WO2021105910A1

WO2021105910A1 - Improvement relating to drill rods

Info

Publication number: WO2021105910A1
Application number: PCT/IB2020/061162
Authority: WO
Inventors: Owen SCHICKER; Gareth LYONS
Original assignee: Flexidrill Limited
Priority date: 2019-11-27
Filing date: 2020-11-26
Publication date: 2021-06-03
Also published as: US20220412176A1; AU2020393176A1; CA3158102A1

Abstract

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 bore that is tapered at each end, an inner drill rod within the outer drill rod, and a retention member removably coupled to each end of the inner drill rod to retain the inner drill rod between the tapered ends of the outer drill rod.

Description

IMPROVEMENT RELATING TO DRILL RODS Field of the invention

The present invention relates to fluid RC drilling, core sampling and dual walled drill rods for use in fluid RC drilling that can then be converted to drill rods for core sampling.

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 in a formation after the initial borehole has been collared to prevent hole collapse. One of the two processes is reverse circulation (RC) drilling 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 after the zone of interest in the formation has been reached using the RC drilling process, although in some instances the driller may decide to just use core drilling. 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, 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, 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 strong materials, such as steel or the like, that then makes the drill rods heavy therefore the drillstring becomes 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. 67 Kgs per 3 metre length. So, for a 250m drillstring, the drill rods alone weigh approximately 5600kg. As a result, the drillstring is very heavy and 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 the high pressures are not present, the drill rods used are light weight, typically approx..

40kg per 3meter length, consequently the drillstring is lighter (3333kg 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 objection of the invention to provide a drill rod for that can be converted from a drill rod RC drilling to a drill rod for core sample drilling and/or associated apparatus formed from the drill rod.

In another aspect the present invention may be said to comprise a drill rod for assembly with other drills 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 that is tapered at each end, an inner drill rod within the outer drill rod, and a retention member removably coupled to each end of the inner drill rod to retain the inner drill rod between the tapered ends of the outer drill rod.

Optionally the retention member comprises a first retention member coupled to a first end of the inner drill rod, and a second retention member coupled to a second end of the inner drill rod. Optionally the first and/or second retention member comprises: a coupling by which the retention member can be removably coupled to a respective end of the inner drill rod, and a radially extending abutment configurable to abut on a respective taper of the bore, the abutment comprising: a fixed portion with a diameter less than the smallest diameter of the bore, a deployable element to extend the diameter of the abutment greater than the smallest diameter of the bore.

Optionally: the fixed portion of the abutment comprises two or more radial arms, the deployable element comprises at least one element in in each radial arm that can deploy from the radial end of the arm.

Optionally the element deploys when the inner drill rod is coupled to the retention member.

Optionally the outer drill rod is a lightweight drill rod.

Optionally the outer drill rod is a diamond drill rod, coring drill rod, H rod or the like.

Optionally the inner drill rod inner has an outer diameter less than the smallest diameter of the bore of the outer drill rod.

In another aspect the present invention may be said to comprise a retention member for a drill rod for assembly with other drill rods to form a drillstring used for fluid reverse circulation drilling comprising: a coupling by which the retention member can be removably coupled to an end of an inner drill rod, and a radially extending abutment configurable to abut on a respective taper of a bore of a lightweight outer drill rod, the abutment comprising: a fixed portion with a diameter less than the smallest diameter of the bore, a deployable element to extend the diameter of the abutment greater than the smallest diameter of the bore.

Optionally the element deploys when an inner drill rod is coupled to the retention member.

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 "drillstring" used for fluid reverse circulation drilling, the method comprising taking an outer drill rod comprising a bore that is tapered at each end and: doing one of: coupling a first retention member to a first end of an inner drill rod, the first retention member having a radially extending abutment with a deployable element, and inserting the first retention member and inner drill rod into the bore of the outer drill rod, or inserting a first retention member into the bore of the outer drill rod, the first retention member having a radially extending abutment with a deployable element, and inserting an inner drill rod into the bore of the outer drill rod and coupling the inner drill rod to the first retention member, and deploying the deployable element of the radially extending abutment of the first retention member, coupling a second retention member to a second end of the drill rod, the second retention member having a radially extending abutment with a deployable element, and deploying the deployable element of the radially extending abutment of the second retention member.

Optionally the dual walled drill rod is anyone of those in the statements 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 of the statements 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: undeploying the deployable element of the radially extending abutment of the second retention member, and removing the second retention member from the bore of the outer drill rod, and one of: undeploying the deployable element of the radially extending abutment of the first retention member, and removing the inner drill rod and first retention member from the bore of the outer drill rod.

In another aspect the present invention may be said to comprise method of RC drilling and core sampling comprising: assembling a first drillstring with dual walled drill rods according to any statement above and/or using the assembly method of any statement 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 any statement 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.

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 2 shows a dual walled drill rod in generic form.

Figure 3 shows a first embodiment of an assembled dual walled drill rod.

Figures 4-6 shows a first embodiment of the dual walled drill rod in the uphole, neutral and downhole positions to illustrate the inner rod "float" when the retention members (24A and 24B) of Figures 7A and 7B are attached.

Figure 7A, 7B show first and second embodiments of a retention member for the dual walled drill rod.

Figure 8 shows an inner drill rod of the dual walled drill rod.

Figures 9 to 13B show stages of an assembly of a dual walled drill rod.

Figure 14 shows a tool for assembling the dual walled drill rod.

Figures 15 to 19 show stages of an alternative assembly of a dual walled drill rod.

Figure 20 shows in diagrammatic form one embodiment of a 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 21 shows in diagrammatic form a core catcher and drill bit arrangement used in the core sampling assembly of Figure 20.

Figures 22A, 22B shows an example of a core catcher barrel and drillstring assembly.

Figure 23 shows an example of fluid flow through a core catcher barrel and drillstring assembly

Detailed description of embodiments Overview

The embodiments described provide a dual walled drill rod for assembly with other such drill rods to form a drillstring to be used for fluid reverse circulation (RC) drilling. These same dual walled drill rods can then be disassembled to be used again in wireline core sample drilling. So these drill rods are a hybrid drill rod that can be converted from a dual wall drill rod for assembly for RC drilling to a lightweight drill rod to be used for wireline core sample drilling.

Figure 1 shows in diagrammatic form a drill rig 15 and drillstring 10 to provide fluid reverse circulation (RC) drilling, in order to drill a borehole 11. Chip samples can be obtained during the RC drilling process that are then used for analysis of the formation. Once the RC drilling process is completed, coring can take place to provide a more accurate analysis of the formation (using the outer drill rods of the rods used in RC (i.e., removal of the inner) drilling to make up a separate drillstring for coring as described later).

Due to the lightweight nature of the drill rods, the drillstring 10 is operated by a lightweight diamond drilling/coring drill rig 15. Hereinafter, the drill rig will be referred to as a "lightweight drill rig". The 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 "wireline core sample drill rods", "diamond drill rods", "coring drill rods", drill rods having an "internal upset" or are "double butted" where "butted" means the bore of the drill rod is tapered at both ends. The use of a lightweight drill rod (e.g. wireline core sample drilling rod) for RC drilling is enabled through the use of a 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 pneumatic RC drilling that uses heavy walled drill rods 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 be used for both the fluid RC drilling process and the coring process. That means, the same lightweight drill rig and same outer lightweight drill rods can be used for coring and with the addition of an inner rod of the present invention can then be used for RC drilling. The drill rig does not have to be changed between the fluid RC drilling chip sampling process, and the core sampling process. This significantly reduces costs and time lost thus leading to greater overall efficiencies.

Figure 2 shows in general diagrammatic form a dual walled drill rod 12 according to the embodiments described that can be assembled with other such dual walled drill rods to form a drillstring 10 for fluid RC drilling. Reference herein to "drill rod" will mean the dual walled drill rod 12.

Drill rod 12 comprises a (lightweight) outer drill rod 20 ("host rod") that is 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 drill rod designed for use with non-compressible drilling fluid. • For use in diamond core drilling.

• Weights - e.g. about 40kg or less (compared with 75kgs 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.boartlongyear.com/brochures/2016- Coring_Rods_Casing-Catalog-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 o 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.

A particular non-limiting example could be as follows:-

• H rod .

• V wall rod with a bore of the rod with an internal taper. The bore is "internally upset" or "double butted". "Butt", means that the ends of the rod are tapered.

• Designed for use with non-compressible drilling fluid.

• For use in diamond core drilling.

• Weights - e.g. 40kg (compared with 67kgs for other types of RC drill rods).

• Generally, an H rod is 3.5 inches in diameter and fits/suits the "chuck drive" on a diamond drill rig. The chuck drive is a hollow spindle that generally has 5-7 teeth internal of the spindle that hydraulically grip/grab the rod at the top of the hole to provide Weight On Bit (WOB) and rotation to the rods in use. Also, the diamond drill rig, may have a "foot clamp" that is designed to fit/receive these H rods at the base of the rod.

For example, a "H-wireline coring rod with an internal upset" could be used. "Upset" refers to the internal diameter ends of the rod being thicker than the majority of the body of the rod.

The taper or upset serves the purpose of thickening the rod at either end to enable functional threads (male and female) to be made to allow suitably strong connections of the rods together. The outer drill rod 20 is a hollow cylinder/cylindrical wall with a bore 21. The bore 21 has a varying diameter, and comprises:

• a (preferably fixed diameter) central section 21A,

• a varying diameter tapering section 21B, 21C extending from each end of the central section, each taper section leading to a

• a (preferably fixed diameter) end section 21D, 21E, leading to a

• bore opening 20A, 20B at each end of the outer drill rod.

The diameter of the central section 21A is larger/wider than the diameter of the two end sections 21D, 21E/bore openings 20A, 20B (which are smaller/narrower than the diameter of the central section). The tapered sections 21B, 21C are shown exaggerated in Figure 2 for clarity. In practice, that taper is much smaller but sufficient to allow the machining of the threads.

The dual walled drill rod has an inner drill rod 22 which is a hollow cylinder (tube)/ cylindrical wall with a bore 23. Each end 22A, 22B of the inner drill rod is removably coupled to a retention member 24. In the preferred embodiment, there are two retention members 24A, 24B that differ slightly to have reciprocal couplings. Reference to retention member 24 can mean either of these variations. The retention member 24 comprises a radially extending stop/abutment 25 (25A, 25B), a first coupling configured for coupling to one end of the inner drill rod 22, and a second coupling configured for coupling to an end of a corresponding retention member of an adjacent dual walled drill rod (e.g. 12 A - see Figure 1) to which the dual walled drill rod will be coupled. The radially extending abutments 25A, 25B comprise fixed portions 26A, 26B (collectively referred to as 26) having a diameter less than the narrowest/smallest diameter of the outer drill rod bore (being the diameter of the opening 20A, 20B/end section 21D, 21E) of the bore) and it has deployable portions (element) 27A, 27B (collectively referred to as 27) that extends from the diameter of the abutment 25A, 25B to be greater than the smallest diameter of the outer drill rod bore. The deployable portion 27 could be any suitable element such as a ball, but other options are possible also, such as rods, springs, cam rollers, lobes or the like.

When a retention member 24 is coupled to each end of the inner drill rod 22, and the deployable portion 27 is deployed, the diameter of the radially extending abutment 25 will be greater than that of the narrowest diameter 21D, 21E of the bore 21 of the outer drill rod. This means that the inner drill rod 22 will be retained within the outer drill rod 20 and between the narrow openings/end sections as the radially extending abutment will prevent the inner drill rod extending past the tapered sections 21B, 21C at either end of the outer drill rod bore 21. When abutment 25 abuts the tapered section, it could be deemed to be seated, and the abutment could also be considered a "seat". The term "seat" and "abutment" can be used interchangeably in this specification in relation to this component of any of the embodiments of the retention member. The radially extending abutment 25 will not necessarily touch or engage with the tapered sections, although it can do so. This allows the inner drill rod to have a freedom of movement (tolerance) to "float" between the two end sections 21D, 21E within the bore 21 to prevent the inner rod damaging the two end sections when the dual walled drill rod is vertical and assembled into a drillstring. The "float" or range of movement is dictated in part by the uphole connections, such as the drill rig 15 and downhole connections, such as the hammer 13 and bit 14. Having this float/tolerance allows the inner rods a range of movement to accommodate these uphole and downhole connections, that also takes into account any manufacturing tolerances of the outer drill rods when placed into the vertical position. This then allows the abutments to seat into the tapered sections without damaging them. It should be noted that the inner rod is non-rotationally linked to the outer - so when the outer rods are being tightened up or twisted together, it does not interfere with the inner rods.

The dual walled drill rod 12 is assembled generally as follows. First, an outer drill rod 20 is taken. Then, a first retention member 24A, a second retention member 24B and the inner drill rod 22 are assembled in a suitable sequence and inserted into the outer drill rod bore 21 in a suitable sequence. The deployable portion 27A, 27B is deployed to retain the inner drill rod 22 within the outer drill rod 20. In one possible embodiment, deployment is achieved by partially coupling the inner drill rod 22 to the first retention member 24A and placing the assembly into the outer drill rod 20, then deploying the deployable portion 27A so that the retention member 24A seats within the tapered section 21B and therefore inner drill rod 22 cannot go past the end section 21D of the outer drill rod 20. The second retention member 24B is placed into the outer drill rod bore 20 and coupled to the inner drill rod 22, and the deployable portion 27B is deployed, so that the inner drill rod 22 and second retaining member 24B seats within the tapered section 21C and therefore cannot go past the end section 21E of the outer drill rod 20. It will be appreciated that there are many other arrangements, and sequences and methodologies for assembling the inner drill rod within the outer drill rod. Some will be described in further detail later. A plurality of such a dual walled drill rods 12 can be assembled, and then they can each be assembled with an adjacent dual walled drill e.g. 12A rod to create a drillstring 10.

Example embodiments

A detailed description of one possible example embodiment of the lightweight dual walled drill rod will now be described with reference to Figures 3 to 8.

Figure 3 shows an assembly of the dual walled drill rod 12, itself coupled to two adjacent identical dual walled drill rods 12A, together forming part of a drillstring 10.

The drill rod 12 comprises an outer drill rod 20 which is a hollow cylinder/cylindrical wall with a bore 21. The bore comprises a central section 21A of fixed diameter extending to a narrowing tapered section 21B, 21C of reducing diameter at each end of the central section 21A, and each tapered section extending to an end section 21D, 21E with an opening 20A, 20B (see Figure 2). The end section and opening are of a fixed diameter that is smaller/narrower than the central section 21A diameter. Each end 20A, 20B of the outer drill rod 20 comprises an internal thread 31A, 31B or other coupling section for coupling to an adjacent drill rod 12A.

The drill rod further comprises an inner drill rod 22 formed of a hollow cylinder with a bore 23 of fixed diameter (seen in more detail in Figure 8). Each end 22A, 22B of the inner drill rod comprises an outer/external thread 32A, 32B or other coupling for coupling the respective end of the inner drill rod to a respective retention member (e.g. spigot) 24A, 24B.

There are two types of retention members 24A, 24B, each for coupling to an opposite end 22A, 22B of the inner drill rod. The retention members 24A, 24B can be seen in more detail in Figures 7A, 7B. A first retention member (variation/embodiment - see Figure 7A) comprises a hollow cylinder/cylindrical body 71A with a bore 72A that forms an extension section. A radially extending abutment 25A protrudes radial from one end of the cylindrical body 71A. The abutment has a hollow central portion 74A that provides an opening to the bore 72A of the cylindrical body. The retention member comprises a first coupling 73A (for example at a first end) in the form of an internal thread or other suitable coupling for connection to the external thread 32A or other coupling of the inner drill rod. The first coupling 73A is preferably provided within the bore 72A of the cylindrical body, although this is not essential. The retention member comprises a second coupling 75A (for example at a second end) in the form of a bayonet or other suitable coupling for coupling to a corresponding second retention member 25B on an adjacent drill rod 12A. The second coupling is preferably provided at the end of the cylindrical body away from the radially extending abutment, but this is not essential. Further provided about the second coupling is a seal 33A to be received within a cavity 34A or the like that retains the seal. The seal 33A can be more clearly seen in Figure 9.

The radially extending abutment 25A comprises a plurality (preferably four) of lugs e.g. 76A that extend radially from the cylindrical body and are spaced such that there are gaps 77A between adjacent lugs. The gaps allow fluid flow either up or downhole, preferably downhole. Each lug 76A has a spherical cavity 78A for receiving a deployable ball 27A. Each cavity 78A comprises ball opening 79A on the internal surface of the central opening 74A of the abutment with a diameter greater than the diameter of the ball to allow insertion of the ball, and retention opening 70A on the outer surface of the lug 76A with a diameter that is less than the diameter of the ball so that the ball can protrude through the opening, but cannot pass through the opening so the ball is retained in the cavity. Further retention of the ball can be aided by the provision of an CD- ring 80A (see Figure 9) or the like within the spherical cavity 78A to prevent the ball falling out. In a manner to be described more fully later, upon full insertion and coupling of the inner drill rod 22 to the retention member 25A, the deployable ball in each lug will deploy by partially extending through the retention opening on the outer surface of the lug.

A second retention member 25B (variation/embodiment - see Figure 7B) is provided, which is configured in the same as the first retaining member 25A, except that the second coupling 75B (for example at a second end) is in the form of a socket for receiving the bayonet coupling 75A of the first retention member. On the bayonet coupling being received within the socket, the seal 33A sealingly engages to the internal diameter of the socket 72B to prevent fluid escaping. The reference numerals in Figure 7B suffixed with "B" correspond to the same reference numerals in Figure 7A suffixed with "A" for the same feature (e.g. 71A, 71B), or a feature which is not the same, but is similar or corresponding (e.g. 72A, 72B). More generally, a reference with no suffix can be used as shorthand to refer to either retention member embodiment.

When fully assembled, the retention members 24 and inner drill rod 22 sit within the bore 21 of the outer drill rod 20. In particular, the assembly sits movably within the central 21A and tapered sections 21B, 21C of the bore 21. The deployable balls 27A,

27B are deployed such that they protrude through the cavity retention openings in the lugs and provide a deployed diameter of the retaining member abutment that is larger than the diameter of the end sections/openings of the outer drill rod bore. This means that the inner drill rod cannot move past the tapered sections 21B, 21C of the outer drill rod bore 21 and therefore is retained there within. As the first and second embodiments 24A, 24B of retention members work together in this fashion, together they can jointly be considered a "retention member". The cylindrical body 71 (comprising 71A, 71B) of each retention member 24 has a diameter that is narrower than the diameter of the end section/opening of the outer drill rod bore, and therefore the cylindrical body 71 can extend therethrough. The cylindrical body 71A of the first retention member 24A is dimensioned so that it in fact extends through and beyond the opening of the outer drill rod bore so that it can extend into the opening of the bore of an adjacent drill rod and its bayonet 75A can couple to the socket 75B of the cylindrical body 71B of the second retention member 24A of the adjacent drill rod 12A. Likewise, the cylindrical body 71B of the second retention member 24B is dimensioned so that it extends into the opening of the outer drill rod bore 21 and the socket coupling 75B can receive the bayonet coupling 75A of the corresponding retention member 24A of a corresponding adjacent drill rod 12A.

Figures 4 to 6 show how the inner drill rod 22 and retention member assembly 24 is retained within the outer drill rod bore 21, yet can move longitudinally within the central 21A and tapered sections 21B, 21C. During operation, the drillstring 10 is vertical and dependent on the uphole and downhole connections the inner drill rod 22 and respective retention member assemblies 24A, 24B can move uphole or down hole due to the "float" (that is, tolerance/built in allowed range of movement) to some degree within the bore 21 of the outer drill rod 20. Figure 4 shows the inner drill rods/retention member assembly floating towards uphole (left hand side of the figure), such that the uphole abutment 24A is within the tapered section 21B and the downhole abutment 24B is within the central section 21. Figure 5 shows the assembly floating in a neutral position, such that both the uphole abutment 24A and downhole abutment 24B sit on the boundary of the respective tapered sections 21B, 21C and central section 21A. Figure 6 shows the inner drill rods/retention member assembly floating towards downhole (right hand side of the Figure), such that the uphole abutment 24A is within the central section 21 and the downhole abutment 24B is within the downhole tapered section 21C. This movement into, at and out of the respective tapered sections depends upon the uphole (drill rig 15) and downhole connections (hammer 13 and bit 14). Method of assembly and disassembly of the dual walled drill rod

A method of installing the retention members to an inner drill rod that is also installed into the outer drill rod to assemble the dual walled drill rod will now be described in detail. It will be appreciated that the order and sequence is one example only, and others will be envisaged by those skilled in the art.

Referring to Figure 9, a first end of an inner drill rod 22 is threadedly coupled to the threaded first coupling 73A inside the retention member 24A. However, at this point the inner drill rod 22 is only partially threaded on, so that some of the external thread 32A (see Figure 8) on the inner drill rod is still exposed within the retention member central opening 74A. This means that the full diameter/width of the inner drill rod is not positioned concentrically between the deployable balls, so as not to deploy them. Rather, the slightly narrower threaded portion 32A is concentrically between the spherical balls, so does not deploy the balls such that the balls are still flush inside the retention member. This means the radially extending abutment has a diameter that is less than the diameter of the end section/bore opening to the outer drill rod so that the retention member and inner drill rod can slide into the outer drill rod bore. In this case the first embodiment of the retention member 24A with a bayonet (second) coupling 75A is shown, but the process could equally apply to the second embodiment of the retention member 24B with the socket (second) coupling 75B.

Referring to Figure 10, next, the retention member 24A/inner drill rod 22 assembly is inserted (with the retention member leading) into an outer drill rod 20 in direction A. A castellated tool 140 (such as shown in Figure 14) or other suitable tool is used to rotate, tighten and fully couple the inner drill rod and the retention member. Referring to Figure 14, the castellated tool has a hollow cylindrical body with cut-outs and turrets at one end to form the castellation. At the opposite end the body is provided with a pair of complementary flat sides 141 and a slot into which an actuation handle 142 is provided. The tool is inserted into the bore 21 of the outer drill rod 20 into the gap between the inner drill rod 22 and the outer drill rod 20 and the castellations of the tool align and engage in the lugs/gaps between the lugs of the retention member. The castellated tool can then be held still by the use of a spanner or the like that grips the flat sides of the tool, the inner drill rod can then be rotated to fully engage the remaining thread of the inner rod bringing the two together into a full coupling position. In this position, the full outer width/diameter of the inner drill rod 22 moves into position concentrically within the abutment opening 74A and between the balls. This movement deploys the deployable balls, so they protrude through the retention openings in the lug. This can be seen in Figure 10 where the balls are now deployed within the bore wall 21A and inside the tapered section 21C.The abutment 25A is now in the fully deployed configuration such that its diameter is now larger than the diameter of the end section 21B, 21C/ openings 20A, 20B of the outer drill rod bore 21.

Referring to Figure 11, the inner drill rod is then pushed further, again in direction A, into the bore of the outer drill rod until the thread or other coupling on the other end of the inner drill rod is just exposed. Referring to Figure 12, next a retention member according to the second embodiment 24B is coupled to the exposed thread 32B of the inner drill rod 22. Again, at this point the inner drill rod 22 is only partially threaded on, so that some of the external thread on the rod is still exposed within the retention member 24B. This means that the full width of the inner drill rod 22 is not positioned concentrically between the deployable balls, so as not to deploy them. Rather, the slightly narrower threaded portion is concentric with the balls, so does not deploy them. This means the radially extending abutment has a width/diameter that is less than the diameter of the end sections 21B,21C/opening 20A, 20B of the outer drill rod 20. In this case the second embodiment of the retention member 24B with a socket coupling 73B is shown, but the process could equally apply to the first embodiment of the retention member. In the preferred embodiment, a first embodiment of the retention member is coupled to one end, and a second embodiment of the retention member is coupled to the opposite end.

Referring to Figures 13A and 13B show the opposite ends of an assembled lightweight dual walled drill rod of the present invention where Figure 13A shows retention member 24A with the bayonet coupling and Figure 13B shows retention member 24B with the socket coupling. In order to ensure the retention members are seated correctly between the tapered sections, the inner rod 22/retention member 24A/24B assembly is then pushed further into the outer drill rod bore 21 until the first embodiment retention member 24A resides in the tapered portion 21B of the bore. The first retention member cannot push past the tapered portion because the deployed balls provide an abutment with a width/diameter that will not pass through the smaller diameter of the uphole end section 21B/opening 20A of the bore. However, the second embodiment of the retention member 24B coupled to the other end of the inner drill rod 22 has not yet been deployed and will pass through the end section 21C/opening 20B at the other downhole end of the outer drill rod 20 and will not sit within the tapered section 21C of the outer drill rod bore 21 until the inner drill rod is fully threaded into the retention member 24B. With reference to Figure 13B and 14, the castellated tool 140 is then slid over the cylindrical body 71B of the second embodiment of the retention member 24B and castellations of the tool align and engage in the lugs/gaps between the lugs of the retention member. To ensure that the retention members are located correctly within the inner drill rod the edges 143 of the handle 142 of the tool sits flush against the end 50 of the outer drill rod. A second castellated tool is then slid over the cylindrical body of retention member 24A. Correct location is necessary to ensure the balls are deployed in the right position and that no damage is caused to the tapered sections of the outer drill rod. The first castellated tool can then be rotated with the handle to rotate the retention member relative to the inner drill rod to thread the two together into a full coupling position. In this position, the full outer width/diameter of the inner drill rod moves into position concentrically in the abutment opening between the balls thus pushing the deployable balls, so they deploy and protrude through the openings in the lug. The abutment is now in the fully deployed configuration such that its diameter is now larger than the diameter of the end section 21C/opening 20B of the downhole end of the outer drill rod bore 21. Referring to Figures 13A,13B, the inner drill rod/retention member assembly is now retained within the tapered sections of the outer drill rod bore, and the dual walled drill rod is ready for coupling to other such drill rods to form a drillstring. The rods can be disassembled in the reverse manner as described further below.

As noted earlier, there are a range of different sequences that the assembly could occur in. For example, an alternative is described briefly here with respect to Figures 15 to 19. Referring to Figure 15, the first embodiment of the retention member 24A is slid into the outer drill rod bore 21, and then referring to Figure 16, the inner drill rod 22 is inserted into the drill rod bore and coupled to the second embodiment of the retention member. The inner drill rod is fully coupled so that the deployable balls of the abutment deploy into their extended position (which can be better seen in figure 18). In a similar manner, the second embodiment of the retention member is coupled to the other end.

Once the drill rods 12 are made up into a drillstring 10 they are placed on the lightweight drill rig 15 for fluid RC drilling. Referring to Figures 4-6 , when a drillstring 10 containing the rod 12, 12A etc is lifted from horizontal to vertical, the balls engage in the tapered downhole section 21C of the drill rods to stop them from dropping out. Preferably, the balls 27A, 27B interlock against the taper - and support the weight of the inner drill rod 22. The downhole connection such as the hammer and/or bit may cause the inner rod to move back uphole to thus engage with the tapered section 21B. The float allows for this movement to occur and has no effect on mud flows. There could be multiple ball packs spaced evenly around the abutment in the lugs of the inner rod (four are shown, but other numbers are possible) to keep the lower end of the inner rod concentric to the outer rod. Referring to Figure 20, there is shown in schematic a drillstring made up of multiple rods where drilling mud is pumped from surface down the annulus between the inner and outer rod to energise a hammer. The fluid can then jettison out above the bit into the space between the outer drill rod and the bore hole, where it can then travel down to the bore face where the fluid then picks up the cuttings which is then returned to surface via the drill bit - through the hammer and up through the centre tube to surface for analyses. It can equally be envisaged that the fluid coming down hole could jettison out through the face of the bit and return uphole between the cavity of the hole and outer drill string.

Preferably, the balls do not touch the tapered sections 21B, 21C until moved up or down hole from centre. Their purpose is to stop the inner drill rod falling out once the rod assembly is lifted into position to be fitted into the drill string. They do not locate the inner rod axially. Location of the inner rod is determined by the up and down hole connections, for example a fluid hammer such as for example a magnetic hammer as further described below.

Yet other variations of the assembly are possible. For example, the first and second embodiment of retention members could be attached to the inner drill rod and the entire assembly put into the bore of the outer drill rod, then the first and second embodiment of the retention members are deployed to retain the assembly in place.

Once the fluid RC drilling is complete, the drillstring 10 is removed from the bore hole 11 and can then be disassembled into the individual dual walled drill rods. The individual dual walled drill rods are disassembled, in a manner that is reverse to the process of assembly.

Briefly, the second embodiment of the retention member is partially unthreaded from the inner drill rod using the castellated tool so that the inner drill rod retracts from the concentric position between the deployable balls, so that the balls can retract back into the undeployed position. This can be termed "undeploying" the balls. While the balls do not necessarily retract back at that point (they can retract back later when coerced by the taper) they are in a position where they can retract back. The assembly is then partially pulled out of the outer drill rod. Because the balls can retract back, the second embodiment of the retention member can slide through the smallest diameter bore portion of the outer drill rod and be extracted therefrom. The second embodiment of the retention member is then fully decoupled from the inner drill rod using the castellated tool. Next, the inner drill rod is partially unthreaded from the first embodiment of the retention member using the tool so that the inner tube retracts from the concentric position between the deployable balls so that the balls can retract back into the undeployed position. This can be termed "undeploying". The assembly is then pulled out of the outer drill rod. Because the balls can retract back, the first embodiment of the retention member can slide through the smallest diameter bore portion of the outer drill rod and be extracted therefrom. The first embodiment of the retention member is then fully decoupled from the inner drill rod using the castellated tool. The outer drill rod can then be repurposed for use in a drillstring for core sampling by coupling to other such drill rods to form a core sampling drillstring.

As noted earlier, there are a range of different sequences that the assembly and disassembly could occur in.

Once the drill rods 12 have been disassembled, the outer drill rods 20 are repurposed (converted) for core sampling, by assembling them into a core sampling drillstring assembly 200. A core sampling drillstring assembly is shown diagrammatically in Figure

20. It comprises the repurposed outer drill rods 20 arranged into a drillstring with a bore

21. A hammer 13 and coring drill bit 14 and inner core barrel assembly 210 are assembled as part of the core sampling drillstring. The inner core barrel assembly 210 and drill bit 14 are shown in more detail in Figure 21 diagrammatic form. Fluid flow is shown by arrows in both Figures 20 and 21.

An example of a core sampling sub-assembly that is attached to the outer rods 20 at the end of the drill string is shown in more detail with reference to Figures 22A, 22B and 23. This apparatus is described in the applicant's application WO201519193799 (and incorporated herein in its entirety by way of reference). Referring to Figures 22A, 22B and 23, briefly, the core sampling sub-assembly comprises an outer casing formed from a plurality of outer drill rods 20 coupled together (e.g. through threading). The outer casing is or forms part of a drill string. Figure 22B shows the end portion of the apparatus in Figure 22A that is cut off in Figure 22A. The outer drill rods 20 forming the drill string 200 is rotated by an up hole drilling apparatus 15. A mechanical force generator (hammer) 13 with an outer tubular housing is coupled to the outer drill rods 20. The outer tubular housing is coupled to the outer drill rods 20 by threading or other coupling means. A section swivel 211 isolates the rotation of the rotational apparatus /mechanical force generator 13 from the core barrel 210. This allows the inner core barrel assembly 210 to rotate relative/independently to the mechanical force generator 13 and to isolate the core sample 212 in the barrel 210 from rotation that may damage the core sample. To extract a core sample 212, 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 20 using a cable wire 214 and couples to the extraction sub-assembly 213. The apparatus, including the drilling and hammering operations, are effected by fluid flow from the drilling fluid. Figure 23 shows the drilling fluid flow path, 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 mechanical force generator 13 and through the drill bit.

Once the drill rods 12 are made up into a core sampling drillstring, 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.

Advantages of embodiments described

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 = 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 has been made possible 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 pressurised 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 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).

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

Fluid driven hammers and fluid driven vibration apparatus are a recent technology from the present applicants (primarily due to the massive challenges of enabling a hammer or vibration apparatus to operate with modified drilling fluids (drilling mud)). To date there is no lightweight dual walled reverse circulation drill rods available. The present applicants have determined how to adapt existing lightweight wireline core sampling drill rods to be suitable for use as dual walled lightweight drill rods for reverse circulation. As an example, "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" air RC drill rod weighs approx. 67kgs. The same size diamond drill rod, will weigh 40kgs, so a drill will be able to drill approx. 85% deeper (than they would by using air RC Rods), providing significant operational, safety and cost savings.

In particular, the present applicants have devised how to utilise single walled lightweight (e.g. "diamond") drill rods/wireline core sampling drill rods, in conjunction with a securely held (but easily removable) inner rod with a threadably energised mechanism that enables the thin walled diamond drill rod to be quickly and safely modified into a dual walled light weight 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 would 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 would 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.

Claims

1. 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 bore that is tapered at each end, an inner drill rod within the outer drill rod, and a retention member removably coupled to each end of the inner drill rod to retain the inner drill rod between the tapered ends of the outer drill rod.

2. A drill rod for assembly with other drills 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 that is tapered at each end, an inner drill rod within the outer drill rod, and a retention member removably coupled to each end of the inner drill rod to retain the inner drill rod between the tapered ends of the outer drill rod.

3. A drill rod according to claim 1 or 2 wherein the retention member comprises a first retention member coupled to a first end of the inner drill rod, and a second retention member coupled to a second end of the inner drill rod.

4. A drill rod according to any preceding claim wherein the first and/or second retention member comprises: a coupling by which the retention member can be removably coupled to a respective end of the inner drill rod, and a radially extending abutment configurable to abut on a respective taper of the bore, the abutment comprising: a fixed portion with a diameter less than the smallest diameter of the bore, a deployable element to extend the diameter of the abutment greater than the smallest diameter of the bore.

5. A drill rod according to claim 4 wherein : the fixed portion of the abutment comprises two or more radial arms, the deployable element comprises at least one element in in each radial arm that can deploy from the radial end of the arm.

6. A drill rod according to claim 5 wherein the element deploys when the inner drill rod is coupled to the retention member.

7. A drill rod according to any preceding claim wherein the outer drill rod is a lightweight drill rod.

8. A drill rod according to any preceding claim wherein the outer drill rod is a diamond drill rod, wireline coring drill rod, H rod or the like.

9. A drill rod according to any preceding claim wherein the inner drill rod inner has an outer diameter less than the smallest diameter of the bore of the outer drill rod.

10. A retention member for a drill rod for assembly with other drill rods to form a drillstring used for fluid reverse circulation drilling comprising: a coupling by which the retention member can be removably coupled to an end of an inner drill rod, and a radially extending abutment configurable to abut on a respective taper of a bore of a lightweight outer drill rod, the abutment comprising: a fixed portion with a diameter less than the smallest diameter of the bore, a deployable element to extend the diameter of the abutment greater than the smallest diameter of the bore.

11. A retention member according to claim 10 wherein: the fixed portion of the abutment comprises two or more radial arms, the deployable element comprises at least one element in in each radial arm that can deploy from the radial end of the arm.

12. A drill rod according to claim 11 wherein the element deploys when an inner drill rod is coupled to the retention member.

13. A method of assembling a dual walled drill rod for subsequent assembly with other drill rods to form a "drillstring" used for fluid reverse circulation drilling, the method comprising taking an outer drill rod comprising a bore that is tapered at each end and: doing one of: coupling a first retention member to a first end of an inner drill rod, the first retention member having a radially extending abutment with a deployable element, and inserting the first retention member and inner drill rod into the bore of the outer drill rod, or inserting a first retention member into the bore of the outer drill rod, the first retention member having a radially extending abutment with a deployable element, and inserting an inner drill rod into the bore of the outer drill rod and coupling the inner drill rod to the first retention member, and deploying the deployable element of the radially extending abutment of the first retention member, coupling a second retention member to a second end of the drill rod, the second retention member having a radially extending abutment with a deployable element, and deploying the deployable element of the radially extending abutment of the second retention member.

14. A method according claim 13 wherein the dual walled drill rod is anyone of claims 1 to 9

15. A method of disassembling a dual walled drill rod, being a drill rod of any one of claims 1 to 9 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: undeploying the deployable element of the radially extending abutment of the second retention member, and removing the second retention member from the bore of the outer drill rod, and one of: undeploying the deployable element of the radially extending abutment of the first retention member, and removing the inner drill rod and first retention member from the bore of the outer drill rod.

16. A method of RC drilling and core sampling comprising: assembling a first drillstring with dual walled drill rods according to any one of claims 1 to 9 and/or using the assembly method of any one of claims 1 to 14. 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 the claim 15, 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.