Field of the invention

The present invention relates to fluid RC drilling and dual walled drill rods for fluid RC drilling that can then be converted to drill rods for wireline core sample drilling and back again.

Background to the invention

In mineral and/or sub terrain exploration, typically one and/or two drilling processes are used to get to the zone of interest. One of the two processes is reverse circulation (RC) drilling (with compressed air) that allows chip samples to be obtained from the formation which can be brought back to surface for analysis while drilling the borehole. The second of the two processes is core drilling that allows a core sample to be obtained of the formation that provides accurate information of the formation. Generally, core drilling is undertaken when the zone of interest in the formation has been reached using the RC drilling process, although in some instances the geologist may specify to just use core drilling from surface. It is appreciated that core drilling is slower by the fact the process must stop in order to retrieve the core sample.

With traditional RC drilling, the total apparatus includes a large heavy drill rig, air compressors and a drillstring that is assembled from a plurality of heavy, double walled drill rods, and any other components required to carry out the RC drilling process, such as hammers, bits and the like. For core drilling, this is carried out with a significantly smaller drill rig, because there is no requirement for compressors and the drillstring is assembled from lightweight drill rods and other components such as a wireline retrievable core barrel, coring bits etc., and other components that are lowered into the bore hole. This process occurs after the RC drillstring has been removed and then operated to carry out coring.

RC drilling is a process that typically requires significant power input in order to drive the hammer downhole in the form of low speed/high torque drives. As such in prior art systems, pneumatic RC drilling is undertaken where large compressors are used to drive the pneumatic hammer. The use of such large compressors and therefore pneumatic hammers, creates significant pressures, which then requires drill rods that can withstand such pressures. Consequently, the drill rods are made of heavy walled steel tube that then makes the drill rods heavy which then requires an equally strong and robust drill rig frame, that is also heavy to hoist and lower the drillstring whether uphole or downhole. These additional weights consequently require more power to drive the entire system leading to increased power inputs. For example, a conventional 3.5" RC rod used for conventional air RC drilling systems weighs approx. 67Kgs per 3 metre length. So, for a 250m drillstring, the drill rods alone weigh approximately 5600g. As a result, the drillstring requires a heavy-duty drill rig to operate the drillstring. The heavy-duty drill rig may be truck or track mounted with the addition of the necessary compressors to drive the larger system.

In comparison, core sample drilling requires an accurate analysis of the formation where the core sample must be kept intact. Thus, the use of compressors and high-powered hammers etc., used in RC drilling is replaced with a high speed/low torque drive. As non-compressible drilling fluids are used, the drill rods used can be considerably lighter typically around 47kg per 3meter length, consequently the drillstring is lighter (3920g for a 250m drillstring) and therefore the need for a heavy-duty drill rig as used in RC drilling is not necessary.

Summary of invention

It is an object of the invention to provide a drill rod and/or its method of assembly for use in fluid RC drilling.

In one aspect the present invention may be said to comprise a drill rod for assembly with other drill rods to form a drillstring used for fluid reverse circulation drilling comprising: an outer drill rod comprising a lightweight drill rod used in core drilling with a bore, an inner drill rod comprising a bore, a first coupling member removably coupled to one end of the inner drill rod, a second coupling member removably coupled to a second end of the inner drill rod, wherein the first and second coupling members centre the inner drill rod within the outer drill rod.

Optionally the core drilling is wireline core drilling and/or the lightweight drill rods are wireline core sampling drill rods.

Optionally the first coupling member provides a first removable coupling and the second coupling member provides a second removable coupling to enable a corresponding first and/or second coupling member in another dual walled drill rod to be coupled.

Optionally a third member is provided that is removably coupled to the outer drill rod to retain either the first and/or second coupling member within the outer drill rod.

Optionally the third member is a coupling member that comprises the second coupling member as an inner coupling member and also comprises an outer coupling member.

Optionally the second coupling member forms part of an outer coupling member that comprises the second coupling member as an inner coupling member and also comprises an outer coupling.

Optionally the second coupling member is further removably coupled to a first end of the outer drill rod, wherein the second coupling member comprises: a first inner coupling that removably couples the second coupling member to the second end of the inner drill rod, and a first outer coupling that removably couples the second coupling member the first end of the outer drill rod.

Optionally the second coupling member also couples the outer drill rod to another outer drill rod in a drill string.

Optionally the first coupling member is a box the second coupling member is a pin and the third member is a third coupling member.

Optionally the third coupling member also couples the outer drill rod to another outer drill rod in a drill string.

Optionally the third coupling member forms part of the outer drill rod.

Optionally the third coupling member has an outside diameter larger than the outer drill rod.

Optionally the box or pin is provided with a seal. Optionally the inner drill rod assembly provides fluid porting around the outside of the inner rod and inner rod third coupling members.

In another aspect the present invention may be said to comprise a method of assembling a dual walled drill rod for subsequent assembly with other drill rods to form a drill string used for fluid reverse circulation drilling, the method comprising in any suitable order: coupling a first coupling member to a first end of an inner drill rod, coupling a second coupling member to a second end of the inner drill rod, placing the coupled inner drill rod assembly into an outer drill rod.

Optionally the method further comprises coupling a third member to a first end of the outer drill rod.

Optionally the method further comprises coupling the third member to an end of a corresponding dual walled drill rod.

Optionally the dual walled drill rod is any one of the paragraphs above.

Optionally them method comprises coupling the dual walled drill rod of any paragraph above to another dual walled drill rod of any paragraph above.

In another aspect the present invention may be said to comprise a method of disassembling a dual walled drill rod, being a drill rod of any paragraph above so that an outer drill rod of the dual walled drill rod can be assembled with other drill rods to form a drillstring used for core sampling, the method comprising: removing the third retention member from the outer drill rod, removing the inner drill rod/retention member assembly from the outer drill rod, assembling the outer drill rod with other such drill rods for core sampling.

In another aspect the present invention may be said to consist in a method of disassembling a dual walled drill rod, being a drill rod of any paragraph above so that an outer drill rod of the dual walled drill rod can be assembled with other drill rods to form a drillstring used for core sampling, the method comprising: removing the inner drill rod/retention member assembly from the outer drill rod, assembling the outer drill rod with other such drill rods for core sampling. In another aspect the present invention may be said to comprise a method of RC drilling and core sampling comprising: assembling a first drillstring with dual walled drill rods according to any paragraph above and/or using the assembly method of any paragraph above, operating the first drillstring using a lightweight drill rig to perform fluid RC drilling, resulting in a borehole, upon completion of RC drilling, extracting the drill string from the borehole, disassembling the drill rods of the first drillstring according to above, assembling a second drillstring with the outer drill rods, along with core sampling components, deploying and operating the second drillstring in the borehole using the lightweight drill rig to perform core sampling.

In another aspect the present invention may be said to comprise a coupling for coupling: inner drill rods comprising a bore, and lightweight outer drill rods used in core drilling with a bore, to form a drillstring for fluid reverse circulation drilling comprising: a first coupling member for removable coupling to one end of an inner drill rod, a second coupling member for removable coupling to a second end of the inner drill rod, wherein the first and second coupling members centre the inner drill rod within an outer drill rod.

Optionally the core drilling is wireline core drilling and/or the lightweight drill rods are wireline core sampling drill rods.

Optionally the coupling further comprises a third member for removable coupling to the outer drill rod to retain either the first and/or second coupling member within the outer drill rod.

Optionally the third member is a coupling member that comprises the second coupling member as an inner coupling member and also comprises an outer coupling member.

Optionally the second coupling member forms part of an outer coupling member that comprises the second coupling member as an inner coupling member and also comprises an outer coupling. In another aspect the present invention may be said to comprise a coupling according to above wherein the second coupling member is further removably coupled to a first end of the outer drill rod, wherein the second coupling member comprises: an first inner coupling that removably couples the second coupling member to the second end of the inner drill rod, and a first outer coupling that removably couples the second coupling member the first end of the outer drill rod.

In another aspect the present invention may be said to comprise a coupling for coupling: inner drill rods comprising a bore, and lightweight outer drill rods used in core drilling with a bore, to form a drillstring for fluid reverse circulation drilling comprising: a first coupling member for removable coupling to one end of a first inner drill rod, a second coupling member for removable coupling to a second end of a second inner drill rod and respectively one end of each of first and second outer drill rods.

Optionally the core drilling is wireline core drilling and/or the lightweight drill rods are wireline core sampling drill rods.

In another aspect the present invention may be said to comprise a drill rod for assembly with other drill rods to form a drillstring used for fluid reverse circulation drilling comprising: an outer drill rod comprising a lightweight drill rod used in core drilling with a bore, an inner drill rod comprising a bore, a first coupling member removably coupled to one end of the inner drill rod, a second coupling member removably coupled to a second end of the inner drill rod and one end of the outer drill rod, wherein the first and second coupling members centre the inner drill rod within the outer drill rod.

Optionally the core drilling is wireline core drilling and/or the lightweight drill rods are wireline core sampling drill rods.

In another aspect the present invention may be said to comprise a method of RC drilling and core sampling comprising: assembling a first drillstring with dual walled drill rods according to any paragraph above and/or using the assembly method of any paragraph above, operating the first drillstring using a lightweight drill rig to perform fluid RC drilling, resulting in a borehole upon completion of RC drilling, extracting the drill string from the borehole, disassembling the drill rods of the first drillstring according to above, assembling a second drillstring with the outer drill rods, along with core sampling components, deploying and operating the second drillstring in the borehole using the lightweight drill rig to perform a core sampling.

In another aspect the present invention may be said to comprise a drill rod for assembly with other drill rods to form a drillstring used for fluid reverse circulation drilling comprising: a first and second outer drill rod, each comprising a lightweight drill rod used in core drilling with a bore, a first and second inner drill rod each comprising a bore, a first coupling member removably coupled to one end of the first inner drill rod, a second coupling member removably coupled to a second end of the second inner drill rod wherein the first and second coupling members centre the inner drill rods within the outer drill rods.

Optionally the core drilling is wireline core drilling and/or the lightweight drill rods are wireline core sampling drill rods.

Optionally a third member is provided that is removably coupled to the outer drill rods to retain either the first and/or second coupling members within the outer drill rods.

In another aspect the present invention may be said to comprise drill rod for assembly with other drill rods to form a drillstring used for fluid reverse circulation drilling comprising: a first and second outer drill rod each comprising a lightweight drill rod used in core drilling with a bore, a first and second inner drill rod each comprising a bore, a first coupling member removably coupled to one end of the first inner drill rod, a second coupling member removably coupled to a second end of the second inner drill rod and respectively one end of each of the first and second outer drill rods.

Optionally the core drilling is wireline core drilling and/or the lightweight drill rods are wireline core sampling drill rods.

It is intended that reference to a range of numbers disclosed herein (for example, 1 to 10) also incorporates reference to all rational numbers within that range (for example, 1, 1.1, 2, 3, 3.9, 4, 5, 6, 6.5, 7, 8, 9 and 10) and also any range of rational numbers within that range (for example, 2 to 8, 1.5 to 5.5 and 3.1 to 4.7).

The term "comprising" as used in this specification means "consisting at least in part of". Related terms such as "comprise" and "comprised" are to be interpreted in the same manner.

This invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more of said parts, elements or features, and where specific integers are mentioned herein which have known equivalents in the art to which this invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.

Brief description of drawings

Embodiments will now be described, with reference to the following drawings, of which:

Figure 1 shows a drill rig and drill string for fluid RC drilling.

Figure 1A shows an overview of a drill rod arrangement and coupling according to embodiments described.

Figure 2A shows a cut away view of an assembled dual walled drill rod.

Figures 2B and 2C show the first coupling member (box), second coupling member (pin) and third coupling member (connector) in further detail.

Figure 3 shows a dual walled drill rod arranged for coupling to a corresponding dual walled drill rod.

Figure 4 shows the first end of a first dual walled drill rod coupled to the opposite end of a second dual walled drill rod.

Figure 5 shows in diagrammatic form fluid RC drilling apparatus comprising a drill string made of the assembled dual walled drill rod.

Figure 6 shows in diagrammatic form one embodiment of a wireline retrievable core sampling assembly and of the direction of fluid flow in an assembled dual walled drill string of the present invention while in use downhole. Figure 7 shows an inner core barrel assembly with a latch head and drill bit arrangement used in conjunction with a fluid driven apparatus, such as that embodied in WO2015193799 for obtaining a core sample.

Figures 8 shows an example of a diamond coring bit as part of the inner core barrel in close up at the end of the core sampling assembly of Figure 7.

Figure 9 shows an example of the fluid flow through the arrangement of Figure 7.

Figure 10 shows an assembly of a drill rod for wireline core sampling and two piece coupling according to a second embodiment.

Figure 11 shows the internal taper thread (box) of a wireline core sampling rod at a first end.

Figure 12 shows the corresponding external reverse flank thread (pin) at a second end of a wireline core sampling rod, and the trapezoidal external thread of a different type of wireline core sampling drill rod for comparison.

Figure 13 shows a first coupling member of the second embodiment.

Figure 14 shows a second coupling member (combined outer coupling member) of the second embodiment.

Figure 15 shows a cross-section of a drill rod assembly with two drill rods coupled together.

Figure 15A shows a close-up of Figure 15.

Figure 16 shows the drill rod and outer coupling in further detail.

Detailed description of the invention

Overview

In overview, the embodiments described provide a dual walled drill rod for assembly with other such drill rods to form a RC drillstring 10 (see Figure 1) to be used for fluid reverse circulation (RC) drilling. These same dual walled drill rods can then be disassembled and parts of them used and assembled again to form a single wall drillstring 10' (see Figure 6) for core sample drilling. Thus an RC drillstring with dual wall drill rods as disclosed can be converted to a single walled drillstring with drill rods to be used for core sample drilling. Lightweight drill rods are used in the dual walled drill rods of the RC drillstring. This allows for a lightweight drill rig to be used for both drilling operations. This also allows for the dual purpose use of the same drill rods in both an RC drillstring and a wireline core sampling drill string. This in turn leads to efficiencies and/or advantages as described later.

Figure 1 shows in diagrammatic form a fluid reverse circulation (RC) drilling system, comprising a drill rig 15 and drillstring 10 as described herein to provide fluid reverse circulation (RC) drilling, in order to drill a borehole 11. Chip samples can then be obtained during the RC drilling process to be used for analysis of the formation. Referring to Figure 1A, each dual walled drill rod 12 comprises an inner drill rod 18 and an outer drill rod 17. An inner drill rod coupling 20 retains the inner drill rod within the outer drill rod. There might be one or more inner drill rod couplings, either separate or integrated, that achieve this (shown by dotted line). The inner drill rod coupling(s) 20 and an outer drill rod coupling 19 together couple a first dual walled drill rod to an adjacent dual walled drill rod, together forming part of an RC drillstring 10. Overall there might be two, three or even more couplings to enable assembly of a dual walled drill rod and/or couple/assembly each dual walled drill rod to another one to form a drill string.

Lightweight drill rods are used in the dual walled drill rods making up the RC drillstring 10. Due to the lightweight nature of the drill rods, the RC drillstring 10 can be operated by a lightweight diamond drilling/coring drill rig 15. Hereinafter, the drill rig will be referred to as a "lightweight drill rig". The RC drillstring for fluid RC drilling comprises a plurality of dual walled drill rods (e.g. 12) coupled together, the dual walled drill rods being those as described herein. The drillstring 10 can comprise other components for fluid RC drilling such as a fluid operated hammering apparatus 13 and a drill bit 14. Drillstrings and the components therein will be known to those skilled in the art.

As will be described later, the dual walled drill rods 12 comprise, among other things, a lightweight drill rod as the outer part of the drill rod. Any suitable lightweight drill rod could be used, typically those called "diamond drill rods" or "coring drill rods" or "wireline coring drill rods". The use of a lightweight drill rod 12 for RC drilling is (preferably) enabled through the use of a non-compressible fluid that activates a fluid activated apparatus such as a fluid activated hammer or vibrational apparatus, and carries the chips to surface (rather than using prior art pneumatic RC drilling that necessarily requires the use of heavy walled drill rods, large air compressors and heavy drill rigs). The use of such a lightweight outer drill rod provides a lightweight drillstring, which in turn can be operated by a lightweight drill rig.

The use of such a lightweight drill rig provides advantages in the coring field of use. The same type of lightweight outer drill rods can also be used for a coring drillstring 10' (see e.g. Figure 6) used in the coring process. That means, the same lightweight drill rig 15 and same outer lightweight outer drill rods can be used for coring and with the addition of an inner rod of the present disclosure can then be used for RC drilling.

So, referring to Figure 6, once the RC drilling process is completed, the RC drillstring 10 is disassembled, the outer drill rods liberated, and then those same outer drill rods are re-assembled into a single walled core sampling drillstring 10' so coring can take place to provide a more accurate analysis of the formation.

The drill rig does not have to be changed between the fluid RC drilling chip sampling process, and the core sampling process, and different drill rods are not required. This significantly reduces costs, improves safety through the use of lightweight drill rods and reduces time lost thus leading to greater overall efficiencies and improved safety.

Following from this, the present disclosure also describes a method of assembling multiple dual walled drill rods as disclosed herein, all of which can be assembled to form an RC drillstring 10. This can be connected to a lightweight drill rig for RC drilling. Then the method also comprises disassembling the RC drillstring, disassembling the dual walled drill rods, taking the liberated outer drill rods, and reassembling them into a single walled coring drillstring 10'. The coring drillstring 10' is coupled to the same lightweight drill rig for the coring process.

Particular non-limiting embodiments of the drill rods/drillstrings and their method of (dis)assembly and use will now be described.

First embodiment Figures 2 to 4 show a dual walled drill rod 240 according to the embodiments described that can be assembled with other such dual walled drill rods to form a RC drillstring 10 for fluid RC drilling.

Figure 2A shows a dual walled drill rod 240 with an undefined length, that can be screwed together (or unscrewed) with / from other such dual walled drill rods 240' (see Figures 3 and 4) to form a drill string 10 for fluid RC drilling. Reference herein to "drill rod" will mean the dual walled drill rod 12/240.

Drill rod 240 comprises a (lightweight) outer drill rod 241 ("host rod"). This is a wireline coring drill rod such as that typically used in diamond drilling and is lighter weight than that used in pneumatic RC drilling as the drill rod for fluid RC drilling only needs to carry fluid (such as drilling fluid such as mud), rather than contain the significant air pressures present in pneumatic RC drilling. Generally, when reference is made to a drill rod being lightweight, this means a lightweight drill rod e.g. for wireline core sampling that is lighter than conventional RC drill rods although still has sufficient strength to carry on its purpose. The lightweight drill rod can be made lighter through constructing the same from different materials, such as aluminium, lower grade steel, etc or the rod can still be made with the same materials as for an RC rod, such as steel, but the thickness is less. The weight differences can be as much as a 60% weight reduction although typically is around a 40-50% difference. The reason the drill rod can be made lighter is that the lightweight rod need only carry a fluid rather than have to withstand the significant air pressures experienced with the typically used pneumatic hammer for RC drilling. Examples of types of lightweight outer drill rods that can be used can be defined by one or more of the following characteristics

• A wireline coring rod designed for use with non-compressible drilling fluid.

• For use in diamond core drilling.

• Weights - e.g. about 47kg or less (compared with 67kgs for other types of RC drill rods).

• Examples of such lightweight wireline coring rods can be found in any one of the following technical specification sheets at

^■ Boart Longyear™ Coring Rods and Casing Catalog found at: http://app.boartiongyear.com/brochures/2016-Coring Rods Cataiog-F9.pdf. Fordia https://www.fordia.com/wp- content/uploads/2015/11/fichetechniquehuskya ngweb.pdf

^■ Di-Corp https://www.di-corp.com/products/view-product/deep- hole-wireline-drill-rodor Global Geotech https://www.globalgeotech.co.uk/drill-rods-casing-tubes.htm

• Note, the above are just examples and are not exhaustive of the types of lightweight drill rods that could be used with the present embodiments.

Examples of types of lightweight (wireline coring) outer drill rods that can be used are described with respect to the first embodiment. The outer drill rod 241 is a hollow cylinder/cylindrical wall with a bore. At one end of the outer drill rod 241 there is an internal thread 245A on the inner cylindrical surface, and at the other end of the outer drill rod there is a thread 245B on the outer cylindrical surface.

The drill rod 240 also comprises an inner drill rod 242 which is a hollow cylinder (tube)/cylindrical wall with a bore 243. Preferably the inner drill rod is also lightweight. At one end of the inner drill rod there is an internal thread 246A on the inner cylindrical surface, and at the other end of the inner drill rod 242 there is an external thread 246B on the outer cylindrical surface. Each end of the inner drill rod is removably coupled to first and second coupling members 247, 248. The first and second coupling members 247, 248 preferably have reciprocal couplings. Together, they can be considered a coupling for coupling adjacent dual walled rods. The first and second coupling members also provide some retention, as described below.

A first coupling member 247 is shown in Figure 2B in more detail. The first coupling member connects to and both aligns and locates (retains) the inner tube centrally within the inner diameter of the host rod and so has a retention function. It also doubles as a coupling member. The first coupling member comprises an inner cylindrical portion 250 axially aligned with an outer cylindrical portion 251 separated by an annular ring/boss 252 (also called "skirt"), to provide a first coupling member 247 with a bore 253. The inner cylindrical portion 250 has a smaller diameter than the outer cylindrical portion 251. The inner cylindrical portion 250 has an external thread 254 and forms a plug n for partial insertion into and coupling to the end of the inner drill rod 242 that has the internal thread 246A. The skirt 252 has an outer diameter that is commensurate with the inner diameter of the outer drill rod 241, although has openings to allow for fluid flow. This allows fluid flow/porting between the inner drill rod and the outer drill rod.

The openings could take various forms. For example, the skirt 252 could be of a generally annular ring with a diameter commensurate with the internal diameter of the outer drill rod 241, but is provided with apertures to allow for fluid flow. Alternatively, as shown, it could be an annular ring 252A with a smaller diameter, but with flanges 252B or other radial extensions that extend to the inner diameter of the outer drill rod 241, with the narrower annular ring 252A allowing for fluid flow. The outer cylindrical portion 251 has a stepdown portion/recess 257 for a seal 258 to provide a coupling. Alternatively there is provided another suitable configuration coupling on the internal diameter. The outer cylindrical portion 251 forms a socket for receiving part of a corresponding second coupling member on another dual walled rod.

A second coupling member 248 is shown in Figure 2C in more detail. Similarly this second coupling member connects to and both aligns and locates (retains) the inner tube centrally within the inner diameter of the host rod and so has a retention function. It also doubles as a coupling member. The second coupling member comprises a generally cylindrical portion 260 which at one end has a stepped recess 261 for coupling to the seal coupling 258 on the corresponding first coupling member 247 of another dual walled rod. The second coupling further has an internal step 262 leading to an internal thread 263 thus forming a box where the internal thread 263 can couple to the external thread 246B at the other end of the inner drill rod 242. The second coupling member 248 also comprises an annular ring/boss 264 (also called "skirt") at the threaded end 263, with a diameter greater than that of the external diameter of the cylindrical portion 260 and is approximately the diameter of the outer drill rod 241, so that when the second coupling member 248 is installed or threaded onto the inner drill rod, the annular ring 264 spans the annular gap 265 between the inner drill rod 242 and the outer drill rod outer 241. The annular ring has one or more apertures 266 for fluid flow.

The first and second coupling members can also be termed first and second inner drill rod coupling members (or just first and second inner drill rod couplings). The first and second coupling members in an alternative embodiment could be welded or otherwise joined together as one piece. In this case, they would be a single/unitary inner rod coupling member. The first and second coupling members 247, 248 can centre and align the inner drill rod 242 in an axial direction within the outer drill rod 241 to form the dual walled drill rod as shown in Figure 2A, and couple adjacent dual walled drill rods together as shown in Figure 3. The first coupling member 247 can be called a "box" and the second retention member a "pin" 248.

The dual walled rod also has a third (external) coupling member 270, which can be seen in more detail in Figures 2C and 4. The third coupling can also be termed the "outer rod coupling member" (or just outer rod coupling) The third coupling member takes the form of a cylindrical portion with an external threaded portion 271 at a first end, and an internal step 272 leading to an internal thread 273 at the second end. The third coupling member connects the first coupling member/second coupling member/inner drill rod assembly within the outer drill rod, and also couples adjacent dual walled drill rods, as shown in Figures 3 and 4. The third coupling member can be a "wireline coring rod joiner". Figure 3 shows two adjacent dual walled drill rods 240, 240' coming together, with a third coupling member being used for coupling, and Figure 4 shows the two coupled dual walled drill rods 240, 240' now joined. Both dual walled drill rods 240, 240' are the same as described herein. The external thread 271 of the third coupling member 270 can couple to the internal thread 245A of one end of an adjacent outer drill rod 241', and the internal thread 273 can couple to the external thread 245B on the end of the outer drill rod 241. Adjacent to the internal thread 273, the third coupling member has a recess 275 with no thread between the internal step 272 and the internal thread 273 that can receive the skirt of the second coupling member to assist with locating and centring the inner drill rod 242 within the outer drill rod 241 thus additionally retaining the inner rod in a manner to be described below. As such, the third coupling member can also act to retain.

Thus the first, second and third coupling members additionally all have a retention function for the dual walled rod. In some instances for ease of reference, the first coupling member could be a box, the second coupling member could be a pin and the third coupling member is a connector.

The first, second and third coupling members combine to form a three piece coupling.

For RC drilling, the dual walled drill rod 240 is assembled and an RC drillstring 10 assembled from such dual walled drill rods generally as follows. The order in which assembly takes place can change, although preferably when first assembling the first dual walled drill rod to go downhole, the bit is generally fitted with a first coupling member into which the second coupling member 248 can engage.

A diamond drilling contractor would have;

• Inner drill rods preferably A or B sized rods or at least rods that fit within a set of outer drill rods that are preferably lightweight.

• Outer drill rods - like the inners, the user may already have these, preferably the host rods are wireline coring rods (such as H size) that are preferably lightweight.

• First and second coupling members (box and pin) members for the inner rod (complete with seals)

• The third coupling member.

A user starts with a set of (lightweight) outer drill rods 241 and a set of inner drill rods 242 laid out on the ground. The user also has at hand a box 247, pin 248, and third coupling members 270. The user first takes an inner drill rod 242, and may place it on a table or other suitably height adjusted workspace, then a box member 247 and threads the external thread 254 onto the internal thread 246A of the inner drill rod 242. The user then takes a pin 248 and threads the internal thread 263 of the pin onto the external thread 246B of the other end of the inner drill rod 242. At this point the inner drill rod 242 has both a box and pin member on either end, forming an internal drill rod assembly. The skirt 264, 252 of the pin and box members extend radially from the inner drill rod 242. The user can then put an outer drill rod 241 onto the table. The user will then take the internal drill rod assembly (inner drill rod that has been fitted with the pin and box members), and slide the end with the box retention member 247 into the outer drill rod 241.

This internal drill rod assembly can then be pushed all the way through, until the skirt 264 of the pin 248 sits just proud of the outer thread 245B of the outer drill rod 241. At this point, the skirt 252 of the box member 247, should stop just short, or right at the beginning of the uphole internal thread 245A of the outer drill rod 241. The user can then take the third coupling member 270, place it over the protruding pin member 248 and screw it onto the external thread 245B on the outer drill rod 241. This now connects the internal rod assembly (including the inner drill rod) to the outer drill rod and retains it in place, such that the inner drill rod can no longer travel any further in the outer drill rod. This is because the skirt 264 of the pin member 248 is sandwiched in the recess between the external threaded outer end 245B of the outer drill rod 241 and the step portion 272 on the inner surface of the third coupling member 270. This is a first assembled dual walled drill rod 240 (RC rod set).

In an alternative method of assembly, when the user places the host rod on the table, the user can also take a third coupling and screw that onto one end of the host rod. Then the user can push the inner rod into the outer drill rod until the skirt 264 of the pin 248 butts against the internal shoulder 272 of the third coupling member. The user can then continue assembling the inner as described above.

Then another dual walled drill rod 240' can be assembled in the same way. The first assembled dual walled rod 240 can then be coupled to the second dual walled drill rod 240' by inserting the recessed end 261 of the pin member 248 on the first dual walled rod 240 into the sealing end portion 257' of the box member 247 in the second adjacent dual walled rod 240' and then screwing the internal thread 245A of the outer drill rod 241' second dual walled rod 240' to the external thread 271 of the third coupling member 270 on the first dual walled rod 240. In practice as the male/female threads 271/273 are engaged ends 261 and 258 are pulled together to create a seal. When removing the two rods, unscrewing them also pulls the joints 271 /273 and 261 and 258 apart. This is shown in Figures 3 and 4. This assembly process can then be repeated for further dual walled drill rods to assembly a drill string for RC drilling.

The third coupling member 270 centralises inner drill rod 242 within the outer rod 241 so that it is held in place and properly sealed (as everything is now seated and mated together). The third coupling member further forms part of the fluid flow path ensuring that the fluid going down hole and the chip laden fluid coming back hole does not intermingle (further explained below). The third coupling member 270 may also be slightly larger in diameter than the outer drill rods and can be designed to match the diameter of the bit. During use, the third coupling member 270 will centralise the outer drill rod within the bore and as it touches the sides of the bore hole, rather than the host rods, friction is reduced overall on the drill string, contributing to reduced wear and tear on the host rods, along with overall reduced costs. The third coupling member may be constructed from harder wearing material than the host rods or armoured with a protective coating or surface materials common in the industry to pro long the life of the third coupling member. Alternatively, the third coupling member is the same diameter size as the outer drill rod.

The lengths of the largest cylindrical member of the box member 247, extension portion of the pin member 248 and the third coupling member 270 are configured such that when everything is assembled, there is the correct spacing between the inner drill rod 242 and the outer drill rod 241 longitudinally so that everything fits together correctly.

The RC drillstring 10 assembled according to this embodiment can then be fitted to a diamond (lightweight) drill rig system, or similar. A bit box 14 (see Figure 5) would firstly be attached to the downhole end of a fluid activated apparatus, then the assembled dual walled drill rod is fitted to the top hole end of the fluid activated apparatus, this is then fed down and then another assembled dual walled drill rod is fitted to the top hole end of the prior assembled dual walled drill rod and so on, until bottom hole is reached and RC drilling can commence. This is more fully explained below. Optionally, the bit box is provided with a female engagement member.

In one use case for RC drilling, an assembled dual walled drill rod 240 would then be positioned into place above the bore hole with the pin member 248 facing downhole. It is held in place by the drill rig and then lowered downhole until the uphole end of the assembled dual walled drill rod 240 is sitting above the ground. It is then held in place. Then a second assembled dual walled drill rod 240', again with the pin member 248' facing downhole, is placed onto the drill rig and lowered downhole until it engages with the first assembled dual walled drill rod 240. The user can then tighten up the third coupling member 270. This process then continues on until the required length of drill string has been obtained. Drilling can then engage, where fluid is sent downhole - that is in between the cavity 265 created by the inside diameter of the outer drill rod 240 and the outside diameter of the inner drill rod 241 and as the skirt 264, 252 of the pin and box members have fluid flow holes, the fluid can flow down towards the bore face, where it can then return back uphole through the inner diameter of the inner drill rods of the drill string. To bring the dual walled drill rods 240 back uphole, the dual walled drill rods are bought up and disassembled in the opposite manner as they went downhole. The inner seals can be inspected, where a user can simply remove the seal if damaged and then re-insert a replacement seal 257. Similarly the connector 270 can be replaced as it wears out.

The third coupling member 270 does provide some additional length to the overall drill string length or combined assembled host rod lengths. This is insignificant. However the third coupling member does ensure the box and pin member couplings are seated and sealed to ensure the fluid does not leak out.

As discussed previously, a plurality of dual walled drill rods 240 can be assembled together into a RC drillstring 10 used in RC drilling, and then later disassembled to liberate the outer drill rods and allow assembly of a core sampling drillstring 10' to enable core sample drilling using the same lightweight outer drill rods. Once the fluid RC drilling is complete, the RC drillstring 10 is removed from the bore hole 11 and can then be disassembled into the individual dual walled drill rods 12/240. The individual dual walled drill rods are disassembled, in a manner that is reverse to the process of assembly. Once liberated, the outer drill rods 12/240 are made up into a core sampling drillstring 10'. The core sampling drillstring 10' is coupled to the same lightweight drill rig (as for the fluid RC drilling) 15 and the core sampling drillstring 10' is deployed into the bore hole and operated by the drill rig for core sampling in the usual way. A core sampling drillstring 10' assembly is shown diagrammatically in Figure 6. It comprises the repurposed outer drill rods 240 arranged into a drill string 10/200 within a bore 11. A hammer 13 and coring drill bit 14 and inner core barrel assembly 282 are assembled as part of the core sampling drillstring. Fluid flow 300 is shown by arrows in both Figures 6 and 9.

An example of a core sampling sub-assembly that is attached to the drill rods 240 outer rods 241 at the end of the drill string is shown in more detail with reference to Figures 7-9. This apparatus is described in the applicant's application WO201519193799 (an incorporated herein in its entirety by way of reference). Referring to Figures 7, 8 and 9, briefly, the core sampling sub-assembly 213 comprise an outer casing formed from a plurality of outer drill rods e.g. 240 coupled together (e.g., through threading). The outer forms part of the drill string 10/200. Figure 8 shows the end 210 portion of the apparatus in Figure 7 that is cut off in Figure 7. The outer drill rods 241 forming the drill string are rotated by an up hole drilling apparatus. A hammer or vibratory apparatus 280 with an outer tubular housing is coupled to the outer drill rods 240. The outer tubular housing is coupled to the outer drill rods 241 by the third coupling member 270. A section swivel 281 isolates the rotation of the hammer or vibratory apparatus 280 from the core barrel. This allows a core sampler barrel 282 to rotate relative/independently to the hammer or vibratory apparatus 280 and to isolate a core sample 283 in the barrel 282 from rotation that may damage the core sample. To extract a core sample 283, that has been obtained via core sample drilling, the apparatus is adapted to receive an extraction line and assembly that is lowered through the centre of the assembled outer drill rods using a cable wire 284 and couples to the extraction sub-assembly 213. The apparatus, including the drilling and hammering or vibratory operations, are effected by fluid flow from the drilling fluid. Figure 9 shows the drilling flow path 300, by way of example. The hydraulic power is converted into a rotational mechanical output by the rotational apparatus (e.g., by a turbine, PDM or the like) and then flows over/through/around the hammer or vibratory apparatus 280 and through to the drill bit.

Once the drill rods 241 are made up into a core sampling drillstring 10/200, the drillstring is coupled to the same lightweight drill rig (as for the fluid RC drilling)

15 and the drill rod is deployed into the bore hole and operated by the drill rig for core sampling in the usual way.

Second embodiment

A second embodiment is now described. This two piece coupling embodiment is simpler. Referring to Figure 2C, the reason is that in the three piece coupling the outer third coupling 270 at one end (see circle "A") abuts the base of the thread 245B of the outer rod directly, but the outer coupling 270 only abuts the outer drill rod 240 indirectly via the second coupling 275 at the end of the thread (see circle "B"). The stacked tolerances of the outer rod 240, outer third coupling 270 and second coupling 275 means that there can be some play/jiggle between coupled drill rods. The two piece coupling of this embodiment provides the same advantages as the first embodiment, plus some more advantages, including "double butting". The second embodiment uses just two couplings, not three. The second embodiment comprises a coupling where function of the third coupling member (outer drill rod coupling member) of the first embodiment has been integrated with the function of the first coupling member (first inner rod coupling member) of the first embodiment. This arrangement provides "double butting" whereby the outer drill rod 270 coupling member directly abuts the outer drill rod 240 at the thread base and the thread end (see circles "C", "D" in Figure 15A).

The embodiment will be further described.

Figure 10 shows an exploded dual walled drill rod 240' according to the second embodiment. It comprises a lightweight outer drill rod 241' ("host rod") such as previously indicated in the first embodiment, an inner drill rod 242', an inner drill rod coupling member 247' (also called an "inner rod adapter") and an outer coupling member 270', which is for coupling adjacent outer drill 240' rods and adjacent inner drill rods 242'.

Referring to Figure 10 and 15, the outer drill rod 241' is a hollow cylinder/cylindrical wall with a bore. At one end ("box end") of the outer drill rod there is an internal thread (box end thread) 245A' on the inner cylindrical surface, and at the other end ("pin end") of the outer drill rod there is an external thread (pin end thread) 245B' on the outer cylindrical surface. The box end thread 245A' has a central opening with a diameter slightly larger than the diameter of the bore to provide a step/abutment 297A to provide a stop for an outer coupling member 270' when it is threaded into the box end 245A'. Likewise, the pin end thread 245B' has a diameter slightly smaller than the diameter of the outer drill rod 241' to provide a step/abutment 297B to provide a stop when threaded to another outer coupling member 270'.

The outer drill rod 241' of the second embodiment is similar to that of the first embodiment, except that the external thread end (box thread end) 245A' and internal thread end (pin thread end) 245B' are reverse flank. This can be seen in Figure 12, which shows the external thread end 245B' of the wireline coring rod compared to that of the wireline coring drill rod 245B which is described in the first embodiment. This difference is not essential, and simply shows an alternative rod that could be used. Either embodiment could be used with any of the wireline coring rods described herein. The reverse flank external thread 245B' of the HRQ rod allows for a tighter fit and less axial movement when two outer HRQ rods are coupled together. Referring to Figure 11, the internal thread end 245A' has a complementary tapered configuration. This provides an advantage in downhole drilling operations where reduction of axial movement is preferable.

The inner drill rod 242 can be the same as used in the first embodiment, and has a hollow cylinder with a bore. The inner drill rod 242 can be placed inside the outer drill rod 241' to provide an annular gap. The inner drill rod has an internal thread end (box thread end) 246A and an external thread end (pin thread end) 246B, as previously described.

Referring to Figure 13, there is a first coupling member 247' (also termed "inner drill rod coupling member", "inner drill rod coupling" or "inner rod adapter") that comprises an elongated body cylindrical bore with a tapered end (pin end) 251' then moving to the left in the drawing, end 251' gradually steps up to a wider portion, a shaped flange boss 252'; and an external thread end (pin thread end) 254'. The wider portion between 251' and the flange boss 252' is bulked up to provide strength. A square or other shaped flange/boss 252' (also called a "skirt") extends from the elongated body between the tapered end 251' and the external thread end 254'. The first coupling member 247' couples to and both aligns and locates (retains) the inner drill rod 242 centrally within the inner diameter of the host rod 241' and so has a retention function. It also doubles as a coupling member that has a coupling function. The external thread end 254' forms a plug for partial insertion into and coupling to the internal thread end 245A' of the inner drill rod 241' that has the internal thread. The tapered end 251' is for insertion into an inner body 291 of an outer coupling member 270' as will be described below.

The skirt 252' has an outer diameter that is commensurate with the inner diameter of the outer drill rod 241', although is shaped differently (e.g. triangular, square, pentagonal, hexagonal, octagonal etc.) to the inner cross section of the outer drill rod 241' to provide channels/openings to allow for fluid flow. This allows fluid flow/porting between the inner drill rod and the outer drill rod. Alternatively, the skirt 252' could be of a generally annular ring with a diameter commensurate with the internal diameter of the outer drill rod, but is provided with apertures to allow for fluid flow. Alternatively, it could be an annular ring with a smaller diameter, but with flanges or other radial extensions that extend to the inner diameter of the outer drill rod, with the narrower annular ring allowing for fluid flow. Referring to Figure 14, there is a second coupling member 270' (outer coupling member or outer coupling). The second coupling comprises an inner coupling and an outer coupling which together perform similar functions to the second coupling and third coupling respectively of the first embodiment, but in an integral/unitary body.

The outer coupling member 270' will now be described in more detail. The outer coupling comprises an outer body 290, a concentric inner body 291 and an internal bore 298. The outer body 290 is configured with first and second outer couplings/threads 273', 271' (together forming the outer coupling) for coupling with outer drill 240'. For the first outer coupling 273', the outer body comprises a first internal thread at a first end (first outer coupling) 273' for coupling to the external tapered thread 245B' of an outer drill rod 241'. The first internal thread 273' comprises a tapered internal thread on a tapered internal surface of the bore complementary with the tapered external thread 245B' on an outer drill rod 241'. The tapered external thread coupling 273' has central bore/opening that leads into a cylindrical inner portion 290A of the outer body with a first diameter. There is a slight step/abutment 290B between the internal thread 273' and the inner cylindrical portion 290A due to their differing diameters, to provide a stop for the outer drill rod 241' that is threaded into the internal thread end 273'. For the second outer coupling, 271', the outer coupling comprises a first external thread at a second end (second outer coupling) 271' for coupling to the internal thread 245A' of an outer drill rod 241'. The external thread 271' comprises a tapered thread on a tapered external surface of the body of the coupling complementary with the tapered internal thread 245A' on an outer drill rod 241'.

The inner body 291 is configured with first 292 and second 293 inner couplings for coupling an inner drill rod 242 and an inner drill rod coupling 247'. The first inner coupling 292 comprises an internal thread (box thread) 299 at a first end (first inner coupling) for coupling to the external thread 246B of an inner drill rod 242. The inner body 291 also comprises second inner coupling 293 at a second end (second inner coupling) for coupling to the end 251' of an inner drill rod coupling 247'. The end 293 is profiled with an annular rebate 294 for a ring seal 295, a first cylindrical portion 293A of a first diameter for receiving the end of the inner drill rod coupling, and stepping down to a second cylindrical portion 293B with a second diameter for fluid flow. There is a step/abutment 293C formed between the first cylindrical portion 293A and the second cylindrical portion 293B, all together this provides part of the bore of the overall outer coupling member 270', along with the cylindrical inner portion of the outer body and the central opening of the tapered internal thread. The inner body 291 in effect performs the function of the second coupling 248 (second inner coupling member) of the first embodiment, but it has been integrated with/into the outer coupling member 270'. This overcomes the problem of stacked tolerances as explained earlier.

Channels 296 are provided between the inner body 291 and the outer body 290 to allow for fluid flow between the outer body and the inner body. The fluid flow channels lead into the inner cylindrical portion of the outer body. Fluid flow can also occur through the bore.

Figure 15 shows two partial dual walled drill rods assembled together, comprising outer drill rods 241', the inner drill rod coupling 247' and the outer drill rod coupling member 270'. Figure 16 shows the outer drill rod coupling member 270' and outer drill rod 241' in more detail, in assembled and exploded form.

Figure 15 shows a first partial outer drill rod 241', with its external threaded tapered end 245B' threaded to the internal threaded end 273' of an outer drill rod coupling member 270', and is positioned such that the annular end surface of the outer drill rod abuts against the step/abutment 290B of the inner cylindrical portion of 290A of the outer body 290 of the outer coupling member 270'. This provides a double abutment on both shoulders of the thread, reduced axial movement of the two components and greater torque and tensile load capacity of the thread joint. The external threaded tapered end 271' of the outer drill rod coupling member 270' is threaded to the internal threaded end 245A' of a second outer drill rod 241'. The outer coupling member 270' is positioned such that the annular end surface of the outer coupling at the external thread end 271' abuts against step/abutment of the thread/bore boundary of the outer drill rod. This provides for reduced axial movement of the two components and greater torque and tensile load capacity of the thread joint.

A first inner drill rod 242, disposed through/inside the first outer drill rod 241' but axially offset extends out of the outer drill rod and into the outer drill rod coupling member 270', where the external threaded end 246B' of the inner drill rod 242 is threadedly coupled to the inner thread 273' of the inner body 291 of the outer coupling member 270'. The inner drill rod 242 is positioned such that the annular end surface of the inner drill rod abuts against step/abutment 290B of the inner cylindrical portion 290A of the outer coupling member 270'. This provides an abutment shoulder for reduced axial movement of the two components. An inner drill rod coupling member 247' is coupled to the outer coupling member 270' by way of the end 251' of the inner drill rod coupling 247' and the bore 293 of the outer coupling member 270'. A ring seal 295 is provided in the ring seal annular rebate 294 to provide for sealing.

The internal thread box end 246A of a second inner drill rod is coupled to the external thread pin end 254' of the inner drill rod coupling member 247'. The annular end surface of the inner drill rod coupling abuts against the stop/abutment of the internal thread box end of the inner drill rod. The second inner drill rod 242 is positioned through/inside the first outer drill rod 241' but axially offset to extend out of the outer drill rod 241' and into the second inner drill rod coupling 247'. The flange 252' of the inner drill rod coupling 247' fits against the inner surface of the bore of the outer drill rod 241' to retain the second inner drill rod 247' in place both concentrically and/or axially. The shape of the flange 252' allows for fluid flow around the flange. See Figures 14, 15, 15A for fluid flow "F" whereby drilling fluid flows through the annular gap between the inner 242' and outer drill 241' rods, around the flange 252' (see Figure 15) of the inner coupling 247' and through the outer coupling member 270' channels 296 (as shown in Figures 14, 15) and back through the middle of the drill rod 240.

A second inner drill rod coupling 247' is shown at the left hand end of the first dual walled drill rod 241', ready for retaining and receiving the inner drill rod 242 and outer coupling member 270' of an adjacent dual walled rod assembly 240', and for retaining the inner drill rod 242 in place. Likewise, a second outer coupling member 270' is shown at the right hand end of the second dual walled drill rod 240' ready for inserting into an inner drill rod coupling 247' in an adjacent dual walled rod assembly 242'.

Advantages

Like the first embodiment, a method of assembly of the dual walled drill rod 240' will be described. This is in the same use context, where an operator wants to assemble a drillstring 10 for RC drilling using the dual walled drill rods 240' of the present disclosure. A dual wall rod is assembled, and then coupled to another dual walled rod. This is continued until there is a drillstring 10 of the desired length for RC drilling. When RC drilling is complete, each dual walled drill rod is first removed from the drill string, and then disassembled into constituent components. Then the same outer drill rods are coupled to assemble a drill string for core sampling.

The method of assembly will now be described in more detail. For RC drilling, the dual walled drill rod is assembled generally as follows where the order in which assembly takes place can change,

A diamond drilling contractor would have;

•

• Inner drill rods preferably B sized rods or at least rods that fit within a set of outer drill rods that are preferably lightweight.

• Outer drill rods - like the inners, the user may already have these, preferably the host rods are wireline coring rods that are preferably lightweight.

• First coupling members/inner drill rod coupling members for the inner rod

• Second coupling members/outer coupling members.

A user starts with a set of (lightweight wireline coring rods) outer drill rods and a set of inner drill rods laid out on the ground. The user also has at hand first and second coupling members, which the user can place on a table or other easily accessible place.

The user first takes the outer coupling member and places it in vice or similar device that is at a suitable height adjusted workspace. The user then takes the inner rod and screws the pin end of the inner rod into the inner coupling box end (292) of the outer coupling member. The user then takes the inner drill rod coupling member and screws the pin end of the inner drill rod coupling member into the box end of the inner drill rod. The user can then take a spanner or other tool and tighten the now assembled outer coupling member, inner drill rod and inner coupling member together by using the spanner on the flange (252') of the inner coupling member and tightening the same together. (Remember the outer coupling member is still retained by the vice). Once tightened, then the outer drill rod, is picked up by a driller where the pin end of the outer drill rod (245b') is firstly passed over the inner drill rod coupling member and then is screwed into the outer box end of the outer coupling member (273') to ensure there is double abutment against edges 297b and 290b. A seal can be placed into the female portion of the inner bore/recess of the outer coupling member. This dual walled rod is then coupled to a previously assembled dual wall rod on the drillstring, by threading the exposed internal thread box end of the outer drill rod to the external thread pin end of the outer coupling of the dual walled drill rod on the drillstring, and push the end of the inner drill rod coupling member into the inner body of the outer coupling on the dual walled drill rod on the drillstring.

Then another dual walled drill rod 240' can be assembled in the same way and attached to the drill rod in the same way.

The drill string 10 assembled according to this embodiment can be fitted to a diamond drill rig system, or similar. A bit box 14 (see Figure 5) would be firstly put into position at the end of the outer drill rod or other drill string assembly. Generally the bit box is provided with a female engagement member.

Variations

The three piece coupling could be used with the HRQ rods and/or the two piece coupling could be used with the HQ rods. But preferred performance comes from the two piece coupling with the HRQ rods.

The couplings or variations thereof could be used with other drill rods. Those described and the related embodiments are examples only.

One or more of the following advantages can be experienced from one or more of the embodiments described.

With prior art pneumatic RC drilling, high pressure air is pumped from surface down the drill rod - the air energises a pneumatic hammer which crushes the rock - and the rock chips are blown to the surface up through an annulus in the drill bit and pneumatic hammer and up through the centre annulus of the drill rods - for analyses by a geologist. As previously described, the drill rods used in this application need to be made of a heavy wall steel tube - (as they are in effect energy storage devices) as compressed air expands dangerously and if a rod fails this can be extremely dangerous. The weight of the RC drill rods dictate that large powerful drill rigs are used, along with very large powerful air compressors. The deeper the hole - the more weight of rods that are down hole, thus the bigger the rig needs to be, to be able to pull the rods back out of the hole. Further, the air pressure required increases with the depth of the hole - thus the deeper the hole, the greater the air pressure required, therefore bigger compressors are needed and the requirement for ever increasing heavy weight drill rods and larger drill rig etc.

In contrast, the present embodiments relate to fluid RC drilling, which optionally may be used with the applicant's fluid driven hammer and fluid driven vibration technologies (the applicant's technologies includes both a Mechanical Force Generator or Magnetic Force Generator (e.g. magnetic hammer is or similar see for example W02009/028964, W02012/002827 or Mechanical Force Generator or similar see for example W02012/120403, WO2015/193799 or Magnetic Force Generator or similar see for example WO2012/161595)) that all use a non- compressible drilling fluid (instead of air) to energise the down hole reverse circulation and hammer/vibration apparatus, with the cutting samples being carried to surface from the drill bit - through the centre of the hammer/vibration apparatus to surface via the drilling fluid through the dual walled drill rods for analyses. Fluid does not get compressed in the same way air does in this process. Given the fluid driven systems as described, the drill rods for fluid RC drilling no longer need large heavy walled drill rods due to the non-compressible drilling medium being used. As a result, fluid RC drilling that preferably utilises such fluid driven hammers or fluid driven vibration apparatus no longer require large drill rigs with expensive and dangerous air compressors. The present applicants have determined that this opens up the potential for lightweight drill rigs and drill strings (e.g. like those for diamond drill rigs for core sampling) to drill deep holes fast (fluid RC drilling) while recovering a non-contaminated chip sample for mineral analyses, with significant operational advantages such as for example,

• Easier and cheaper to mobilise drill rigs

• Safer to use (no compressors / dust)

• Far less fuel burn (no compressors and smaller rigs)

• A fluid driven hammer or fluid driven vibration apparatus is not depth limited (pneumatic RC systems require ever increasing volumes of compressed air as they get deeper, as well as struggling when ground water is encountered, it is uncommon for an air RC system to drill deeper than 500 meters). • Simple fast to assemble / disassemble

• Inner drill rods securely held

• The complete assembly becomes a lightweight RC drill rod - the light weight is due to the fact that these RC rods are only for use with drilling fluid (not compressed air) therefore the outer rods (HQ or otherwise) are not an energy storage device, and can be much lighter than air RC drill rods. (47KGs vs 67KGs)

• This in turn means better safety for staff.

• Drill rigs can drill deeper, due to a lighter drill rods

• The third coupling member of the first embodiment can have a larger outside diameter than the outer drill rod, giving the following benefits; o acts as a stabiliser to reduce rod vibration / hole deviation o reduces friction (less wall contact) o enhances the life of the drill rod (only the third coupling members are rubbing on the bore wall - these can then be replaced as necessary).

• The third coupling member if the first embodiment further enables the box and pin members to be fully seated and engaged with one another, ensuring no intermingling of the fluid flow coming downhole and that of the fluid returning uphole, further there is no escape of the same out into the bore hole.

A preferred drill bit to be used in the present invention is the applicant's own hybrid drill bit embodied in W02018/116140, which is incorporated herein in its entirety by way of reference.

It is further appreciated, that fluid driven hammers and fluid driven vibration apparatus are a recent technology from the present applicants. To date there is no lightweight dual walled reverse circulation drill rods available and certainly not for use on a diamond drill rig. The present applicants have determined how to adapt existing lightweight coring drill rods to be suitable for use as dual walled lightweight drill rods for reverse circulation.

"Diamond" drill rigs that use lightweight drill strings with diamond bits for core sampling are the mainstay of mineral exploration, whereby a high-quality rock core sample can be obtained for mineral analyses. The embodiments described herein use such lightweight drill rods which then enables the use of lighter drill rigs than those used in pneumatic RC hammers. By way of example - a conventional 3.5" pneumatic air RC drill rod weighs approx. 67kgs. The same sized lightweight diamond drill rod will weigh 47kgs. On this weight difference alone a diamond drill rig will be able to drill approx. 42% deeper than the equivalent conventional RC Rods on a pneumatic hammer. This provides significant operational, safety and cost savings.

In particular, the present applicants have devised how to utilise single walled lightweight (e.g. "diamond") drill rods, in conjunction with a securely held (but easily removable) inner rod that enables the thin walled diamond drill rod to be quickly and safely modified into a dual walled lightweight RC drill rod (for use with a fluid hammer or fluid driven vibration apparatus)

The benefit of this approach is that, a lightweight (e.g. "diamond") drill rig (that being a drill rig capable of rotating thin walled rods to enable the capture of a rock core sample) is now able to drill deep into the earths (rock) formations with the fluid driven hammer or fluid driven vibration apparatus, while capturing samples rock cuttings in real time for analyses.

Furthermore, once a mineral zone of interest is located, then the fluid driven apparatus and dual walled RC rods can be withdrawn from the ground, the inner rod can then be easily removed, a core sampling barrel attached to the end of the (now) single walled rods, and the coring assembly (using wireline retrievable and/or other systems as are commonly used) can now be lowered down the existing bore hole and operated using the existing lightweight drill rig until they reach the depth where the fluid RC drilling was terminated, and as the core drilling advances - intact core sample can now be retrieved for analyses.

Normally this process might require two different drill rigs - one large, heavy and expensive to carry out the air RC drilling, and then a second lighter (diamond drill rig) would be mobilized to take the core samples. Each drill rig would have its own drill rods specific to the function being done.