The present invention relates to a cleaning apparatus for cleaning the inner surface of a well bore tubular, and to a method of cleaning a well bore tubular.

Earlier designs of cleaning apparatus such as are shown in GB2499953A,

US7878238 and US5711046 (incorporated herein by reference) incorporate cleaning devices such as pads and scrapers on the outer surface of tubular bodies, and stabilisers.

According to the present invention there is provided apparatus for cleaning the inner surface of a well bore tubular, the apparatus comprising:

a body having an axis and an axial bore through the body, suitable for connection into a tool string for use in a well bore tubular,

and a cleaning device on the outer surface of the body for engaging the inner surface of the well bore tubular,

wherein the cleaning device comprises a cleaning member in the form of an elongate strip having a head retained in a slot.

Optionally the slot is formed on the cleaning device, which is optionally in the form of a pad retained on the outer surface of the body. Optionally the cleaning device (e.g. the pad) is removable from the body. Optionally the pad is supported by at least one resilient device such as a spring, optionally in the manner disclosed in US7878238, US5711046 and GB2499953A, the disclosures of which are

incorporated herein by reference. The pad can optionally be retained in a recess in the manner described in US7878238, US5711046 and GB2499953A, optionally by a collar on the body that extends over a lip on the pad. Optionally the slot is formed in the radially outermost surface of the pad, facing the radially innermost surface of the well bore tubular. Optionally more than one slot is formed on the outer surface of the pad, each slot optionally retaining the head of at least one elongate cleaning member. Optionally more than one slot is provided in the pad, and where this is the case, the slots on each pad are optionally parallel to one another. Optionally the slot is angled with respect to the axis of the body. In certain examples, the slot can extend helically with respect to the axis of the body. Optionally the pad has a helical array of mutually parallel slots on its outer surface. The pitch of the helix can be adjusted in different examples of the invention.

Optionally the slots can be spaced from one another on the pad, optionally axially spaced from one another with respect to the axis of the body. Optionally, a channel can be formed between the cleaning members disposed within adjacent slots.

Optionally the channel can be wider than the slots. Optionally the

channels are parallel to the slots. Optionally, the channels provide a conduit (optionally helical) in the annulus between the body and the inner surface of the wellbore for flow of fluid and particulate materials, washed from the inner surface of the wellbore.

Optionally, in certain examples of the invention with helical slots, the slots and the channels can extend in the same helical direction as the direction of intended rotation of the body in use. In most examples of the invention, the body will be rotated clockwise around the axis of the bore when viewed from the perspective above the string, and hence the helical direction of the slots and the channels is optionally a clockwise direction. However, in certain examples, intended for clockwise rotation in a conventional string, the helical direction of the slot and the channels can be opposite to the intended rotational direction of the string, i.e.

anticlockwise. Different effects can be achieved by this modification, including presenting a generally flat brush or scraper surface to the wellbore with the anticlockwise helical direction examples, as opposed to a relatively narrower brush or scraper surface presented by the "edge-on" clockwise helical direction examples. Of course, certain examples of the invention can be contemplated for use in unconventional well is where the direction of rotation from the surface is not clockwise but anticlockwise, and either clockwise or anticlockwise helical directions of the slots and channels can be employed in those examples, in a similar way as described above.

In certain examples of the invention, the slots can extend parallel to the axis of the body, i.e. between the axial ends of the pads, without circumferential deviation, i.e. without any helical arrangements.

Optionally the cross-sectional profile of the slot can include a neck at a radially outer part of the slot that is narrower than the head of the cleaning member, and optionally narrower than a radially inner base of the slot. Optionally, the neck of the slot retains the relatively larger head of the cleaning member within the radially inner base of the slot, and prevents the escape of the head from the slot in a radial direction. The head of the cleaning member is optionally the same shape in cross- section as the cross-sectional shape of the slot, with a neck that is relatively narrower than the head of the cleaning member. Optional cross-sectional shapes for the head of the cleaning member and the slot include L-shapes, T-shapes, dovetails, tear drops and the like. The principal requirement is that the head of the cleaning member is retained within the slot by the neck of the slot. Optionally the slot has at least one open end, optionally at one lateral edge of the pad, and the cleaning member is optionally engaged within the slot by offering the head of the cleaning member to the open end of the slot, and sliding the head of the elongate cleaning member along the slot, so that the neck of the slot encloses the head of the cleaning member, thereby retaining the cleaning member within the slot, and resisting pull-out of the head from the slot. The cleaning member is therefore optionally slidably engaged within the slot.

Optionally, each slot can have more than one open end, through which the head of the cleaning member is slid during insertion of the cleaning member into the slot. Optionally, the open end(s) of the slot(s) can be closed in the assembled tool by portions of the body abutting against the open ends, to resist sliding of the elongate cleaning member head out of position in the slot during use of the tool. Optionally, the apparatus can include a stabiliser arranged on the outer surface of the body, and optionally a junk basket as described in GB2499953A, the disclosure of is incorporated herein by reference.

Optionally the cleaning members present a cleaning surface radially outwardly from the cleaning members. Optionally the cleaning members incorporate brushes. Optionally the cleaning members can incorporate blades. Optionally the cleaning devices are arranged in aligned rows, and optionally pads incorporating cleaning devices are circumferentially staggered so as to cover substantially the whole of the circumference of the body with cleaning surfaces, although there may be axial spacing between different pads.

Optionally the cleaning devices are mounted on resilient devices such as springs that are held in compression against the body, so as to urge the cleaning devices radially outward against the inner surface of the well bore tubular being cleaned. Optionally the body of the cleaning pads on which the brushes or scrapers etc. are mounted has a smaller outer diameter than the outer diameter of the blades on the stabilisers, so that even when the cleaning devices are urged outward to the maximum extent by the springs compressed between the cleaning device and the body, the body of the cleaning device does not engage the inner surface of the wellbore directly, but instead presses the cleaning formations such as the brushes and scrapers held on the outer surface of the body of the cleaning device against the inner surface of the wellbore tubular being cleaned. This reduces wear on body of the cleaning devices, which is spaced from the inner surface of the tubular by the stabiliser.

Optionally the cleaning devices are fixed to the body of the sub in recesses formed in the outer surface of the sub, and are optionally unable to rotate relative to the body. Accordingly, torque and axial thrust applied to the body of the sub is optionally transmitted efficiently to the cleaning devices, which scrape and/or brush against the inner surface of the wellbore tubular being cleaned, removing debris. Optionally, the cleaning devices (i.e. pads) are removable from the body, allowing replacement of the cleaning devices when they are worn. Optionally the cleaning devices are restrained against radial movement by restrainers such as annular rings which optionally extend over a portion of each cleaning pad, allowing limited radial movement to compress the springs inwardly, but limiting outward radial movement of the cleaning devices beyond the extent permitted by the annular rings. Optionally the annular rings, or some of them, are secured to the body by screw threads for example on the outer surface of the body, allowing removal of the annular rings when the cleaning devices are to be removed for maintenance or replacement. The pads are optionally formed with lips to engage a counter bore of the retaining rings, which optionally allows the pads a range of free radial movement within the limits of the counter bore while under compression in the tubular. The resilient springs press the pads against the inner wall of the tubular during cleaning operations, and at the same time compensate for radial dimensional changes due to wear of the brushes or scraper formations. Optionally, the rings retaining the pads on the body can be screwed on in opposite hands relative to one another, facilitating the relative tightening of the two rings. Optionally, backing off of the rings on the thread can be restricted by a resilient device such as a spring.

Optionally the incorporation of the apparatus in a work string can reduce the number of tools currently used in the string, reducing the length, cost and complexity of the string. Optionally the same tool body can be used for a scraper or a brush tool by replacing the cleaning devices and/or the cleaning members. Optionally some of the cleaning devices (e.g. the pads) can incorporate scrapers, and some can incorporate brushes, at either the same or different axially spaced recesses on the same body. Optionally, the cleaning members are formed by elongate metallic members, which are folded, e.g. in half at a central portion, and wherein the central portion is then retained within a channel member which is deformed around the fold of the central portion of the elongate metallic member by crimping, pressing, or swaging or the like, to retain the folded central portion of the elongate metallic member. Optionally, the central portion of the elongate member is pressed into the channel member using a retaining member, which remains within the channel of the channel member as the channel member is being deformed around the central portion of the elongate member. Optionally the elongate metallic members are resilient. Optionally the cleaning members thereby have more than one leaf.

Optionally, the cleaning members can be brushes, formed from elongate metallic members in the form of bristles, optionally made from wire, optionally steel wire such a stainless steel.

Optionally, the cleaning members can be blades formed from elongate metallic members in the form of metal strips, which may comprise steel, for example stainless steel.

Optionally the slots can receive scrapers, comprising a head and blade. The head can be formed by a channel which retains a central portion of the blade. Optionally the blade can be formed from a sheet, optionally resilient material, and optionally a metal, for example spring steel sheet. Optionally, the blade can have more than one leaf, each leaf being arranged parallel to adjacent leaves on the blade, and optionally stacked in layers. Optionally the blade can be formed by inserting a retaining rod into a channel and retaining a central part of a strip within the channel, optionally by crimping the channel walls together after insertion of the rod into the channel.

The various aspects of the present invention can be practiced alone or in

combination with one or more of the other aspects, as will be appreciated by those skilled in the relevant arts. The various aspects of the invention can optionally be provided in combination with one or more of the optional features of the other aspects of the invention. Also, optional features described in relation to one example can optionally be combined alone or together with other features in different examples of the invention. Any subject matter described in the specification can be combined with any other subject matter in the specification to form a novel combination.

Various examples and aspects of the invention will now be described in detail with reference to the accompanying figures. Still other aspects, features, and advantages of the present invention are readily apparent from the entire description thereof, including the figures, which illustrate a number of exemplary aspects and implementations. The invention is also capable of other and different aspects and implementations, and its several details can be modified in various respects, all without departing from the present invention. Accordingly, the drawings and descriptions are to be regarded as illustrative in nature, and not as restrictive. Furthermore, the terminology and phraseology used herein is solely used for descriptive purposes and should not be construed as limiting in scope. Language such as "including," "comprising," "having," "containing," or "involving," and variations thereof, is intended to be broad and encompass the subject matter listed thereafter, equivalents, and additional subject matter not recited, and is not intended to exclude other additives, components, integers or steps. Likewise, the term "comprising" is considered synonymous with the terms "including" or "containing" for applicable legal purposes.

Any discussion of documents, acts, materials, devices, articles and the like is included in the specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention.

In this disclosure, whenever a composition, an element or a group of elements is preceded with the transitional phrase "comprising", it is understood that we also contemplate the same composition, element or group of elements with transitional phrases "consisting essentially of", "consisting", "selected from the group of consisting of", "including", or "is" preceding the recitation of the composition, element or group of elements and vice versa. All numerical values in this disclosure are understood as being modified by "about". All singular forms of elements, or any other components described herein are understood to include plural forms thereof and vice versa. References to positional descriptions such as upper and lower and directions such as "up", "down" etc. in relation to the well are to be interpreted by a skilled reader in the context of the examples described and are not to be interpreted as limiting the invention to the literal interpretation of the term, but instead should be as understood by the skilled addressee, particularly noting that "up" with reference to a well refers to a direction towards the surface, and "down" refers to a direction deeper into the well, and includes the typical situation where a rig is above a wellhead, and the well extends down from the wellhead into the formation, but also horizontal wells where the formation may not necessarily be below the wellhead. In the accompanying drawings,

Figure 1 is a side view of a sub;

Figure 2 shows a longitudinal section view through the figure 1 sub;

Figure 3 shows a section view through the sub of figure 1 through a cleaning pad;

Figure 4 shows a plan view of a cleaning pad in the sub of figure 1;

Figure 5 shows a side sectional view through the line CC in figure 4;

Figure 6 shows an end elevation on DD of figure 4;

Figure 7 shows an enlarged view of a portion of figure 5;

Figure 8 shows a plan view of a body of the pad shown in figure 4;

Figure 9 shows a side sectional view through the line AA in figure 7;

Figure 10 shows an end elevation on BB in figure 8;

Figure 11 shows an enlarged view of a portion of figure 9;

Figure 12 is a cross sectional view of a head of a cleaning member used in Figure 4; Figure 13 shows a plan view of a 2nd example of a cleaning pad, for use in the sub of figure 1;

Figure 14 shows a side sectional view through the line AA in figure 13;

Figure 15 shows an end elevation on BB of figure 13;

Figure 16 shows an enlarged view of a portion of figure 14; Figure 17 and 18 each show a side sectional view of sequential positions in the formation of a blade suitable for use in the cleaning pad of figure 13;

Figure 19 shows a plan view of a further example of a blade suitable for use in the cleaning pad of figure 13;

Figures 20 and 21 show side sectional views of alternative configurations of cleaning device suitable for use in any of the presently described examples of the invention.

Referring now to the drawings, a sub 1 is shown suitable for incorporation into a work or drill string for deployment in an oil or gas well, and has, for this purpose, box and pin connections at opposite ends. Typically the box connection is provided at its upper end, which in this case is shown on the right hand side of figure 1, and the pin connection is provided at its lower end, at the left-hand side of figure 1. The skilled person will appreciate that different connections can be used, and the terms upper and lower, and similar terms reflecting the orientation of the sub in a wellbore, are used to indicate distance along the wellbore between each component being discussed and the wellhead at the surface of the well, and that in practice, in certain deviated and horizontal well bores, a component that is referred to as an "upper" portion may actually be deeper underground than a different portion that is referred to as a "lower" portion. The drill string in which the sub 1 is connected is typically rotated during rotary drilling operations in a clockwise direction as viewed from above.

The sub 1 comprises a generally tubular body 10 having a central bore 10b extending through the sub 1. Optionally, one or both of the ends may be provided with a fishing neck, or other formation to enable manipulation and/or retrieval of the sub 1 from a wellbore in the event of intervention operations being required.

The upper end portion of the body 10 has, adjacent the box connection, a larger diameter than the lower end portion, and consequently the generally tubular components that are applied to the outer surface of the body 10 as the sub 1 is constructed each comprise a central bore which is offered to the body 10 as each component is passed over the relatively narrower lower end. The sub 1 has a lower stabiliser assembly 2, a central cleaning device assembly 3, and an upper stabiliser assembly 4, which are all assembled around the outer surface of the body 10, optionally with the upper stabiliser assembly and associated components being offered first to the lower end of the body, followed by

components of the cleaning device assembly 3, followed by components of the lower stabiliser assembly 2. Optionally more than two stabiliser assemblies can be provided. The stabilisers are optionally axially spaced from one another along the sub 1. Optionally all the components are incorporated on the same sub 1.

The central cleaning device assembly 3 optionally comprises a number of cleaning devices in the form of cleaning pads 31 housed in recesses in the body 10 (best seen in the section view of figure 3). The recesses housing the pads 31 prevent lateral movement of the pads 31 in the recesses as the string rotates. The pads 31 are restrained against axial movement within the recesses as the string advances axially into the well by a central pad retaining ring, which is welded or otherwise secured onto the outer surface of the body 10, and by upper and lower pad retaining rings 33u, 331. The pad retaining rings 33 define the upper and lower axial boundaries of the recesses housing the pads 31, so that when the rings are in place, the pads are secured against axial and lateral movement within the recesses. The rings 33 also optionally have an internal undercut to restrain radial movement of the pads 31(with respect to the axis of the body) within the recesses. Resilient devices such as springs are optionally provided between the pads 31 and the body 10, and are optionally held in compression, which serves to urge the pads radially outwards from the axis of the body 10, until the outer faces of the lips on each of the pads 31 engage the inner surfaces of the undercut formed on the rings, which will limit the radial extension of their pads 31 out of the recesses. Accordingly, the pads 31 are restrained within the recesses on the body by the interaction of the recesses and the pad retaining rings so that the pads 31 are urged radially outward to the furthest extent under the force of the radially compressed springs, and limited inward radial movement of each pad 31 is permitted, when the force applied to the pad 31 exceeds the force of the springs. In that event, when the pad 31 is urged radially inward, for example if the tool is lying on the low side of a deviated well bore, and the full weight of the sub 1 is bearing down on one of the pads 31, then the springs supporting that particular pad 31 will tend to be compressed, allowing the pad 31 to move radially inwards, into the recess, but the boundaries of the recess, and the pad retaining rings 33, will restrict lateral and axial movement of the pads 31.

The upper and lower pad retaining rings optionally act as nuts provided with an internal screw thread on an area of the internal diameter that is spaced from the undercut, allowing the screw thread to cooperate with an external screw thread on the body 10. Optionally the upper and lower rings have opposite hands of screw thread, to facilitate tightening of the rings to secure the pads. Accordingly, the pad retaining rings 33 can be moved axially along the outer surface of the body 10 by means of the cooperating screw threads, to secure and release the lips on the pads 31. When the pads 31 are to be replaced, the pad retaining rings 33 can be backed off from the recess by means of the screw threads, to permit the pads 31 to be removed from the body 10. Alternatively, the rings 33 can be unthreaded, and can be held in place themselves by threaded bushes 33b. Other mechanisms can be used to hold the rings in place, for example, the ring or a bushing can be held in place by a circlip engaged in a recess in the outer surface of the body.

Optionally the central pad retaining ring 32 is formed as two half shells which can optionally be welded or bolted or otherwise attached to the central part of the recess in the body 10, optionally after the upper stabiliser assembly 4 and the upper pad retaining ring have been applied to the body and moved into their respective places.

Optionally at least one of the upper and lower pad retaining rings 33 is urged by a strong spring surrounding the body and held in compression between, for example, the upper pad retaining ring 33u and the upper stabiliser assembly 4, to resist backing off of the rings 33 on their threads. Likewise, a similar spring can be held in compression between the lower pad retaining ring 331 and the lower stabiliser assembly 2. Alternatively the springs can urge the threaded bushes 33b.

Alternatively, the rings 33 and/or bushes 33b can be held in place by circlips.

Referring now to figures 4 to 12, one example of a cleaning device in the form of a pad for use in the sub 1 is disclosed. The cleaning pad is generally rectangular in plan view, but has an arcuate cross-section with an arcuate outer surface as best shown in figure 6 and figure 10, to match the curvature of the outer surface of the sub, and optionally to match the curvature of the inner surface of the wellbore, in which the sub 1 is deployed. Matching the curvature between the wellbore and the pad is beneficial, as it promotes more even wear on the pad and on the tubular being cleaned, and enhances the cleaning effect on the inner surface of the wellbore.

The pad has a body 35, having an axially extending lip 36 at each axial end, which is advantageously milled from the outer surface, and having a plurality of slots 37 for receiving cleaning members. The slots 37 are cut into the outer surface of central section of the body 35 between the lips 36 at each end. The central section of the body 35 between the lips 36 at each end has a plateau region with a larger outer diameter, and two end ramps leading to the lips 36. The cleaning members in this example are brushes 38, best shown in figure 7. The slots 37 on the central section extend from one side of the pad to the other, are optionally parallel to one another, and optionally extend both circumferentially around the outer surface of the pad, and axially between the ends of the pad, so that each slot 37 follows a portion of a helical path around the outer surface of the central section of the pad 31. The side walls of each slot 37 extend from an opening in the radially outermost surface of the pad 31 in a generally radial direction with respect to the axis of the sub 1, terminating in a base of the slot 37. However, the walls of the slot 37 are non- parallel and diverge as the slot extends radially inward toward the axis of the sub 1. Hence, the neck of each slot 37 is narrower than the base, so that each slot 37 has a dovetail profile when viewed in cross-section, as best seen in figure 9. In each case, the neck of each slot 37 is approximately 10 to 70% of the width of the base, optionally 50-60% but the particular dimensions of each slot 37 can vary in accordance with its depth, the angle of its side walls and its desired specification. The dovetail profile of each slot 37 retains the head 38h of a brush 38, which optionally has a matching dovetail profile, when viewed in cross-section, as best seen in figure 7. While some examples can be constructed without matching profiles between the head of the cleaning member and the slot, matching these profiles secures the head of the cleaning member better within the slot 37.

The lateral ends of the slots 37 are open at the side edges of each pad, and the brushes 38 are inserted into the pads before use by sliding the head 38h of a brush 38 into a respective slot. Optionally, each slot 37 receives at least one brush 38, but it is possible for each slot 37 to receive more than one brush 38, and it is not necessary for each slot on the pad to receive a brush 38. Optionally, the head of a brush 38 is offered to the slot 37 before the pad is assembled onto the cleaning device and made up into the sub. Optionally the operator slides each brush head 38h along the slot 37 until the ends of the brush 38 reach the open side edges of the slot, thereby filling each slot 37 with at least one brush 38 before attaching the pad onto the cleaning device. When the assembled pad, bearing the cleaning members, is received within the recess on the body, the pad retaining rings at the upper and lower axial ends of the pad restrain the pad within the recess, so that the open side edges of the slots 37 extend into the recess below the surface of the body, which closes the open side edges of the slots 37, and prevents lateral movement of the cleaning members within the slots. Since the cleaning members cannot escape laterally from the slots 37 when assembled, and since they are retained against radial movement by the dovetail shape of the slot, they are secured against movement relative to the pad as the tool moves within the borehole.

The inner surface of each pad has a number of (for example 4) radial pockets 34 in the form of blind ended bores facing radially inwards for receiving springs or other resilient devices, which are held in compression between the inner surface of the pad and outer surface of the recess on the body, acting to push the pad radially outward from the recess on the body, within the limitations of movement imposed by the pad retaining rings at the upper and lower ends of each pad. The helical pattern of the slots 37 on each pad can be at different pitches of helix, but in some examples of the invention, the width of the pad, and the length of the slot 37 is chosen in combination with the pitch of the helix, so that each slot 37 overlaps in an axial direction along the pad with adjacent slots 37. In other words, the end of one slot 37 overlaps axially with the beginning of an adjacent slot. This pattern is optionally repeated along the pad, so that there are no spaces in the coverage of the brushes 38 or other cleaning members along the axial direction of the pad, and so the brushes 38 extend over substantially the whole axial surface of the pad. In other words, when viewed from the side, the whole length of the pad is covered with brushes because of the overlap. This is useful optional feature, because when the sub 1 is rotating at a fixed axial position without axial penetration of the wellbore, the whole circumference of the inner surface of the wellbore is claimed by each pad, even without axial penetration of the sub 1.

In this example, the pads are also circumferentially and axially offset from one another, and optionally overlap around the circumference of the sub 1, so that the whole circumference of the sub 1 is covered with the cleaning members extending from the combined areas of the pads. Also, when viewed from above or below, the whole circumference of each pad is covered with brushes because of the extension of the slots from one side of the pad to the other, and because the brushes fill the slots. This is another useful optional feature, because when the sub 1 is penetrating axially in the wellbore without rotating, there are no circumferential gaps in the coverage of cleaning members around the circumference of the sub, thereby allowing the sub 1 to be axially reciprocated without necessarily being rotated, and still achieve complete circumferential cleaning of the wellbore. Optionally the circumferential and axial offset between means that at least one pad is located circumferentially at each point on the circumference of the body. Optionally the bristles formed on the brushes comprise resilient wires of stainless steel, which are optionally formed in lengths that are roughly twice the distance between the desired radial outer edge of the brush 38, and the tip of the head 38h. The brushes 38 are optionally formed by arranging the wires in elongate bundles along the length of a generally U-shaped channel 38c which will form the head of the cleaning member, and pressing the central portion of each wire into the U-shaped channel 38c with a retaining bar above them. The retaining bar can optionally be a round bar, but can have different shapes of cross-section in other examples. The retaining bar is pressed the down into the U-shaped channel 38c on top of the central portion of the wires as far as possible, and then the U-shaped channel 38c is crimped at the top in a press so as to close the neck of the U-shaped channel 38c around the protruding wires. The closure of the neck prevents the escape of the bar from the crimped U-shaped channel 38c, and the arrangement of wires is therefore trapped in its double folded configuration within the channel 38c. Figure 12 shows a cross-sectional schematic arrangement of an optional brush head 38 formed by this manner. The lateral ends of each head are closed by crimping, or pressing, or swaging the walls of the channel 38c from an initial position in which the walls of the channel are parallel, to the position shown in figure 12, in which the upper ends of the walls of the channel 38c are pressed together, so that no lateral movement of the wires or the bar is permitted with respect to the channel 38c. Optionally, the channel 38c can be filled with adhesive, or other filler which helps to pack the space within the channel 38c, and enable it to resist compressive forces more easily, but this is not necessary in some examples. Optionally the brush heads 38h are formed in sections that are similar in length to the slots 37, so that one slot 37 optionally accommodates a single cleaning member, which extends from one end of the slot 37 to the other. Filling the slots 37 with a single cleaning member in this manner reduces the extent of lateral movement of the cleaning member within the slot when the sub 1 is in use, and is therefore an advantage.

The sub 1 is typically used in aggressive environments, which wear down the cleaning members during normal use. One significant advantage of making the cleaning members slidably removable from the pads is that as the cleaning members wear down, they can be replaced simply by sliding the worn cleaning members laterally out of the slots as the pads are removed for redressing the tool, and replacing them with new cleaning members. Typically the pads will see uneven wear patterns, with more wear at the leading end of the pad than at the trailing end. Accordingly, in examples of the invention, the first few rows of cleaning members in a particular pad can be replaced when the pad is redressed without necessarily replacing the cleaning members in other rows. Also, since it is relatively easy to replace the cleaning members in the pad when the tools recovered to the surface, the cleaning members can be replaced more often, before they wear down to such an extent that the inner surface of the wellbore being cleaned bears onto the pad rather than the brush. This is an advantage, because wear on the body of the pad can be substantially reduced, or even obviated entirely, allowing the body of the pad to be reused by replacing the worn cleaning members as often as required.

Optionally the body of each cleaning pad 31 has a smaller outer diameter than the outer diameter of the stabilisers (optionally smaller than the blades on the stabilisers) as best seen in figure 1, so that even when the pads 31 are urged outward to the maximum extent by the springs compressed between the pads 31 and the body 10, the body of the pads 31 does not engage the inner surface of the wellbore directly, but instead presses the cleaning members on the outer surface of the pads 31 against the inner surface of the wellbore tubular, so that the surface is cleaned by the pads 31, as seen in figure 1. This minimum standoff reduces wear on body of the pads 31.

The lower stabiliser assembly 2 comprises a tubular stabiliser optionally having two axially spaced apart arrays of blades projecting radially from the outer surface of the stabiliser, essentially as described in GB2499953A and the reader is referred to the description of the stabiliser assemblies therein for the details.

At the upper end, an upper stabiliser assembly optionally incorporates an integral junk catcher 5 essentially as described in GB2499953A and the reader is referred to the description of the stabiliser assemblies therein for the details.

In use, the sub 1 is connected into a tool string or work string which may optionally incorporate other cleaning tools or tools that have other functions, and deployed in a wellbore lined with casing C to be cleaned. Typically well bores to be cleaned might include production tubing, casing, liner, or other kinds of well bore tubing. Typically the inner diameter of the wellbore tubing to be cleaned is known, and the outer diameter of the stabilisers and cleaning members (brushes 38 etc.) can be adjusted to be a close fit with the same. The work string incorporating the apparatus is then run into the well, until the cleaning device assembly is in the location of the tubular to be cleaned, and the work string is then rotated in a clockwise direction from the top-drive of the well, to drive the cleaning device assembly in rotation relative to the tubular. The pads bearing the cleaning members rotate against the inner surface of the wellbore and clean debris from the walls of the borehole.

A clockwise helical arrangement of the brushes 38 on the pads 31 means that as the work string is rotated in a clockwise direction, the brushes clean the inner surface of the wellbore tubular extremely effectively, as the narrow edges of the brushes are driven into the layer of debris on the wall as the string rotates. Debris dislodged from the inner surface of the wellbore is diverted into the channels between adjacent brushes, and is urged up the wellbore for recovery from the well by means of the helical arrangement. Optionally, the presentation of the thin ends of the brushes to the debris attached to the wall concentrates the force from the resilient springs supporting the pads into a relatively small area on the wall of the tubular, and therefore more of the debris is dislodged and carried to the surface through the helical channels. Alternatively, the pads can be switched so that the helical arrangement of the slots and the cleaning members (e.g. the brushes) is anticlockwise. Running the tool in the hole with an anticlockwise helical arrangement of slots and brushes and then rotating the string in a clockwise direction as is conventional for most wells means that the flat face of the brushes is presented to the inner surface of the wellbore being cleaned, so that the cleaning effect is distributed over are relatively wide area of the wellbore inner surface. Any of the pads described herein can be formed with either clockwise or anti-clockwise helical arrangements of slots. The cleaning members, e.g. the brushes and blades, can be slotted into either. The sub can optionally incorporate some pads with clockwise arrangements and some with anticlockwise arrangements of slots and cleaning members. The stabiliser bodies spaced on either side of the cleaning device assembly remain stationary with respect to the wellbore during the cleaning operation, and allow the body of the sub 1 to rotate within their bores. The stabiliser assemblies do not compress radially and so maintain a constant standoff between the cleaning pads and the inner surface of the wellbore, so that the brushes 38 etc. engage the inner surface but the solid pad bodies 31 retained in the recesses do not, thereby allowing and promoting continuous rotation with reduced risks of snagging the pad bodies 31 on the inner surface of the tubular being cleaned.

Optionally the work string can be axially reciprocated in the wellbore with or without being rotated at the same time, and in certain circumstances, the work string can also be driven in rotation without being axially advanced into the wellbore. The circumferential coverage of the pads 31 maintains the standoff around the whole circumference reducing the risks of bottoming out of the string when a ledge or another incursion into the nominal inner diameter of the wellbore is encountered. The ramps on the axial ends of the cleaning members help to maintain the standoff as the string rides axially over ridges and tool joints etc.

The cleaning pads 31 remove the particulate matter from the inner surface of the wellbore, and optionally the cleaning operation is carried out with a circulation sub in the work string (optionally below the sub 1) which promotes upward flow of the fluid that is pumped from surface down the central bore 10b of the string and out of the circulation sub, and is then diverted up the annulus between the work string and the tubular being cleaned. The particulates being removed from the wall of the wellbore are therefore washed up the annulus to the surface, where they are optionally recovered in mud processing apparatus. Any particulates dropping out of suspension while still in the annulus are optionally trapped by the junk catcher 5, and are removed from the well with the string when the cleaning operation is finished. The junk catcher 5 packs the particulate matter more densely in a chamber as a result of the relative movement of the inner and outer walls agitating the junk trapped therein. This reduces escape of the junk during tripping out of the hole, when optionally the inner body 10 would not be rotating, and ensures that the junk trapped in the chamber is more likely to be retained therein, and is more likely to be representative of the true conditions in the wellbore, particularly with respect to particulates. Also, the resilient wiper optionally folds flat when running the sub 1 into the hole, thereby reducing running in speeds and forces, and expands radially into the configuration shown in the drawings only when pulling out of the hole, so that the junk is channelled more effectively into the junk catcher for recovery to the surface, and is not pushed ahead of the sub 1.

Metallic particulates and larger metal pieces are attracted by the magnets 26, 46, and are thereby retained on the outer surface of the sub 1. These are also recovered from the well with the string after completion of the cleaning operation.

Referring now to figures 13-20, another example of a cleaning device in the form of a cleaning pad for use in the sub 1 is disclosed. The cleaning pad 41 shown in these figures is similar to the cleaning pad 41 described above, and similar features that are common to both will not be described in detail here. However, briefly, the pad 41 has a body 45, and slots 47 for receiving cleaning members. The cleaning members in this example are blades 48. The slots 47 have a similar dovetail profile to the slots 37, and are again open at the side edges of each pad. The blades 48 are inserted into the pads before use by sliding the head 48h of a blade 48 into a respective slot as previously described, filling the slots, and are retained in the slots by the walls of the recess in the body. The slots 47 have a helical pattern as described above for the slot 37.

Optionally the blades 48 comprise resilient metal strips, optionally formed from spring steel or the like, and which are optionally formed in lengths that are roughly twice the distance between the desired radial outer edge of the blade 48, and the tip of the head 48h. The blades 48 are optionally formed by arranging the strips in spaced apart locations along the length of the mouth of a generally U-shaped channel 48c which will form the head of the cleaning member, and pressing the central portion of each strip into the U-shaped channel 48c using the retaining bar. The retaining bar is pressed the down into the U-shaped channel 48c on top of the central portion of the strip as far as possible, and then the U-shaped channel 48c is crimped at the top in a press so as to close the neck of the U-shaped channel 48c around the protruding strips. The closure of the neck prevents the escape of the bar from the crimped U-shaped channel 48c, and the double-sided folded arrangement of the strip is therefore trapped within the channel 48c. Figure 16 shows a cross- sectional schematic arrangement of a optional blade head 48 formed by this manner. The lateral ends of each head are closed by crimping, or pressing, or swaging the ends of the channel 48c, so that no lateral movement of the strips or the bar is permitted with respect to the channel 48c. Optionally, the channel 48c can be filled with adhesive, or other filler which helps to pack the space within the channel 48c, and enable it to resist compressive forces more easily.

Optionally the blade heads 48h are formed in sections that are similar in length to the slots 47, so that one slot 47 optionally accommodates a single cleaning member, which extends from one end of the slot 47 to the other. Filling the slots 47 with a single cleaning member in this manner reduces the extent of lateral movement of the cleaning member within the slot, and is therefore an advantage.

The blades 48 are relatively inflexible in comparison to the brushes, but still optionally incorporate a certain amount of resilience as an inherent property of the material. However, the folded configuration makes the blades 48 stiffer. Optionally the strips of resilient sheet steel used to form the blades are approximately 0.5 to 5mm thick, for example 1 to 2 mm, approximately 2 to 10 mm in width, for example 3 mm in width, and approximately 50 - 100 mm in length, for example 70 to 80 mm in length. Optionally, the strips laid flat onto the mouth of the channel to be pressed into it in order to form the blades can be spaced apart from one another by less than 1 mm, thereby forming small gaps between each adjacent strip on each blade.

Forming small gaps in this way in the blades increases the resilience of the blades. The width of the blade sections, the lateral length of the blades sections along the blade, and the stiffness of the material, can all be modified in different examples of the invention to enhance the resilient qualities of the blades, depending on the particular usage of the device. In some circumstances, it can be useful for the blades to be more or less resilient than other circumstances. For example, while rigid blades with very little flexibility and resilience are useful for scraping hard materials, and resisting wear, they tend to "bounce" over obstacles such as joints between adjacent wellbore tubulars, which results in build-up of debris underneath such joints over which the blade has "bounced". Increasing the resilience of the blade maintains the contact between the blade and the inner surface of the wellbore being cleaned, thereby enhancing the cleaning characteristics of these resilient blades, in comparison to rigid inflexible blades.

The double-leaf folded feature of the blades, formed by the end sections of the strip (the leaves) being brought together by the insertion of the bar into the mouth of the channel is another useful feature, because under high pressures applied to each blade, the leaves can tend to move relative to one another, and enhance the scraping characteristics, because two parallel scraper faces are being presented to the wellbore surface rather than one. The relative movement of the two leaves in each blade also enables the blade to be self-cleaning. The blades 48 are removable from the pads and can be replaced as the pads are removed for redressing the tool.

In use, the sub 1 incorporating the blades 48 is connected into a tool string or work string which may optionally incorporate other cleaning tools or tools that have other functions, and deployed in a wellbore lined with casing C to be cleaned. The pads bearing the blades 48 rotate against the inner surface of the wellbore and clean debris from the walls of the borehole.

A clockwise helical arrangement of the blades 48 on the pads 41 has the same advantages as previously described in relation to the brushes 38. The helical arrangement of the slots and the blades can be switched to clockwise or

anticlockwise. In the case of the blades 48, a single steel strip is inserted into the channel at spaced apart locations. In one possible modification of this example, more than one steel strip can be inserted as a stack of strips at each location on the channel, to create a blade having more than two leaves, for example 4, 6, or more. Optionally, the thickness of the sheets of blade forming material can be reduced in order to accommodate the stack of strips within the U-shaped channel. A schematic representation of this arrangement showing the strips before and after insertion into the channel 58c is shown in figures 17 and 18. One advantage that can be obtained by this arrangement is that each leaf in the blade can act as an individual scraper surface acting to clean the inner surface of the wellbore tubular, and the relative movement of the leaves within the blade 58 can have a self-cleaning effect to avoid excessive debris accumulating on the blade, and reducing its cleaning effect. The remaining features of this modified example are as previously described with respect to the other characteristics of the device, and the reader is referred to the earlier description in relation to those other features, which can be combined with this modification as described.

In another possible modification, instead of being formed from separate strips (or stacks of strips) spaced apart along the length of the channel, the blade can comprise a single continuous sheet extending the length of the channel, and restrained within the channel by the rod pressing the central portion of the sheet into the channel as described in relation to the other examples above. In this example, there are no gaps along the blade. The remaining features of this modified example are as previously described with respect to the other characteristics of the device, and the reader is referred to the earlier description in relation to those other features, which can be combined with this modification as described above.

In another modification shown schematically in Fig 19, the blades are optionally non-symmetrical. In the Fig 19 arrangement, separate sheets 68s are used to form the blades, but instead of being spaced apart along the blade, each sheet 68s overlaps with at least one of its adjacent neighbours on either side. Optionally, the direction and extent of overlap is consistent along the length of the blade, so that along the length of the blade, the leading end of each sheet underlies the trailing end of the next sheet 68s. Alternatively, the leading end of each sheet 68s can overlie the trailing end of the next sheet. Accordingly, the leaves are non-parallel and diverge from the axis of the blade as a result of the overlap, optionally in the same direction. This modification optionally allows certain advantages, particularly when used in blades that extends helically in the same rotational direction as the direction of rotation of the work string, and particularly when the leading ends of the sheets overlie the trailing ends of the next adjacent sheet, because the "edge-on" presentation of the non-parallel blades creates a more aggressive cutting and cleaning surface than the opposite arrangement where the leading ends of the sheets the trailing ends underlie the trailing ends of the next adjacent sheets. The corrugated effect of the overlapped blades also has a more aggressive cleaning effect in other configurations that do not have slots extending helically in the same direction as the intended rotation of their work string. The blades can be inserted into the pad in either direction, allowing considerable flexibility on site for matching of the local conditions in the hole, without carrying excessive amounts of stock of different pads, brushes, and scrapers. This modification is equally appropriate to the stacked sheet variant.

Figure 20 shows an alternative arrangement of a cleaning device in the form of a cleaning pad 71 suitable for use in any of the examples described herein, and which shares features in common with the other examples of cleaning pads, which will not be described here. One difference in the figure 20 example is that the side profile of the slots is L-shaped rather than dovetailed. One optional feature of the cleaning pad 71 is that the leading blade at the lower end of the pad 71 has the ramp to facilitate riding of the pad 71 over obstacles and inconsistencies on the inner surface of the wellbore being cleaned during axial insertion of the sub 1 into the well. The ramp reduces the tendency of the leading blade to become damaged. The ramps on the leading blade can be an optional feature in any of the examples described, but is particularly useful in relation to the examples incorporating blades rather than brushes, because of the increased stiffness of the blades. Optionally the ramp is only formed in the leading blade, leaving the remaining blades axially spaced from the leading blade to scrape the inner surface of the wellbore. Figure 20 shows a similar example of another version of cleaning pad 81, having a similar ramp in the leading blade, but having an alternative profile of slot, which in this example has an inverted T-shape, which can also be used in any of the examples described herein. The inverted T shape can have flat sides or angled sides.