AU729944B2

AU729944B2 - Improved fluid operated hammer

Info

Publication number: AU729944B2
Application number: AU28347/97A
Authority: AU
Inventors: Ian Graeme Rear
Original assignee: Individual
Current assignee: Individual
Priority date: 1996-06-28
Filing date: 1997-06-27
Publication date: 2001-02-15
Anticipated expiration: 2017-06-27
Also published as: AU2834797A

Description

P/00/011 28/5/91 Regulation 3.2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT

S.

*5 S

S

S*SS

S..

S. S

S

S. S S

S.

Name of Applicant: Actual Inventor(s): Address for service is: lan Graeme Rear lan Graeme Rear WRAY ASSOCIATES 239 Adelaide Terrace Perth, WA 6000 Attorney code: WR Invention Title: Improved Fluid Operated Hammer Details of Associated Provisional Application No(s): P00733 The following statement is a full description of this invention, including the best method of performing it known to me:- -2- The present invention relates to a fluid operated down hole hammer.

The hammer may take the form in which fluid is exhausted through axial apertures provided in the drill-bit into the bore hole to be retumrned to the surface between the sides of the hammer casing and the sides of the bore hole or alternatively to a reverse circulation hammer in which the fluid is exhausted between the casing and the sides of the drill-bit in order to pass across the cutting face of the drill-bit and retumrned to the surface through axial passageways provided in the drill-bit.

In order to improve drilling efficiencies and speed there has been an increasing trend to increase the operating pressure of the air or fluid which is delivered to the hammer. Other reasons for the increased pressure and volume of air has been for the purposes of ensuring adequate clearance of the bore hole particularly under "blow down" conditions in deep holes or when drilling below the water table when the hammer is retracted from the bottom of the bore hole to allow the drill-bit to move outwardly with respect to the hammer casing to render the hammer inactive. This action also serves the purpose of delivering air or fluid into the borehole in order to clear the hole and/or water within the hole. Under these blow down conditions it is desirable to maximise the volume of the fluid flow into the bore hole in order to the ensure the rapid and complete clearance of any residual cuttings or water in the bore hole. While the pressure of the air which can be delivered to a hammer has been increasing the hammers have been ported to maximise the efficient use of such high pressure air in their hammering action which has involved a reduction in the sizes of the ports in the hammer. This in turn has resulted in a restriction of the volume of air which can be passed through the hammer into the borehole, even under blow down conditions. Therefore while the hammers may be able to drill efficiently and rapidly, difficulties are experienced when it becomes necessary to clear the hole of cuttings and/or water which requires the rapid delivery of a high volume of air into the borehole and the maintenance of such delivery. Therefore it is desirable to provide a hammer which is able to deliver large volumes of air into the bore hole under "blow down" conditions in the shortest period of time and yet which is able to operate efficiently with high pressure air or fluid.

-3- It is an object of this invention to provide a hammer which is able to operate efficiently under high pressure conditions and which is able to deliver a significantly greater volume of air or fluid into the borehole under blowdown conditions.

Accordingly the invention resides in a fluid operated down hole hammer comprising a cylindrical casing having a top-sub at one end and a drill-bit support at the other end, said drill-bit support being adapted to accommodate a drill-bit such that the drillbit is capable of limited axial slidable movement within the casing, said hammer further comprising a central feed tube supported from the top-sub and extending into the casing towards the other end of the casing, said feed tube being closed, a piston slidably supported in the casing for reciprocation therein over the feed tube, a pair of longitudinally spaced first apertures in the wall of the feed tube, ports provided in the piston and extending between the internal wall of the piston and the exterior, the ports being positioned to periodically communicate with one or the other of the first 0 apertures to deliver fluid sequentially to a first space between the one end of the 15 casing and the piston and a second space between the other end of the casing and 9. the piston and to vent the second and first space respectively in order to effect reciprocation when the drill-bit is innermost within the casing, one end portion of the **...piston which is proximate the other end of the casing being of a reduced diameter, a second aperture provided in the wall of the feed tube and positioned towards the 20 one end of the casing to be sealingly engaged by the piston throughout the movement of the piston when the drill-bit is innermost within the casing and to be exposed to admit fluid into the first space when the drill-bit is in its outermost position o9e9999 .in the casing and the piston is adjacent the inner end of the drill-bit, said first space being in communication with the exterior of the drill-bit when the drill-bit is in its outermost position in the casing.

According to a preferred feature of the invention the end portion of the inner wall of the casing proximate the other end is of a reduced diameter wherein said one end portion of the piston and the end portion of the inner wall of the casing are dimensioned to be sealingly interengaged when the piston is adjacent the other end of the casing and when the drill-bit is innermost within the casing. According to a preferred embodiment said end portion of the wall is provided by an annular bush supported by the other end of the casing.

According to a further preferred feature of the invention, said aperture is of enlarged dimensions and said first apertures are of reduced dimensions.

According to a preferred feature of the invention, fluid is exhausted from the first and second spaces into one or more axial passageways provided in the drill-bit.

According to an alternative preferred feature of the invention, the hammer is a reverse circulation hammer and supports a return passageway which extends between the ends of the casing, said feed tube being concentrically received over the return passageway, wherein the fluid exhausted from the first and second spaces passes from the hammer between the casing and the drill-bit or the drill-bit support. According to a preferred feature of the previous feature the piston is .supported from the end portion of the wall when the drill-bit is in its outermost position at which position the piston is spaced from the inner end of the drill-bit.

15 The invention will be more fully understood in the light of the following description of two specific embodiments. The description is made with reference to the accompanying drawings of which: Figure 1 comprises a sectional side elevation of a down hole hammer according to the first embodiment in which the piston is in its impact position; Figure 2 is a corresponding view of the embodiment of Figure 1 with the piston in its raised position; and Figure 3 is a corresponding view of the embodiment of Figures 1 and 2 with the drillbit in the "blow down" position.

The embodiment is directed to a reverse circulation hammer which can be used with high pressure fluid. The hammer comprises a cylindrical casing 11 which supports a top-sub 12 at one end and a drill-bit support or chuck 13 at its other end. The drill-bit support 13 accommodates a drill-bit 14 which is slidably receivable in the other end of the casing but is limited in its axial movement by a bit retaining ring 15 such that the drill-bit is only capable of limited movement within the casing. The inner end of the drill-bit 14 is provided with an anvil 16 which lies innermost within the casing.

The support between the drill-bit and the casing is such that fluid is able to readily flow from within the casing into the borehole and around the sides of the drill-bit in accordance with conventional practice in reverse circulation hammers.

The top-sub 12 supports an inner return tube 17 which extends throughout the length of the casing and is slidably received within a central axial passageway 18 provided in the drill-bit whereby the drill-bit is slidably received over the outer end of the return tube throughout its slidable movement within the drill-bit support. The return tube 17 is intended to be connected to a return passageway provided in the drill string when the hammer is mounted to the drill string. In addition the top-sub supports a feed tube 19 which is concentrically received over the return tube 17 and 15 extends into the casing 11 for a portion of the length of the return tube. The outer S*o end of the feed tube is sealingly engaged with an annular rib 20 provided on the external surface of the retumrn tube 17 which supports a O-ring 21 to effect such sealing engagement.

The interior of the casing slidably accommodates a piston 22 which is sealingly :20 received over the feed tube 19 and is capable of reciprocation within the casing between the top-sub 12 and the drill-bit support 13. In addition the other end of the casing supports an annular seal bearing bush 23 which is received over the inner S" wall of the casing 11 in the region adjacent the other end of the casing and which serves to provide a reduced diameter portion in the inner wall towards the other end of the casing 11.

The end of the piston 22 which is proximate the other end of the casing is formed with a reduced diameter portion 24 which is capable of being received through the seal bearing bush 23. The outer most end of the reduced diameter portion 24 of the piston is formed with an enlarged portion 25 while the innermost end of the seal bearing bush 23 is formed with an annular rib 26 which is of corresponding diameter to the enlarged portion 25 of the reduced diameter portion 24 of the piston such that -6when the enlarged portion 25 is received by the rib 23 they substantially sealingly engage with each other, but on the enlarged portion 25 moving into the seal bearing bush 23 beyond the rib 26 the sealing engagement between the piston and the seal bearing bush 23 ceases to exist. The rib 26 is positioned such that when the drill-bit 14 is in its innermost position within the casing as shown at Figures 1 and 2 the enlarged portion 25 of the piston will be in sealing engagement with the rib 26 of the seal bearing bush 23, when the piston is in face to face engagement with the anvil 16 of the drill-bit 14 as shown at Figure 1.

The axial length of the reduced diameter portion 24 is such that when the drill-bit is in its outer most position ("blow down" position), as shown at Figure 3, the innermost extent of the reduced diameter portion 24 will bear against the innermost end of the seal bearing bush 23 to support the piston when proximate the drill-bit support and as a result the end face is in spaced relation to the face of the anvil 16 of the drill-bit 14.

15 The feed tube 19 is provided with a pair of longitudinally spaced first apertures 27 and 28 while the piston is provided with two sets of ports 29 and 30 which are intended to co-operate with the first apertures 27 and 28 to effect sequential delivery of pressurised fluid from within the feed tube to a first space provided between the other end of the casing 14 and piston and a second space B provided between the 0 20 one end of the casing and the piston. The first apertures 27 and 28 may each comprise one or more apertures angularly spaced around the feed tube 17 and similarly the sets of ports 29 and 30 may each comprise one or more apertures angularly spaced around the piston.

As shown at Figure 1 when the piston is in its impact position which is when the drillbit 14 is in its innermost position within the casing 11 and the piston 22 is in face to face engagement with the anvil 16 of the drill-bit 14 one of the first apertures 27 communicates with one of the set of ports 29 provided in the piston to cause fluid to be introduced into the first space A which is defined between the inner wall of the casing 11, the reduced diameter portion 24, the piston 22 and the seal bearing bush 23. In addition the second space B is in communication with the space defined between the intemrnal bore of the piston 22 and the retum tube 17 through the other -7set of ports 30 provided in the piston whereby on the piston disengaging from the anvil 16 of the drill-bit 14 and moving towards the one end of the casing, the fluid in the second space B will be exhausted through the exterior of the hammer between the external face of the drill-bit 14 and the drill-bit support. The pressurisation of the first space A causes the piston to move towards the one end of the casing until such time as the other first aperture 28 communicates with the other set of ports provided in the piston as shown at Figure 2 which then causes pressurised fluid to be introduced into the second space B through the other set of ports 30. When at this position the first space A is in open communication with the exhaust passageways provided in the hammer between the drill-bit support and the drill-bit.

As a result of the pressurisation of the second space B the piston is driven towards the drill-bit 14 to impact on the anvil 16 of the drill-bit 14.

V The first apertures 27 and 28 are of a reduced dimension and as a result this serves to ensure that despite the circumstance that the fluid being delivered to the hammer 15 is of a high pressure there is a controlled delivery of pressurised fluid into the first and second space A and B respectively and that the operation of the hammer is not adversely affected by the high pressure fluid being delivered to the hammer.

The feed tube 19 is provided with a second aperture 31 which is spaced between the first apertures 27 and the one end of the casing. The second aperture 31 is 20 located such that when the drill-bit 14 is in its innermost position and the piston is being caused to reciprocate within the casing 11 as a result of the sequential delivery of pressurised fluid to the first and second space A and B the second aperture 31 is sealingly closed by the internal bore of the piston 22. On the drill-bit 14 moving to its outermost position in the casing (ie its blow down position) as shown at Figure 3 the piston is moved correspondingly within the casing as a result of pressure differentials to each side thereof until it is engaged with and supported by the innermost end of the seal bearing bush 23. When at this position the second aperture 31 becomes disengaged from the internal bore of the piston 22 to be in open communication with the second space B provided between the one end of the casing and the piston 22. In addition, when at this position the pressurised fluid from the second space B communicates with the space defined between the internal bore -8of the piston 22 and the extemrnal face of the return tube 17 through the other set of ports 30. In addition since the piston 22 is supported by the seal bearing bush 23 such that its out of face to face engagement with the anvil 16 of the drill-bit 14, such pressurised fluid is permitted to escape from the exhaust passageways provided between the drill-bit support and the drill-bit and in to the bore hole around the sides of the drill-bit.

The second aperture is of enlarged dimensions in order to maximise the delivery of fluid into the bore hole when the drill-bit is in its outermost position (ie its "blow down" position) in the casing. The second aperture can be of increased dimensions without detracting from the efficiency of the hammer since it does not play any part in effecting the reciprocation of the piston and therefore the cross sectional area of the aperture can be maximised and may comprise a plurality of circumferentially spaced apertures in order to maximise the flow of pressurised fluid into the bore hole.

A second embodiment of the invention (not shown) comprises a conventional down 15 hole hammer in which the fluid is exhausted from the hammer through axial passageways provided through the drill-bit for retumrn to the surface between the sides of the hammer and the sides of the bore hole. Such a hammer does not require the presence of the retumrn tube 17 of the first embodiment and as a result the free end of the feed tube 19 is closed by a plug or any suitable means. In addition 20 the piston is able to be supported from the anvil 16 of the drill-bit 14 when the drill-bit is in its outermost (ie its "blow down") position rather than be supported from the seal to. bearing bush.

too. It should be appreciated that the scope of the invention need not be limited to the particular scope of either of the embodiments described above.

Claims

1. A fluid operated down hole hammer comprising a cylindrical casing having a top- sub at one end and a drill-bit support at the other end, said drill-bit support being adapted to accommodate a drill-bit such that the drill-bit is capable of limited axial slidable movement within the casing, said hammer further comprising a central feed tube supported from the top-sub and extending into the casing towards the other end of the casing, said feed tube being closed, a piston slidably supported in the casing for reciprocation therein over the feed tube, a pair of longitudinally spaced first apertures in the wall of the feed tube, ports provided in the piston and extending between the internal wall of the piston and the exterior, the ports being positioned to periodically communicate with one or the other of the first apertures deliver fluid sequentially to a first space between the one end of the casing and the piston and a second space between the other end of the casing and the piston and to vent the second and first space respectively in order to effect 15 reciprocation when the drill-bit is innermost within the casing, one end portion of the piston which is proximate the other end of the casing being of a reduced diameter, a second aperture provided in the wall of the feed tube and positioned towards the one end of the casing to be sealingly engaged by the piston throughout the movement of the piston when the drill-bit is innermost within the 20 casing and to be exposed to admit fluid into the first space when the drill-bit is in its outermost position in the casing and the piston is adjacent the inner end of the drill-bit, said first space being in communication with the exterior of the drill-bit when the drill-bit is in its outermost position in the casing.

2. A fluid operated down hole hammer as claimed at claim 1 wherein the end portion of the inner wall of the casing proximate the other end is of a reduced diameter wherein said one end portion of the piston and the end portion of the inner wall of the casing are dimensioned to be sealingly interengaged when the piston is adjacent the other end of the casing and when the drill-bit is innermost within the casing

3. A fluid operated down hole hammer as claimed at claim 2 wherein said end portion of the inner wall of the casing is provided by an annular bush supported by the other end of the casing.

4. A fluid operated down hole hammer as claimed at claim 1 or 2 or 3 wherein said second aperture is of enlarged dimensions and said first apertures are of reduced dimensions.

A fluid operated down hole hammer as claimed at claim 1 or 2 or 3 or 4 wherein fluid is exhausted from the first and second spaces into one or more axial passageways provided in the drill-bit.

6. A fluid operated down hole hammer as claimed at any one of the preceding claims wherein the hammer is a reverse circulation hammer and supports a retum passageway which extends between the ends of the casing, said feed tube *being concentrically received over the retumrn passageway, wherein the fluid exhausted from the first and second spaces passes from the hammer between the casing and the drill-bit or the drill-bit support.

7. A fluid operated down hole hammer as claimed at claim 6 as dependant on claim 2 wherein the piston is supported from the end portion of the inner wall of the casing when the drill-bit is in its outermost position, at which position the piston is spaced from the inner end of the drill-bit. 20

8. A fluid operated down hole hammer substantially as herein described Dated this TWENTY-SEVENTH day of JUNE 1997. IAN GRAEME REAR Applicant Wray Associates Perth, Westemrn Australia Patent Attorneys for the Applicant