AU2002311319B2

AU2002311319B2 - Reverse Circulation Downhole Hammer

Info

Publication number: AU2002311319B2
Application number: AU2002311319A
Authority: AU
Inventors: Ian Graeme Rear
Original assignee: Sandvik Mining and Construction Australia Production Supply Pty Ltd
Current assignee: Sandvik Mining and Construction Australia Production Supply Pty Ltd
Priority date: 2001-09-06
Filing date: 2002-11-29
Publication date: 2008-04-10
Anticipated expiration: 2022-11-29

Description

29, NOV. 2002 16:51 WRAY AND ASSOCIATES NO. 734 P. P/00)011 28/5191 Regulation 3.2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Name of Applicant Actual Inventor Address for service is: ]an Graeme Rear Ian Graeme Rear WRAY ASSOCIATES Level 4, The Quadrant I William Street Perth, WA 6000 Attorney code: WR Invention Title: *Reverse Circulation Downhole Hammer Details of Associated Provisional Application No: PR7539 filed on 6 September 2001 The following statement is a full desription of this invention, including the best method of performing it known to me:- 29-NOV-2002 16:51 WRAY AND ASSOCIATES NO. 734 P. 6 -2- "Reverse Circulation Downhole Hammer" Field of the Invention This invention relates to a reverse circulation hammer.

Background Art Reverse circulation hammers are commonly used in downhole drilling especially in hard rock drilling. A difficultly with such hammers relates to the circumstance that the flow of exhaust air which carries cuttings from the bore hole can be retarded which results in the grinding of rock chips which are generated by the action of the drill bit. This is not only inefficient but can also be undesirable since in analysing the results of a drilling operation geologists generally tend to prefer large chip samples.

In addition when drilling in soft clay formations there is a tendency for the return passageways of the drill bit to become blocked when inactive and particularly as the hammer is being lowered into the bore hole. The fluid pressure which is generated within the bore hole on activation of the hammer can often be insufficient to clear the return passageways.

In addition in mud formations there can be a tendency for mud and clay to enter into the exhaust passageways within the drill bit support when the hammer is unpressurised which will be the case can occur when it becomes necessary to introduce additional lengths of drill rod into the drill string. Such material can block the exhaust passageways which enable the escape of exhaust fluid from the piston chamber and as a result, when the piston chamber is pressurised there is no exhaust from the chamber which prevents the piston from commencing its reciprocation within the piston chamber.

In addition, as a result of normal wear and tear within the hammer there can be an increased degree of leakage within the piston chamber resulting in the development of a high pressure condition between the piston and the upper end 29.NOV.2002 16:51 29. NV. 2Q2 1:51 RAY AND ASSOCIATES NO. 734 P. 7/ -3of the chamber (particularly under "blow down" conditions) which can result in a difficulty in initiating the reciprocation of the piston when the hammer is to be reactivated.

Disclosure of the Invention Accordingly, the invention resides in a reverse circulation downhole hammer comprising a casing supporting a top sub at one end and a drill bit support at the other end, a chamber defined within the casing between the ends thereof, an inner tube supported in the chamber from the top sub to be coaxial within the casing and adapted to communicate with an exhaust passage provided in a drill bit to be supported by the drill bit support, a piston slidably supported in the chamber over the inner tube for reciprocation between the top sub and the drill bit support porting means adapted to deliver pressurised fluid from the top sub to the chamber to cause the reciprocation of the piston with~in the chamber, exhaust passagesways provided in the drill bit support adapted to exhaust fluid from the chamber to the drill bit, fluid ports provided in the inner tube to provide fluid flow from the chamber to the interior of the tube during reciprocation of the piston within the chamber to induce a fluid flow into the inner tube from the drill bit.

According to a preferred feature of the invention the fluid ports are located in the inner tube towards the other end of the casing.

According to a further preferred feature of the invention the fluid ports are inclined Inwardly with respect to the central axis of the inner tube in the direction of the other end of the casing.

According to a preferred feature of the invention, the fluid ports are spaced around the inner tube. According to one embodiment the fluid ports are spaced at equidistant intervals around the tube.

According to a preferred feature of the inventon the fluid ports provide said fluid flow to the interior of the tube substantially constantly throughout the 29-NOV-2002 16:51 WRAY AND ASSOCIATES NO. 734 P, 8 -4reciprocation of the piston. According to an alternative preferred feature of the invention the fluid ports provide said fluid flow to the interior of the tube when the piston is in the vicinity of its end positions within the chamber.

According to a preferred feature of the invention, the drill bit support is adapted to enable the drill bit to be moveable outwardly from the casing to a "blowdown" position at which the piston is retained in engagement with the drill bit support, wherein when the hammer is at that condition the fluid ports provide said fluid flow to the interior of the tube.

The invention will be more fully understood in the light of the following description of one specific embodiment.

Brief Description of the Drawings The description is made with reference to the accompanying drawings of which: Figure 1 is a sectional side elevation of a downhole hammer according to the embodiment showing the piston in its impact position; Figure 2 is a sectional side elevation of the hammer according to the embodiment showing the piston in the raised position; Figure 3 is a sectional side elevation of a hammer according to the first embodiment showing the piston in the "blowdown" position; Figure 4 is a side elevation of an inner tube according to the first embodiment; Figure 5 is a cross section of the inner tube alone line 5-5 of figure 4.

Detailed Description of Specific Embodiment The embodiment as shown in the accompanying drawings comprises a downhole reverse circulation hammer which is used to be utilised in the formation of bore holes in the ground. The hammer comprises a casing 11 which 29. NOV. 2602 16:51 WA N SOITSN.74

P

WRAY AND ASSOCIATES NO. 734 P. 9 supports a top sub 13 at one end and a drill bit support 15 at the other end. The drill bit support retains a drill bit 17 by means of a retaining ring 19 provided in the drill bit support 15 which is engagable with an annular splined collar 21 provided at the inner end of the drill bit such that the drill bit is capable of limited slidable movement within the drill bit support.

The interior of the casing I11 provides a piston chamber 23 between the top sub 13 and the dnill bit support 15. In addition, the top sub 13 supports an inner tube which is coaxial with the casing 11 and extends from the top sub into the drill bit support such that its outermost end is slidably receivable in an exhaust passage provided in the drill bit 17 which is formed with exhaust ports 29 in its outer axial face which extend between the outer axial face of the drill bit 17 and the exhaust passageway 27. The engagement of the inner tube 25 within the drill bit 17 ensures that there is constant communication provided between the interior of the inner tube 25 and the exhaust ports 29 when the piston is in its operative position as shown at Figures 1 and 2 and in the "blow down" position as shown at Figure 3.

The piston chamber 23 accommodates a piston 30 which is slidably received within the piston chamber 23 and over the inner tube 25 such that the piston is capable of reciprocation between an Impact position as shown at Figure 1 at which it is in engagement with the inner end 39 of the drill bit 17 and a raised position as shown at Figure 2 at which is in closely spaced relation With the top sub. The internal bore of the piston is greater than the external diameter of the inner tube for most of the length of the inner tube to define an annular passageway thurebetween. The portion of the inner tube adjacent the top sub has a diameter corresponding to the internal diameter of the piston in order that the piston sealing engages the inner tube when in its raised positon as shown at Figure 2. The piston is formed with set of annular ribs 33 at spaced intervals along its length.

In addition the interior of the casing is associated with an inner sleeve 31 which extends from the top sub 13 to form the internal face of the casing in the region 29. NOV 2002 16:52 WRAY AND ASSOCIATES NO. 734 P. -6proximate the top sub and to define a plenum between the external face of the sleeve and the opposed internal face of the casing which is in communication with the top sub. The casing is provided with two sets of inlet ports 35 and 37 which open into the piston chamber to provide communication between the plenum and the piston chamber at spaced axial positions along the length of the sleeve. The ribs 33 of the piston are slidably and sealingly engaged with the internal face of the casing and sleeve to define a first sub-space A between the drill bit support and the adjacent end of the piston and a second space B between the top-sub and the adjacent end of the piston.

In use the hammer is connected to a dual walled drill rod whereby the inner tube is connected to a central return passageway provided within the drill rod and the pressurised fluid is delivered to the top sub of the hammer through the outer annulus provided in the drill rod. The pressurised fluid is delivered from the drill rod into the top sub and then to the plenum defined between the casing 11 and the sleeve 31.

With reciprocation of the piston within the piston chamber the ribs cooperate with the inlet ports 35 and 37 to sequentially permit the admission of fluid into the first space A when the piston is in the impact position as shown at Figure 1 to cause the piston to move to its raised position and then to the second space B when the piston is at its raised position as shown at Figure 2 to cause the piston to be driven to the impact position as shown at Figure 1. As a result reciprocation of the piston within the piston chamber is effected through the controlled delivery of pressurised fluid into the piston chamber through the ports 35 and 37 which delivery is controlled by virtue of the nribs 33 provided on the piston 30. The fluid in each space is exhausted from each space as that space is contracting where the exhausted fluid flows from the piston chamber through fluid exhaust passageways defined between the drill bit and the drill bit support. In the case of the second space the exhausted fluid initially passes from the second space B through the annular passageway defined between the inner tube and the bore of the piston. The fluid which is exhausted from the hammer is delivered into the bore hole through the splined passageway provided between the drill bit support ANOV-2002 16:52 WRAY AND ASSOCIATES 29.NOV 202 1:52 RA AN ASOCITESNO. 734 P. 11 -7and the drill bit 17 to return to the surface through the exhaust ports 29 provided on the outer face of the drill bit, the exhaust passage 27 and the inner tube In addition the hammer according to the embodiment is provided with a set of fluid ports 40 which are provided around the inner tube 25 at a position located proximate its free end. The ports 40 provide communication between the annular space defined between the inner tube 25 and the bore of the piston. In order to provide the ports 40 without adversely affecting the strength of the inner tube, the outer wall of the inner tube 25 is provided with an enlarged portion 41 through which each fluid port passes. The fluid ports 40 are spaced at equidistant intervals around the inner tube and are inclined inwardly With respect to the central axis of the inner tube in the direction of the top sub. As a result the ports provide a restricted flow of exhaust fluid from the first and second space into the interior of the inner tube 25 during reciprocation of the piston 30 within the piston chamber 23. As a result there is a constant delivery (although restricted) of pressuilsed fluid into the interior of the inner tube 25 which is in a direction corresponding to the flow of exhaust fluid and cuttings Within the inner tube When At is desired that the hammer be deactivated the drill string is raised from the bore hole which causes the drill bit 17 to slide outwardly within the drill bit support such that the annular collar 21 becomes engaged with the retaining ring 19, and the hammer adopts the "blow down" position as shown at Figure 3. At this position the piston 30 is retained in its lower most position within the casing and the second space B between the piston and the top sub is pressurised to a greater extent than the first space A between the piston and the drill bit support in that pressurised fluid is delivered directly into the space B to be exhausted through the annular space provided between the inner tube 25 and the internal bore of the piston 30. When in this mode pressurised fluid is caused to be introduced in to the inner tube 25 through the fluid ports 40 to maintain a flow of fluid along the inner tube 25 away from the drill bit 17.

29-NOV-202 16:52 WRAY AND ASSOCIATES NO. 734 P. 12 -8- It has been found that in using conventional down hole reverse circulation hammers which do not incorporate fluid ports 40 of the form described above several difficulties can arise. One such difficulty relates to the regrinding of cuttings generated by the direction of the drill bit in the bore hole as a result of an inadequate flow of cuttings on the space between the cutting face of the drill bit and the bore hole. This is not only inefficient but also disadvantageous since in analysing the results of a drilling program geologists generally prefer larger rock chips to be recovered from the drilling action. In addition, in clay formations there is a tendency that the exhaust ports 29 in the drill bit can become blocked on introduction of the drill bit into the ground and can be difficult to unblock. A further difficulty that arises is that in mud formations there is a tendency for mud and clay to enter the exhaust passageways provided between the drill bit and drill bit support when pressurised fluid is not being delivered to the drill bit (which can occur during rod changes) which will cause the exhaust passageways to become blocked and prevent the reactivation of the piston. In addition once a hammer has have been subjected to some wear, there can be a tendency for a leakage of pressurised fluid into the second space B provided between the piston and the top sub which will cause pressurisation of the second space when the hammer is in the "blow down" mode which can create difficulties when its necessary to reactivate the hammer.

It has been found in testing of a hammer according to the embodiment that the presence of the fluid ports provide a substantially constant fluid flow into the inner tube in the direction away from the drill bit. This tends to produce a low pressure zone in the exhaust passage 27 and exhaust ports 29 of the drill bit.

This negative pressure serves to enhance the flow of exhaust fluid and cuttings from the bore hole which reduces the degree of regrinding of the cuttings generated by the action of the drill bit in the bore hole and result in larger chips being delivered to the surface. In addition the negative pressure that is created serves to reduce the likelihood of blockage of the exhaust ports and exhaust passageway which may otherwise occur in clay or mud formations. Furthermore, it has been found that penetration rates of the drill bit increase slightly under hard rock conditions and appreciably in soft ground conditions. A further advantage 29.NOV.2002 16:53 WRAY AND ASSOCIATES NO. 734 P. 13 -9which has been found is that in mud formations where there is a tendency for mud or clay to enter the exhaust passageways defined in the absence of pressurised fluid being delivered to the hammer, that when the hammer is reactivated by the introduction of pressurised fluid into the hammer the controlled bleed-off of air from the piston chamber through the fluid ports serves to assist in pressurising the second space B between the piston and the top sub to cause the activation of the hammer and promote the dislodgement of clay and mud in the exhaust passageways. Furthermore, in the case of worn hammers it is expected that the bleeding off of pressurised air from the second space B will serve to depressurise the second space B between the piston and the top sub when the piston is in its impact position to minimise the difficulty of reactivating the piston.

Throughout the specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

It should be appreciated that the scope of the present invention need not be limited to the particular scope of the embodiment described above.

Claims

1. A reverse circulation downhole hammer comprising a casing supporting a top sub at one end and a drill bit support at the other end, a chamber defined within the casing between the ends thereof, an inner tube supported in the chamber from the top sub to be coaxial within the casing and adapted to communicate with an exhaust passage provided in a drill bit to be supported by the drill bit support, a piston slidably supported in the chamber over the inner tube for reciprocation between the top sub and the drill bit support, porting means adapted to deliver pressurised fluid from the top sub to the chamber to cause the reciprocation of the piston within the chamber, exhaust passageways provided in the drill bit support adapted to exhaust fluid from the chamber to the drill bit, fluid ports provided in the inner tube to provide fluid flow from the chamber to the interior of the tube during reciprocation of the piston within the chamber to induce a fluid flow into the inner tube from the dril bit.

2. A reverse circulation downhole hammer as claimed at claim I wherein the fluid ports are located in the inner tube towards the other end of the casing.

3. A reverse circulation downhole hammer as ciaimed at claim 1 or 2 wherein the fluid ports are inclined inwardly with respect to the central axis of the inner tube in the direction of the other end of the casing.

4. A reverse circulation downhole hammer as claimed at claim 1 or 2 or 3 wherein the fluid ports are spaced around the inner tube.

5. A reverse circulation downhole hammer as claimed at claim I or 2 or 3 or 4 wherein the fluid ports are spaced at equidistant intervals around the tube.

29-NOV202 16:53 WRAY AND ASSOCIATES NO. 734 P, 11 6. A reverse circulation downhole hammer as claimed at claim 1 or 2 or 3 or 4 or 5 wherein the fluid ports provide said fluid flow into the inner tube substantially constantly throughout the reciprocation of the piston. 7. A reverse circulation downhole hammer as claimed at claim 1 or 2 or 3 or 4 or 5 wherein the fluid ports provide said fluid flow into the inner tube when the piston is in the vicinity of its end positions within the chamber. 8. A reverse circulation downhole hammer as claimed at any one of the preceding claims wherein the drill bit support is adapted to enable the drill bit to be moveable outwardly from the casing to a "blowdown" position at which the piston is retained in engagement with the drill bit support, wherein when the hammer is at that condition the fluid ports provide said fluid flow into the inner tube. 9. A reverse circulation downhole hammer substantially as herein described with reference to the accompanying drawings. Dated this twenty ninth day of November 2002. lan Graeme Rear Applicant Wray Associates Perth, Western Australia Patent Attorneys for the Applicant