardly from the gap inside of the tube so as to direct fluid travelling through the gap towards the cutting face into the inside of the tube in a direction away from the cutting face; wherein all of the fluid entering the gap between the tube and the inside wall of the hollow body is directed through the annular entrance.

2. A drill bit according to claim 1, wherein a portion of the fluid is directed past an anvil portion of the body to radially extending splines of the hollow body.

3. A drill bit according to claim 2, wherein fluid is directed to the splines during an impact stroke of a piston.

4. A drill bit according to claim 2, wherein the fluid is directed to the splines when the piston is at a top of cycle position.

5. A drill bit according to claim 2, wherein the anvil portion is an annular end face of the hollow body.

6. A drill bit according to any one of claims 1 to 5, wherein the gap receives an oscillating pressure fluid flow.

7. A drill bit according to any one of claims 1 to 6, wherein the fluid is directed into the gap from an annular space between the tube and a casing of a drill rod.

8. A drill bit according to any one of claims 1 to 7, wherein the fluid is air.

9. A drill bit according to any one of claims 1 to 8, wherein the fluid flow path between the drill string and the gap is broken during a portion of the piston cycle.

10. A drill bit according to any one of claims 1 to 9, wherein the gap receives a fluid flow as an exhaust from a piston.

11. A drill bit according to any one of claims 1 to 10, wherein the body comprises a head on which the cutting face is disposed.

12. A drill bit according to claim 11, wherein the head is removable from the remainder of the body.

13. A drill bit according to any one of claims 1 to 12, wherein the cutting face comprises radially extending open channels.

14. A drill bit according to any one of claims 1 to 13, wherein the opening comprises a bevelled portion.

15. A drill bit according to claim 14, wherein the cutting face comprises the bevelled portion of the opening.

16. A drill bit according to any one of claims 1 to 15, wherein the cutting face comprises cutting buttons.

17. A drill bit according to any one of claims 1 to 16, wherein the head comprises generally radially extending enclosed channels that extend from the opening to an outer opening in the circumferential surface of the head.

18. A drill bit according to claim 17, wherein the channels extend somewhat in an axial direction towards the cutting face as they extend radially.

19. A down hole hammer comprising the drill bit of any one of claims 1 to 18.