The present invention relates to downhole tools used in wellbores, and, in particular, to downhole tools used in rotary operations .

A number of different types of downhole tools and equipment are used in the oil and gas exploration and production industry during the drilling of a wellbore, lining of the drilled bore with a metal casing/liner, and in the subsequent completion of the well to gain access to subterranean hydrocarbon bearing rock formations .

These tools and equipment- include, for example, drill strings used in the drilling of a wellbore; stabilisers and centralisers used for centralising equipment in a borehole or downhole tubing; reamers and other cutting tools used for reaming a drilled borehole wall; and cleaning tools used for cleaning downhole tubing preparatory to completion of a well or in an intervention procedure.

In the oil and gas exploration industry, numerous wellbores are drilled and maintained with the assistance of different types of downhole tools. Such tools are mounted on or incorporated into a string for use in various well bore operations. Such a string could for example be a drill string where it is be usual for the string to be rotated within the well bore. Another tubular string commonly encountered in such operations is a casing string.

In drilling operations, bottomhole assemblies are provided toward the downhole end of the string and are typically provided with stabiliser tools. These stabilisers provide a stand-off of the string from the wellbore walls as their outer surface is juxtaposed the wellbore walls. Stabilisers help to keep the drill pipe or heavyweight drill pipe and drill collar from the well bore wall reducing friction, maintain the drill bit in the correct position within the wellbore, and thus help to maintain torque on the drill bit.

Known drill string stabilisers are typically cylindrical tubular elements which are fitted around the drill pipe or provided integrally with the pipe, and often include grooves to allow fluid to pass relatively unrestricted upwards through the well borehole. Some known stabilisers have helical groove channels extending around the body of the pipe.

In a similar fashion, drill collars of a bottomhole assembly may carry integral stabiliser arrangements of a similar structure, or a stabiliser arrangement of this type may be provided above the drill bit, for a similar

purpose of helping to remove fluid and debris away from the drill bit or a drill shoe of the assembly and along the wellbore annulus to surface.

Grooved stabiliser elements are also used during reaming, which is either a secondary drilling process for re- entering an existing wellbore, for example for enlarging the wellbore diameter, or for ensuring a drilled borehole is of a desired diameter.

Cleaning tools are also often applied at various points on the string and are provided with a scouring or scraping outer surface for removing residue from the insides of the wellbore walls or inside walls of casing.

Strings run in casing are typically equipped with protecting sleeves. Further, casing strings are provided with tubular centralisers that keep the casing central in the wellbore with an annular space between the outer surface of the casing and the wellbore walls.

The downhole tools and various string elements must be constructed such that they can withstand the forces that they may be subjected in a wellbore whilst performing their specific functions within the string. Ideally, the elements are able to function while other wellbore procedures are carried out simultaneously, thus maximising efficiency. During operation of a string in a wellbore, fluid is typically pumped down through the centre of the string at pressure causing the fluid to return back up through the outer wellbore annulus flushing out cuttings and debris. It is therefore important for a stabiliser tool used during drilling to

accommodate the passage of drilling fluid from the rotating drill bit through the annulus between the wellbore wall and the string. Similar performance is required of cleaning tools, centralisers and other downhole tools.

Typically, in drilling and cleaning operations, a particular tool is designed and configured for a specific task in a wellbore. Indeed, for drilling, stabilising, centralising and clean-up operations, the tools may be of a specific outer diameter corresponding to the inner diameter of the bore or casing in which they are run. When the wellbore has sections at depths of decreasing inner diameter, it may be necessary to remove the tool and replace with a different tool of appropriate dimensions.

Such downhole tools are often incorporated as individual sections into a string. Changing out tools that have become worn or introducing new tools to the string to deal with unexpected problems can therefore result in a lengthy and costly operation. It is desirable to be able to expeditiously react and replace and introduce tools as required in the field.

Various proposals for downhole tools have been documented that address some of the above issues. United States Patent number US 4,190,124 (Taylor) provides details of a stabiliser with blades that are removable. The blades fix into longitudinal slots provided on planar components of the stabiliser main body. The planar components are surfaces extending longitudinally and which are effectively ridges with corresponding low relief valley

channels formed in between and allowing fluid to flow past.

International Patent Publication Number WO 91/05936 (Weatherford) discloses a centraliser, stabiliser, or pipe protector having a fluted tubular cylindrical outer surface that directs and channels fluid flow upwards through the wellbore. The channels may create a helical path for the fluid. Protruding ribs create an annular space between a string and the wellbore wall and enhance turbulence of the fluid and material flowing past the exterior surface of the device.

Further proposed systems include a downhole tool for cleaning operations having detachable cleaning pads. These are fastened in place with a nut and bolt. The purpose is to be able to quickly replace worn brushes should it be necessary during operations. The cleaning pads may be equipped with brushes or scrapers .

Although prior art systems have addressed some important issues, problems persist with current equipment causing much downtime during drilling operations. One particular such problem during rotary drilling is differential sticking of the pipe to the wellbore wall, which is particularly common when drilling through clay rich formations and when well pressure is greater than formation pressures. Further, such formations cause 'balling', which is the effect of solids such as clays sticking to various tool components due to pressure effects. These effects prevent the tools from operating properly and may drive the drill string to a halt.

It is therefore desirable to provide a downhole apparatus that obviates or at least mitigates some of the drawbacks of associated with prior art downhole tools and methods.

It is amongst the aims and objects of the invention to provide a downhole apparatus capable of providing a body upon which a variety of tool assemblies can be configured.

According to a first aspect of the invention, there is provided multi-function downhole apparatus comprising: a tubular main body; at least one recess formed in an outer surface of the body, the recess adapted to receive each of a set of interchangeable tool elements, wherein the set of interchangeable tool elements comprises any two of a stabiliser blade, a cleaning element, and a roller reaming tool element.

In this context, the term cleaning element should be construed broadly and includes elements, components or assemblies providing a cleaning, scraping, scouring, or brushing function in a wellbore. This includes debris or junk collection elements, and magnetic components configured for junk or debris collection.

According to a second aspect of the invention, there is provided a method of configuring a multi-function downhole apparatus, the method comprising the steps of: - Removing a first tool element from a recess in a tubular body; - Removably attaching a second tool element, different from the first, to the recess in the tubular body;

Wherein the first and second tool elements are any two selected from a stabiliser blade, a cleaning element, and a roller reaming tool element.

The method allows the same tubular body to be configured as a cleaning tool, a stabiliser tool, or a roller reaming tool .

The tool may comprise a first set of recesses circumferentially distributed around the body.

In one embodiment, the tool comprises a second set of recesses circumferentially distributed around the body in a location longitudinally displaced from a first set of recesses on the body.

Preferably, the second set of recesses is rotationally offset with respect to the first set of recesses. In this way, the first and second set of recesses together provide an increased circumferential coverage of the tool elements when the tool is being run in the wellbore.

In one embodiment, the tool comprises a magnetic tool element. The magnetic tool element may be received in the recess. The radial dimension of the magnetic tool element may be less than the depth of the recess such that the outer surface of the magnetic tool insert is inset with respect to the outer dimension of the apparatus. In this way, the apparatus provides a pocket for the collection of debris, junk and cuttings from the wellbore.

According to a third aspect of the invention, there is provided a method of configuring a downhole apparatus, the method comprising the steps of: - Removing a first tool element from a recess in a tubular body; - Removably attaching a second tool element to the recess in the tubular body; Wherein the first tool element is a stabiliser blade having a first radial dimension for running in a wellbore of first inner diameter, and the second tool element is a stabiliser blade having a second radial dimension, different from the first, for running in a wellbore of second inner diameter.

The method allows the same tubular body to be used as a stabiliser tool in wellbores, casings and linings of different inner diameter.

According to a fourth aspect of the invention there is provided downhole apparatus comprising: a tubular main body; at least one recess formed in an outer surface of the body, the recess adapted to receive a removable tool element; wherein the body is provided with at least one bore for coupling a removable tool element, and the bore is aligned on an attachment axis inclined with respect to a radial axis of the body.

Preferably, the recess is formed to extend radially of the body. More preferably, the apparatus is adapted to receive a removable tool element extending radially of the body.

By inclining the attachment axis the need to provide a screw or bolt extending the entire depth of the removable tool element is avoided. In addition, the attachment axis can be aligned such that forces encountered during wellbore operations have an increased axial component.

According to a fifth aspect of the invention there is provided a downhole assembly comprising: a tubular main body; at least one recess formed in an outer surface of the body; a plurality of interchangeable tool elements comprising of any two of selected from group of: a stabiliser blade of a first radial dimension, a stabiliser blade of a second radial dimension, a cleaning element, and a roller reaming tool element; wherein the recess is adapted to receive the each of the plurality of interchangeable tool elements during a different mode of operation.

According to a sixth aspect of the invention there is provided a downhole assembly comprising: a tubular main body; at least one recess formed in an outer surface of the body; a removable tool element; wherein the body is provided with at least one bore for coupling the removable tool element to the body, and the bore is aligned on an attachment axis inclined with respect to a radial axis of the body.

According to a seventh aspect of the invention there is provided a downhole assembly comprising: a tubular main body; at least one longitudinal recess formed in an outer surface of the body; a removable tool element received in the recess and upstanding from the outer surface of the main body; wherein the removable tool element has an outer surface comprising an upper portion and a side wall portion, and the removable tool element is attached to the main body via a bore extending from the side wall portion, through the removable tool element, and into the main body.

Preferably, the bore is aligned on an attachment axis inclined to a radial axis of the tubular body.

Preferably, the tubular body of any of the first to seventh aspects of the invention is provided with a plurality of elongate ribs upstanding from an outer surface of the main body and extending at least part way along a length thereof. More preferably, the recess is formed in an outer surface of the rib.

The recess may be aligned with the longitudinal axis of the tubular body.

Preferably also, adjacent pairs of ribs defining a flow channel therebetween for flow of a downhole medium along the body. The ribs may be aligned substantially parallel to a longitudinal axis of the body. Advantageously, the ribs are shaped such that at least one dimension of each channel is non-uniform.

The tubular body may further comprise at least one flow guide located adjacent an end of the channel, the flow guide and the channel together defining a flow path for flow of a downhole medium along the body.

According to an eigth aspect of the invention, there is provided a downhole tool comprising: a tubular main body having at least one recess formed in an outer surface of the body, the recess adapted to receive, when the apparatus is in a first configuration, a stabiliser blade of a first radial dimension, and is adapted to receive, when the apparatus is in a second configuration, a stabiliser blade of a second radial dimension.

According to a ninth aspect of the invention there is provided downhole apparatus comprising: a tubular main body; a plurality of elongate ribs upstanding from an outer surface of the main body and extending at least part way along a length thereof, adjacent pairs of ribs defining a flow channel therebetween for flow of a downhole medium along the body; wherein at least one rib is provided with a longitudinal recess formed in an outer surface of the body, the recess adapted to receive a removable tool element.

Preferably, the ribs are aligned substantially parallel to a longitudinal axis of the body. More preferably, the ribs are shaped such that at least one dimension of each channel is non-uniform.

According to a tenth aspect of the invention, there is provided a multi-function downhole apparatus comprising:

a tubular main body having at least one recess formed in an outer surface of the body, the recess adapted to receive, when the apparatus is in a drilling configuration, a first interchangeable tool element for use in a drilling operation, and is adapted to receive, when the apparatus is in a wellbore clean-up configuration, a second interchangeable tool element for use in a wellbore clean up operation.

It will be appreciated that the apparatus of all aspects of the invention may be provided as an integral part of the tool or tubing string, or as a separate component adapted to be coupled to tubing, a tool string or sections of a tubing string such as a length of casing. In particular, the apparatus may be formed as an integral part of a tool string component, and may indeed form an integral part of a drill pipe section.

There will now be described, by way of example only, embodiments of the present invention with reference to the following drawings, of which:

Figure IA is a perspective view of apparatus in accordance with a first embodiment of the invention;

Figures IB and 1C are respectively side and plan views of the apparatus of Figure IA;

Figure 2A is a perspective, partially exploded view of a stabiliser assembly consisting of the apparatus of Figure 1 and removable stabiliser blades;

Figures 2B and 2C are respectively side and plan views of the assembly of Figure 2A;

Figure 3 is a perspective view of a cleaning assembly consisting of the apparatus of Figure 1 and removable cleaning brushes;

Figure 4 is a perspective view of a cleaning assembly consisting of the apparatus of Figure 1 and removable brush scrapers;

Figure 5 is a perspective view of an assembly consisting of the apparatus of Figure 1 and flush tool elements;

Figure 6 is plan view of a recess of the apparatus of Figure 1;

Figure 7 is a cross-sectional view of an embodiment of the invention showing recess profile and an attachment arrangement for removable tool elements;

Figure 8A is a perspective view of a further embodiment of the invention having a set of recesses run in tandem;

Figure 8B is a circumferential detail of a further embodiment of the invention; and

Figure 9 is a perspective view of a further embodiment of the invention, configured as a hole opening tool.

Reference is made firstly to Figures IA, IB and 1C, in which downhole apparatus in accordance with a first embodiment of the invention is shown, generally depicted at 10. As will be described in more detail below, the downhole apparatus 10 may take the form of one of a number of different types of downhole tools or equipment. However, in general terms, the downhole apparatus 10 comprises a tubular main body 12; at least one flow channel 14 extending part-way along a length of the body 12 and a plurality of raised portions or ribs 15 formed on the body 12. The ribs 15 are shaped such that a dimension of the channel 14 (in this case, width) is non- uniform. Flow guides 16 located adjacent to an end 18 of the channel 14, the flow guide 16 and the channel 14 together defining a flow path for flow of a downhole medium along the body 12.

The apparatus 10 serves for promoting improved fluid flow along an annulus defined between the body 12 and the wall of a well borehole or of a tubing in which the apparatus is located. It will therefore be understood that the apparatus 10 may be located in open hole, that is within a drilled borehole of an oil or gas well; within tubing previously located in a borehole such as a casing or liner; or indeed within other tubing such as a tool string. The apparatus 10 therefore has a wide range of potential uses in the downhole environment.

The apparatus 10 is configured to as a tool for connection to, or incorporation into, a string of tubular members employed in wellbores . The body 12 of the apparatus 10 can be located in a wellbore with its

longitudinal axis aligned with the longitudinal axis of the wellbore.

The ribs 15 are arranged to define a specific flow path such that a channel is formed between the edges of the pads 15. The channel has varying width due to the curvature of the edges of the pads 15. The flow guides 16 may be provided with cutting edges 17A, 17B for disturbing the flow or breaking up particles and material such as debris and cuttings that may be present in the borehole fluid flow.

The ribs 15 are distributed circumferentially around the tubular body 12 with their longitudinal axes aligned with the longitudinal axis of the tubular body 12. In this embodiment three ribs are distributed with equal spacing around the circumference of the tubular body 12. The spacing and longitudinal dimension of the ribs 16 is sufficient for imparting a directional effect on fluid flowing past.

Each rib 16 is provided with longitudinally aligned recesses 11 into which different tool elements may be received and coupled to the tubular body 12. The recesses 11 comprise a substantially rectangular milled recess formed in the pad surfaces 19 of the ribs 15. In other embodiments the recesses 11 may have a different shape. The recesses are dimensioned such that a tool element located into the recess fits snugly with minimal relative motion between the tool element and the juxtaposing interior side wall surfaces of the recesses 11.

The ribs are shaped so that the basic tubular body provides the aforementioned benefits in affecting flow of fluid and cuttings, whilst providing an appropriate surface area for recesses accommodating a plurality of interchangeable tool elements. The recesses are designed to receive a plurality of different tool elements having different functions and/or different dimensions to permit the same tool body to be used in a number of different wellbore operations. In this fashion, the apparatus 10 provides the basis for a variety of tool assemblies including stabilising, reaming and cleaning tools.

Figures 2A to 2C show the apparatus of Figure 1 configured as a stabiliser assembly, for use, for example, on heavyweight drill pipe.

The assembly, generally depicted at 100, consists of the apparatus 10 and a plurality of removable tool elements, which in this example are stabiliser blades 102. The blades 102 are dimensioned to fit exactly within the longitudinal recesses 11. Attachment means are provided for removable attachment of the blades 102 to the apparatus 10.

The blades 102 are formed to a specific (radial) depth to provide stand-off between the inside wall of a wellbore and the tubular member 3. The depth, and thus the outer diameter of the assembly, is chosen according to the inner diameter of the borehole or casing in which the string is being run, in order to provide a snug fit. It will be appreciated that a variety of depths of stabiliser blades can be made available at the surface to

allow the basic apparatus 10 to be configured for a range of different borehole diameters.

Figure 3 shows the apparatus 10 configured as a cleaning tool, for use, for example, in cleaning the inner surface of casing in a wellbore. The assembly, generally depicted at 110 consists of the apparatus 10 and a plurality of removable tool elements, which in this example are wire brush assemblies 112. The brush assemblies 112 consist of brush housings 114 dimensioned to fit exactly within the longitudinal recesses 11 and an arrangement of wire bristles 116 on the exterior surface of the brush assembly. Attachment means are provided for removable attachment of the brush assemblies 112 to the apparatus 10.

It will be understood that a variety of depths of brush assemblies and bristle arrangements can be made available at the surface to allow the basic apparatus 10 to be configured for a range of different borehole diameters.

Figure 4 shows the apparatus 10 configured as part of a scraping tool, for use, for example, in scraping the inner surface of casing in a wellbore. In this embodiment, the assembly, generally depicted at 120 consists of the apparatus 10 and a plurality of removable tool elements, which in this example are brush scraper assemblies 122. The brush assemblies 122 consist of housings 124 dimensioned to fit exactly within the longitudinal recesses 11 and an arrangement of scraping bristles 126 on the exterior surface of the scraper assembly. Attachment means are provided for removable

attachment of the brush assemblies 122 to the apparatus 10.

The arrangement of Figure 4 is similar to the arrangement shown in Figure 3, although the depth of the housings is selected to be substantially flush with the ribs 15, such that only the bristles protrude from the outer surface of the ribs .

It will be understood that a number of different tool elements having scraper blades, bristles or pads could be provided for a variety of cleaning operations.

Figure 5 shows the apparatus 10 in an alternative configuration, generally depicted at 130, in which the recesses 11 are provided with inserts flush to the outer surface of the ribs 15. In this embodiment, the tool may be run in wellbore of diameter substantially equal to the outer diameter of the ribs 15 and the flow guides 16 and perform a number of different stabilising, centralising, reaming, cleaning or scraping functions.

The arrangement of the leading set of flow guides 16, the various channels 14 defined by the ribs 15, and the trailing set of flow guides 16 define a number of flow paths for flow of fluid across the main body 12 of the apparatus 10. These various flow paths provide an efficient mixing of constituents of the downhole medium, preventing blockage of the flow paths and in particular of the channels 14, in use.

The apparatus 10 additionally defines a number of cutting or abrading surfaces, for reaming a borehole, or for

cleaning an inner surface of tubing in which the apparatus is located. In more detail, the end of each flow guide 16 typically forms a relatively aggressive cleaning blade or scraper for reaming/cleaning during passage of the apparatus downhole. In a similar fashion, the end of each trailing flow guide 16 defines less aggressive blades or scrapers, to provide a reaming/cleaning function when the apparatus is translated uphole. Also, each of the ends of the guides 16 and the edges of the ribs 15 may define blades or scrapers, for providing a rotary reaming/cleaning function. Furthermore, radially outer surfaces of the apparatus 10, such as outer surfaces of the ribs 15 and guides 16 may define or include abrasive particles, and may, for example, be coated with Tungsten-Carbide grit.

Particular applications for which flush inserts are provided include applications when the apparatus is used as a sleeve or housing for a downhole tool such as a downhole motor, and serves to centralise or support the tool within a bore hole or existing tubing.

Flush inserts may also be used where the apparatus forms part of a casing shoe or a drill shoe. The apparatus may for example for part of a casing shoe reamer which assists the passage of a casing string into a drilled wellbore.

There now follows a description of the details of the attachment between the main body of the apparatus and the tool elements.

Figure 6 is a plan view of a recess 11 formed in a rib 15 on a tubular body 12. Figure 7 shows a cross section through a different tubular body 12 ' having three recesses 11' formed therein. Although the embodiment of Figure 3 lacks the ribs of the embodiment of Figure 2, the shape and form of the recesses 11' and the attachment means are identical to recesses 11.

The recesses 11, 11' comprise a base surface having a first portion 21 formed to a specified depth below the outer surface of the body 12. The first portion 21 extends along the entire length of the longitudinal recesses 11, 11', and the surface of the first portion lies in a plane substantially aligned perpendicular to the normal axis of the body 12. That is, the first portion 21 forms the base of a square section recess.

The recesses 11, 11' also comprise a second portion 22 extending along the entire length of the longitudinal recess 11, and forming the junction between the first portion 21 and a side wall 24 of the recess. The surface of the second portion lies in a plane inclined with respect to the first portion 21 and the side wall 24, and the second portion 22 therefore forms a surface inclined to the normal axis of the body.

The first and second portions 21, 22 of the base surface are provided with threaded bores 31, 32 and 33 for receiving screws for attachment of tool elements. Bores 31 are provided in the first portion 21 along a central longitudinal axis of the recess. The bores 31 are substantially radially aligned, to receive a screw

aligned on the normal axis of the main body 12, through a corresponding bore in the removable tool element .

Bores 33 are provided close to the corners of the recess 11, and are similarly radially aligned to receive screws aligned on the normal axis of the main body 12, through corresponding bores in the tool elements . This attachment arrangement is suitable for attaching, for example, the brush assemblies as shown in Figure 3.

Bores 32 are provided in the second portion 22, and are aligned normally to the inclined surface of the second portion, as most clearly shown in Figure 6.

In the arrangement of Figure 6, tool elements 34 have a cross-sectional profile to fit with the cross-sectional profile of the recess 11'. In this example, one edge of the tool element 34 is provided with a shoulder 35 which abuts the outer surface of the body 12 ' along the edge of the recess 11' .

The tool element 34 has a prismatic profile that is formed to fit closely into the recess 11'. The depth of the pocket 11 and thickness of the tool element is sufficient that displacement by tangential or longitudinal forces is limited or avoided.

The tool elements 34 are secured to the tubular body 12' by means of screws (not shown) that are provided through a securing bore 36 in the tool element 34. The bore 36 extends from a scalloped opening 38 provided in an edge 39 of the tool element 34. The holes 36 align with threaded holes 32 in the body 12' in the angular surface

22 of the recess 11'. The threaded holes 32 engage and secure to a mating thread at the end of the screw. The head of the screw abuts against an abutting surface in the opening 38.

In this embodiment, the positioning of the bore opening 38 and the screw head at a side of the tool element 34 prevents interference with the operational part of the tool element. Further, the attachment arrangement is such that upon clockwise rotation of the tool in the wellbore, forces imparted on the tool element 34 by the wellbore walls will tend to be directed axially along the longitudinal axis of the screws and will therefore tend to prevent the screw from being subjected to non co-axial stresses and strains.

The attachment arrangement of Figure 7 provides additional advantages in relation to tool elements with a large depth or radial dimension, such as stabiliser blades. If a stabiliser blade is required to give 6" (15cm) stand-off between a wellbore wall and the main body of the tool, a screw normally aligned through the tool element may be required to be up to 12" (30cm) so that it can extend through the full depth of the stabiliser blade and into the body 12'. By providing an inclined bore and screw, the length of the blade can be reduced. In addition, the same length of screw could be used for all sizes of stabiliser blade.

The apparatus also provides threaded bores 31, 33 (not shown in Figure 7 for clarity reasons) for attachment of other tool elements with different locations of securing holes. For example, threaded bores 33 may be used in an

alternative embodiment where the tool elements to be located in the recesses 11, 11' have securing holes in corresponding corners. This functionality provides for attaching tools by the method most suited to their performance .

It will be appreciated that the attachment arrangement of Figure 7 may be applied to other recess and tool element configurations in addition to any of the embodiments described hereto. It will also be appreciated that although the described embodiments have an inclined bore 32 at approximately 45 degrees to the normal axis of the body 12, other angles of inclination may be used. Additionally, in alternative embodiments the inclined surface profile may differ, and include additional portions with different angles of inclination, or indeed curved portions. Although it is preferred that the surface profile includes at least one angled or curved portion, it is not an essential part of the invention. It will be understood that an inclined axis for the attachment means provides the benefits and advantages described above.

Figures 8A and 8B show a further embodiment of the invention configured as a magnetic junk recovery tool, generally depicted at 140. In this embodiment, the tool comprises a tubular body having male and female rotary shouldered connection 142a and 142b at first and second ends respectively. In this embodiment, the tool comprises two sets of ribs 15a and 15b, having respectively two sets of recesses 11a and lib. One set of hex pads 144 are located in between sets of ribs and recesses. The tool 140 can therefore be considered as a

pair of tools 10 of Figure 1 run in tandem. As before, the tool is provided with leading and trailing flow guide 146.

As in the embodiment of Figure 1, each set of ribs 15 comprises three ribs circumferentially displaced at 120 degrees. However, the blades 15b are rotationally off- set with respect to blades 15a by 60 degrees. This causes the ribs 15b to be aligned with the flow path defined by ribs 15a. The provision of the two sets of recesses rotationally off-set provides maximum circumferential coverage when running the tool in the wellbore.

The recesses 11a and lib are provided with magnetic inserts 148. These magnetic inserts are countersunk into the recesses to provide a pocket for containing ferrous debris, junk and cuttings from the wellbore.

A variety of magnetic inserts could be used. For example, the recess could be provided with a metallic plate, which on its lower side is provided with recesses to accommodate a number of magnets to be retained beneath the plate.

In the embodiments shown, the ribs 15 are formed to the same height as the flow guides 146, which are gauge with the casing in which the tool is run. However, in alternative embodiments, the radial height of the ribs 15 could be lower than that of the flow guides 146. This may improve the ability of the tool to collect debris and junk from the wellbore.

It will be appreciated that the tandem design shown in Figures 8A and 8B could be adopted for alternative operational configurations. For example, the cleaning tools of Figures 3 and 4 could comprise a tandem configuration, with one set of cleaning tool elements rotationally off-set with respect to the other. This would provide increased circumferential coverage of the cleaning tool when being run in the wellbore.

It should be noted that Figure 8B is a circumferential view of a tool configuration very similar to that of Figure 8A, although the shape of the intermediate pads 144' is different.

Figure 9 illustrates a further embodiment of the invention, in which the tool body of Figure 1 receives a hole opener tool element 152 to provide a hole opener tool, generally shown at 150.

The hole opening tool element comprises a support member 152 shaped to be received in the recess 11, and which extends radially from the tool body. The support member 152 is provided with a leading face 154 which is inclined towards the tubular body. The face 154 provides a bearing surface for a rotary cutter blade 156, which is mounted rotationally via a bore 158 extending through the support member 152. When assembled, the rotary cutter member 156 is aligned in the space defined by the flow guide members 16. The rotary cutting member 156 does not contact the tubular body, and is free to rotate about the axis defined by the bore 158. When assembled, the hole opener tool consists of three support members 152 and cutting members 156, one for each of the recesses 11.

The tool 150 may be part of kit of parts comprising a plurality of tool elements including hole opener tool elements. Hole opener tool elements of different radial dimensions may be provided, such that tool elements are available to increase the diameter of a well bore to a specific size. The tool may also be configured in tandem, such that a hole opener tool of a first bit size, for example 17% inches (445 millimetres) is provided below a second hole opener tool having bit size of 26 inches (660 millimetres).

In this embodiment, the tool is also provided with jetting port 160 located in the outer surface of the flow guide 16. The jetting port provides a flow path from the internal bore of the tool to the exterior of the tool. The jetting port 160 is configured to direct a fluid towards the rotary cutters 156 to remove cuttings from the cutting blades .

It should be appreciated that tool elements for carrying out operations other than those described above could also be employed by attaching them into pockets in a manner similar to the tool elements of the previously described embodiments. For example, the recess may receive a roller reamer tool element.

It will be understood that in certain embodiments, the shape and configuration of the ribs may vary. For example, the ribs may be helically oriented.

The multi-functional downhole tool as described in the above embodiments provides a number of advantages. The

ribs 15 allow brushes, scrapers, blades or other tool elements to be attached and engage with the wellbore over the length of the ribs. Tool elements with relatively large surface and operational area may therefore be employed whilst fluid flow is spatially well- accommodated.

In addition, the provision of ribs 15 to create a channel 15 in the tool portion 5 and perturbations imparted on the fluid flow improves the efficiency of removing material and flow fluid away from and past the downhole tool during operation, particularly in a mode of operation where the tool is run with minimal stand-off. Further, flow guides 16 assist in the above flow by breaking down globules of particles or other material that may be present in the fluid.

Another advantage is that the tool minimises costs arising from operational wear as it is only necessary to change out and replace the particular elements that are worn. Further, the simple attachment arrangement promotes easy handling and replacement in the field and is relatively quick to replace. Furthermore, the flexibility of using a generic tubular member can reduce the initial capital expenditure that would otherwise be required when using separate tools for different purposes.

The present invention provides an improved system for performing a number of downhole functions whilst efficiently removing borehole fluid, particles and debris from a well bore.

In use, the multi-functional downhole tool is typically attached as part of a drill string upon which torque is imparted during drilling of a well. The tool allows removable attachment of different tool elements for performing various functions during rotary drilling and upon insertion and extraction of the drill string from the well . Tool elements such as brushes or scrapers or wipers are screwed into pockets provided in pads located on the downhole tool by securing them to. This may be necessary for commencing new operations or to replace worn tool elements.

Whilst the string containing the tool is located in the well bore, functions such as cleaning, scraping or stabilising of the wellbore may be carried out whilst rotary drilling is taking place. As drilling is progressing, drill fluid is pumped through the central annulus of the tool string and returned up through the annulus of the wellbore created between the string and the wellbore wall. Flow guides and tool elements provided on the tubular channel the flow of fluid up through the annular space. The flow guides help to break up material located in the flow preventing the tools from clogging and enhancing performance.

Various modifications and improvements may be made within the scope of the invention herein described.