WO2019234126A1

WO2019234126A1 - Attachment device

Info

Publication number: WO2019234126A1
Application number: PCT/EP2019/064720
Authority: WO
Inventors: Ken Erik STEINE
Original assignee: Ace Oil Tools
Priority date: 2018-06-06
Filing date: 2019-06-05
Publication date: 2019-12-12
Also published as: GB201809317D0

Abstract

An attachment assembly for attachment to an internal surface of a pipe, comprising a first attachment element comprising a tubular body and a plurality of gripping arms extending axially away from the tubular body and arranged to deflect radially outwards; and, a second attachment element adapted to slide at least partially within the first attachment element, wherein when at least a portion of the first attachment element and the second attachment element are arranged axially within the pipe and pressed together each of the plurality of gripping arms is deflected radially outwards by the second attachment element to grip the pipe and thereby secure the attachment assembly to the internal surface of the pipe.

Description

ATTACHMENT DEVICE

BACKGROUND

In oil and gas extraction, a casing string is inserted into a drilled wellbore. Casing strings are often provided with additional equipment, which must be connected to the pipe. Various techniques exist for attaching equipment to casing strings, including threads, welding, pins or screws, and friction, the latter of which can be in the form of an interference fit or clamping.

Threaded connections are most common for several applications and must be manufactured to a high degree of tolerance to reduce error and ensure effective mounting, particularly under load. Using threaded connections also means that different equipment must be manufactured for each different casing. The many different sized threads introduce significant expense and inventory overheads. The casing string must also be provided with a thread, which makes manufacture inefficient as threaded casings have to be welded onto the casing string.

An example use of threaded connections is to mount float equipment to the end of a casing string, with such float equipment used to guide the casing string past ledges and slough zones, to provide a landing point for cementing plugs, and to provide a back pressure valve to prevent cement from flowing into the inner diameter of the casing.

Welded connections are slow and labour intensive, and can be technically challenging. Welding also risks affecting the structural integrity of the casing string, as the welding process subjects the casing string to extreme heat and causes permanent deformation. Attaching equipment with pins or screws is also labour intensive, requiring the insertion of the pins or tightening of the screws, and can lead to protrusions in the equipment, which is undesirable when space is limited. The maximum holding force of equipment attached with pins or screws is limited by the diameter and material of the pins or screws, which is in turn limited by the size of the equipment being attached. Connections that use an interference fit generally require that part of the equipment is heated in order to temporarily expand it, which can be time consuming and requires specialist equipment.

Welding, pins or screws and friction connections can all be used to secure function elements, such as centralisers, to the exterior of the casing string. Function elements can either be directly connected to the casing string, or they can be restrained between a pair of stop-collars, with the stop collars being directly connected to the casing string. When restrained between a pair of stop- collars, the function element is typically fixed axially but free to rotate about the casing string. The use of stop collars and function elements, such as centralisers, is well known.

There is a need for devices and methods for attaching equipment to a casing string that do not require labour intensive installation and do not require modification of the casing string or protrude from the external surface of the casing string.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, there is provided an attachment assembly for attachment to an internal surface of a pipe, comprising: a first attachment element comprising a tubular body and a plurality of gripping arms extending axially away from the tubular body and arranged to deflect radially outwards; and, a second attachment element adapted to slide at least partially within the first attachment element, wherein when at least a portion of the first attachment element and the second attachment element are arranged axially within the pipe and pressed together each of the plurality of gripping arms is deflected radially outwards by the second attachment element to grip the pipe and thereby secure the attachment assembly to the internal surface of the pipe.

Attachment in this way allows the assembly to be connected to the pipe, most importantly, without protruding from the external surface of the pipe and without requiring significant modification to the pipe. Importantly, the pipe is not significantly deformed by the connection. The device is attached to the internal surface of a casing string by merely pressing the second attachment element into the first attachment element. No pins, screws or welding are required.

In addition, the attachment of the gripping arms to the pipe due to the deflection of the arms allows a very strong gripping force to be applied to the pipe. The attachment mechanism delivers extremely high holding forces under all operating conditions and is able to withstand substantial axial load. Further advantages include the simple and low cost of construction and ease of application and installation in working environments.

The connection of the invention is independent of weight, grade and thread. The diameter of the attachment assembly can be manufactured within a relatively wide tolerance range as the variable outer circumference of the assembly allows it to be easily attached to casing strings with different inner diameters without affecting the external profile of the pipe.

Preferably, an outer diameter of the second attachment element is tapered to form a conical abutment face and a narrow end of the second attachment element has an outer diameter less than an inner diameter of the plurality of gripping arms of the first attachment element.

The internal diameter of the plurality of gripping arms is the diameter of the largest circle that can fit within the tubular region defined by the gripping arms. This corresponds to the distance between a pair of directly opposing gripping arms when there are even numbers of gripping arms.

The tapered shape of the second attachment element causes the gripping arms to be deflected outwards by abutment against the abutment face as the second attachment element is pressed into the first attachment element. The outer diameter varies depending on how far the second attachment element is inserted into the first attachment element. As the second attachment element is pressed further into the first attachment element, the magnitude of the outward deflection of the gripping arms increases, thereby causing the outer diameter of the assembly to increase. Even more preferably, the attachment assembly further comprises a plurality of circumferential ridges on an inner wall of the plurality of gripping arms arranged to cooperate with a corresponding plurality of circumferential ridges on an outer wall of the second attachment element to form a ratchet.

The ridges may be pawls or serrations for example. The ratchet ensures that the second attachment element remains axially secured within the first attachment element such that the gripping arms are maintained in a deflected position to grip the pipe. Moreover the axial load which the assembly can withstand is significantly increased by the abutment of a circumferential ridge of the second attachment element against a circumferential ridge of the first attachment element. The ridges on the first attachment element may alternatively be on an inner wall of the tubular body of the first attachment element.

Preferably, the plurality of circumferential ridges on the inner wall of the plurality of gripping arms is on a non-tapered portion of the inner wall of the plurality of gripping arms, and the corresponding plurality of circumferential ridges on the outer wall of the second attachment element is on a non-tapered portion of the outer wall of the second attachment element.

Having the circumferential ridges on non-tapered portions increases the strength of the engagement between corresponding circumferential ridges compared to having them on tapered portions. Having the circumferential ridges on non- tapered portions also means the angle of the ratchet mechanism does not vary as much when the two elements are pressed together and ensures that the ratchet engages over a wider range of insertion magnitudes when the second attachment element is inserted into the first attachment element.

Preferably, each of the plurality of circumferential ridges on the inner wall of the plurality of gripping arms comprises a sloped first side face facing a distal end of the first attachment element and an opposite second side face forming an abutment surface perpendicular to a central axial of the second attachment element, and the plurality of circumferential ridges on the outer wall of the second attachment element have a complementary cross section to a cross section of the plurality of circumferential ridges on the inner wall of the plurality of gripping arms.

This increases the axial load that the attachment assembly can withstand. For example, if an axial load is applied to the second attachment element when the attachment assembly is installed, the perpendicular ridges of the second attachment element abut against the perpendicular ridges of the first attachment element, preventing the second attachment element from moving. The distal end of the first attachment element is the end towards which the gripping elements extend. Preferably, each gripping arm of the plurality of gripping arms comprises a plurality of gripping teeth arranged on an outer face of the gripping arm to grip the internal surface of the pipe.

The gripping teeth provide a force on the casing string when the assembly is installed that helps prevent axial or radial movement of the attachment assembly.

Each of the plurality of gripping teeth may optionally extend circumferentially around the outer face of the gripping arm. This provides a force on the casing string to prevent axial movement of the attachment assembly.

Each of the plurality of the plurality of gripping teeth may optionally comprise at least one longitudinal slit. Preferably, each of the plurality of gripping teeth comprises five longitudinal slits. These slits provide a force on the casing string when installed to prevent rotational movement of the attachment assembly.

Each of the plurality of gripping arms may alternatively or additionally be tapered to form a tapered inner face such that an inner diameter of the plurality of gripping arms decreases in a direction towards the tubular body. Preferably, the tapering angle of the gripping arms corresponds to the tapering angle of the second attachment element.

This tapering allows for more effective abutment between the surfaces of the first and second attachment elements. Preferably, the tapered inner face is arranged to protrude radially inward from the gripping arm, resulting in a rim on an inner surface of the gripping arm. This increases the contact area during abutment.

Optionally, there is a ridge on an outer surface of the first attachment element at a base of each of the plurality of gripping arms. The base of each gripping arm is the end of the gripping arm furthest from the tip.

Preferably, the plurality of gripping arms of the first attachment element is formed by a plurality of slits extending axially from a distal end of the first attachment element. Preferably, all of the plurality of slits are parallel to each other.

Optionally, the first attachment element may be a float equipment or a function element.

Optionally, the second attachment element may be a float equipment or a function element. This allows function elements, such as internal centralisers, and float equipment, such as reamer shoes, to be attached to the internal surface of a casing string by only pressing the second attachment element into the first attachment element. In addition, the diameter of the function elements and float equipment can be within a relatively wide tolerance range as the variable outer circumference of the assembly allows it to be easily attached to casing strings with different inner diameters.

When compared to conventionally mounted float equipment with threads, the mount of the present invention allows the equipment to be mounted to different size casings, which reduces the need for multiple thread options and significantly reduces the cost of equipment manufacture and inventory overheads.

Additionally, conventional threaded float equipment takes a long time to install as the equipment must be threaded onto the casing. Installation of the present invention is quick and easy and dramatically increases the speed of installation and reduces the overall installation time. Any type of shoe or equipment can be used on the tubing rather than being limited to one type.

Most importantly, attaching on the inner surface of the casing string advantageously allows float equipment to be installed flush with the outer surface of the casing string, which is beneficial when there is limited clearance around the casing string.

According to a further aspect of the invention, there is provided a method of mounting the attachment assembly to a casing string comprising positioning the first attachment element and the second attachment element inside the casing string and press-fitting the second attachment element into the first attachment element such that contact between the first and second attachment elements causes each of the plurality of gripping arms of the first attachment element to deflect radially outwards.

Press-fitting comprises moving the first and second attachment elements relatively toward each other. Preferably, the first attachment element is held in a fixed position relative to the pipe and a force is applied to the second attachment element to push it into the first attachment element. Alternatively, the second attachment element may be held in place and the first attachment element may be pushed over it, or both elements may move toward each other simultaneously.

Installation using this method is quick and easy and dramatically increases the speed of installation and reduces the overall installation time compared to threaded or welded connections.

BRIEF DESCRIPTION OF DRAWINGS

Examples of the present invention will now be described in detail with reference to the accompanying drawings, in which:

Figure 1 shows an attachment assembly comprising first and second attachment elements;

Figure 2a shows a cutaway view of the assembly from Figure 1 with the first and second attachment elements separated; Figure 2b shows a close-up cutaway view of the assembly from Figure 1 with the first and second attachment elements separated;

Figure 3a shows a close-up cutaway view of a gripping arm of the first attachment element of Figure 1 prior to being deflected by abutment against the second attachment element of Figure 1 ;

Figure 3b shows a close-up cutaway view of a gripping arm of the first attachment element of Figure 1 after being deflected by abutment against the second attachment element of Figure 1 ;

Figure 4 shows a close-up cutaway view the attachment assembly of Figure 1 gripping to an inner surface of a pipe;

Figure 5 show a tool that can be used to install an attachment assembly;

Figure 6 shows an alternative view of the tool in Figure 5; and,

Figure 7 shows another alternative view of the tool in Figures 5 and 6.

DETAILED DESCRIPTION

The present invention provides an improved attachment device for a pipe, in particular for attaching float equipment and other function elements, such as an internal centraliser, in downhole tubular bodies. The attachment device is for attachment to the internal surface of a casing string and may either be integrated into a function element or used as a stop to secure a function element in such a way that it is axially restrained but free to rotate, with one attachment device positioned at either end of the function element.

The words pipe, tubular, casing string, casing, tubing and tubing string may be used interchangeably throughout the present description to refer to a casing, the length of which is typically referred to as the casing string which is run into a well bore and to which float equipment and function elements are mounted. The words attachment device and attachment assembly may also be used interchangeably throughout the present description to refer to embodiments of the invention.

In the following description, the attachment device is described in relation to a stand-alone device intended to be fixed to the inner surface of a casing string and abut axially against a function element to restrict the axial movement of the function element within the casing string, but it is equally valid to consider the attachment device integrated into a function element, float equipment or other downhole equipment that is fixed within a pipe.

Figure 1 shows an attachment assembly 100 comprising two substantially tubular parts, namely cooperating first attachment element 101 and second attachment element 102. In use, the attachment elements 101 and 102 are coaxially aligned and press-fit together within a pipe or other tubular, such that the second attachment element 102 is at least partly inside the first attachment element 101.

A pair of such attachment assemblies 100 can be used to axially constrain a function element, wherein the attachment assemblies 100 are fixed to the inner surface of a casing string on opposing sides of the function element such that the function element is free to rotate within the casing string. Alternatively, cooperating interlocking sections (not shown) can be provided on one or both of the attachment assemblies and on the function element to also restrict rotational movement of the function element. In an alternative embodiment (not shown), one of the attachment elements 101 and 102 may be integrated into a function element such that the attachment assembly can be used to restrict rotational and axial movement of the function element.

The attachment assembly 100 attaches to an internal surface of a pipe or other tubular through a plurality of gripping arms 201 on the first attachment element 101 , which are shown in Figures 2a and 2b. The gripping arms are arranged to be deflected, or bent, radially outward by abutment against the second attachment element 102, thereby gripping to the internal surface of the pipe and holding the attachment assembly in place, as best seen in Figure 4.

The gripping arms 201 extend axially away from a tubular body 209 of the first attachment element 101 and are formed by a plurality of equal length, linear and axially aligned slots, with one gripping arm 201 formed between each pair of adjacent slots. Alternative embodiments are envisaged in which the gripping arms are of different shapes, such as substantially triangular, i.e. forming a point, or curved. In the illustrated embodiment, there is an optional ridge 212 the base of each gripping arm on the outer surface of the first attachment element 101 , best seen in Figure 2b.

To deflect the gripping arms 201 radially outwards, a section of the outer wall of the second attachment element 102 is tapered along its longitudinal axis to form a tapered outer wall 202, and is therefore shaped like part of the surface of the cone. When the attachment elements 101 and 102 are press-fit together, a tapered abutment face 203 of the tapered outer wall 202 abuts against an inner face 204 of each gripping arm 201 of the first attachment element 101 , causing the gripping arms 201 to deflect radially outward.

The tapering of the second attachment element 102 means that one end of the second attachment element 102 is narrower than the other. The outer diameter of the narrow end 205 is less than an inner diameter of the first attachment element 101 defined by the inner surfaces of gripping arms 201 , thereby allowing the second attachment element 102 to be press-fit into the first attachment element 101. The inner diameter of the second attachment element 102 is constant along its length in the embodiment shown in Figure 2a and 2b, such that the tapering causes one end of the second attachment element's sidewall to be thicker than the other. In an alternative embodiment, the sidewall of the second attachment element 102 may be the same thickness for the entirety, including the section with the tapered outer wall 202, such that the inner diameter is not constant along its length (i.e. the inner wall could also be tapered).

To improve the abutment between the gripping arms 201 and the tapered abutment face 203, the gripping arms 201 are partially angled or tapered, with a larger inner diameter at the tip of the arm, such as shown in Figures 2a and 2b. In this way, the tapered arms may more effectively abut the tapered abutment face 203 of the second attachment element 102. The pitch angles of the tapered gripping arms 201 and the tapered abutment face 203 are preferably the same to maximise surface-area contact during abutment.

The abutment between the tapered abutment face 203 and the inner face 204 of the gripping arms 201 is further enhanced by arranging the inner face 204 to protrude radially inward from the gripping arm 201 , resulting in a rim 211 on the inner surface of the gripping arm 201. This effectively reduces the inner diameter defined by the plurality of gripping arms 201 and increases the contact area between the first and second attachment elements 101 and 102. The reduced inner diameter of the gripping arms 201 also increases the deflection of the gripping arms 201 when the pitch angle of the tapered abutment face 203 is shallower than the pitch angle of the tapered inner face 204.

To ensure that the second attachment element 102 remains in place once press- fit into the first attachment element 101 , the assembly 100 is provided with a ratchet system. A plurality of ridged grooves/raised ridges or pawls 206 are provided on the inner surface of the first attachment element 101 , and a corresponding plurality of ridged grooves/ raised ridges or pawls 207 are provided on an outer surface of the second attachment element 102, extending around its outer circumference. The ridges or pawls 206 on the first attachment element 101 and the ridges or pawls 207 on the second attachment element 102 together form the ratchet system, which can be seen engaged in Figure 3b. When the second attachment element 102 is pressed into the first attachment element 101 , the ratchet holds the second attachment element 102 in position relative to the first attachment element 101.

The ridges 206 are positioned on the inner surface of the gripping arms 201 such that the gripping arms 201 yield and allow the opposing ratchet sections 206 and 207 to engage when the first and second attachment elements 101 and 102 are pressed together. In the illustrated embodiment, the ridges or pawls 206 of the first attachment element 101 are on a non-tapered portion of the inner surface of the gripping arms 201 , in this case positioned at the proximal end of the gripping arms 201 where the gripping arms 201 attach to the tubular body 209. The corresponding ridges or pawls 207 on the second attachment element 102 are on a non-tapered portion at the narrow end 205 of the outer surface of the second attachment element 102.

In the preferred embodiment shown in the figures, the ridges 206 and 207 are asymmetric so as to allow the two elements 101 and 102 to be pressed together but prevent them being pulled apart. Each of the ridges 206 and 207 has a sloped first side face and an opposite second side face that forms an abutment surface or shoulder perpendicular to the central axis of the assembly.

On the first attachment element 101 , the perpendicular second side faces of the ridges 206 face away from the tapered faces 204 at the distal ends of the gripping arms 201 , and the sloped first side faces of the ridges 206 face towards the tapered faces 204 of the gripping arms 201.

On the second attachment element 102, the perpendicular second side faces of the ridges 207 face towards the tapered portion 203 of the second attachment element 102 and the sloped first side faces of the ridges 206 face away from the tapered portion 203.

The axial load that the attachment assembly 100 can withstand is significantly increased by the abutment of a ridge 207 of the second attachment element 102 against a face of a ridge 206 of the first attachment element 101 perpendicular to the central axis of the assembly 100. For example, if an axial load is applied to the second attachment element 102 when the attachment assembly 100 is installed, the ridges 207 of the second attachment element 102 abut against the ridges 206 of the first attachment element 101 , preventing the second attachment element 102 from moving.

In addition to the ratchet system, the first attachment element 101 also comprises a raised lip 210 that prevents the second attachment element 102 from being over-inserted during installation of the assembly 100, acting as a barrier that abuts the narrow end 205 of the second attachment element 102. This abutment between the raised lip 210 and the second attachment element 102 is visible in Figure 3b, where the second attachment element 102 has been fully pressed into the first attachment element 101.

To assist with gripping to the inner surface of a pipe or other tubular, the outer surface of the gripping arms 201 may be rough, as seen in Figure 2b. In Figure 2b, the gripping arms 201 comprise a plurality of teeth 208a-c that grip the inner surface of a pipe or casing when the gripping arms are bent outward. The teeth 208a-c are formed by a plurality of circumferential protrusions on the outer part of the tips of the gripping arms 201 , and help to restrict axial movement of the assembly 100 relative to the pipe by creating an edge that exerts a force on the pipe.

Embodiments are envisaged where the circumferential teeth 208a-c further comprise a series of longitudinal slits (not shown). Such longitudinal slits help to prevent rotational movement of the assembly 100 by creating additional edges that exert a force on the pipe when the attachment assembly 100 is installed.

The close-up cutaway views in Figures 3a and 3b show the interaction between attachment elements 101 and 102 when they are pressed together. In Figure 3a, the second attachment element 102 is loosely pressed into the first attachment element 101 such that the tapered inner face 204 of the gripping arm 201 of the first attachment element 101 abuts against the tapered abutment face 203 of the second attachment element 102, with the ridges 206 and 207 not yet engaged.

In Figure 3b, the attachment elements 101 and 102 are pressed together further than in Figure 3a, which is the installed configuration of the assembly 100. The gripping arm 201 is deflected radially outwards by abutment against the tapered gripping face 203, and the ridges 206 and 207 are engaged at region 301 , thus preventing the two attachment elements 101 and 102 from separating. The second attachment element 102 is fully pressed into first attachment element 101 such that the narrow end 205 of the second attachment element 102 is abutting against lip 210, although this is not always necessary for installation.

The magnitude of the deflection of the gripping arms 201 is dictated by how far the second attachment element 102 is pressed into the first attachment element 101. The further the second attachment element 102 is pressed into first attachment element 101 , the further gripping arm 201 will be deflected, which allows the attachment assembly 100 to be installed for a range of pipe inner diameters.

The number of ridges or pawls that engage when the assembly 100 is installed depends on how far the second attachment element 102 is pressed into the first attachment element 101 ; ideally at least one set of ridges will be engaged. The maximum deflection of the gripping arms 201 occurs when the narrow end 205 of the second attachment element 102 is abuts lip 210, as shown in Figure 3b.

During installation, the second attachment element 102 is pressed into the first attachment element 101 until the gripping arms 201 have been sufficiently deflected to grip to the pipe, i.e. how far the second attachment element 102 needs to be pressed into the first attachment element 101 depends on the inner diameter of the pipe in which the assembly 100 is to be installed. Additionally, the gripping strength for a given diameter of pipe depends on how far the second attachment element 102 is pressed into the first attachment element 101. Pressing the second attachment element 102 further into the first attachment element 101 will increase the force exerted by the second attachment element 102 on the gripping arms 201 , which will in turn increase the normal reaction force between the gripping arms 201 and the inner surface of the pipe, thereby increasing the frictional force holding the assembly 100 in place.

Figure 4 shows a cutaway view of the attachment assembly 100 installed within a pipe 401. The gripping arm 201 is shown deflected radially outward by abutment against the second attachment element 102, which causes it to abut against the inner surface 402 of the pipe. In this preferred embodiment, the gripping teeth 208a-c assist in gripping the pipe 401 by increasing friction between the pipe and the assembly 100. The gripping arm 201 and/or the gripping teeth 208a-c may fully or partially embed into the pipe 401 depending on the strength of the materials of the pipe 401 and the assembly 100, and how far the second attachment element 102 is pressed into the first attachment element 101. Alternatively, the assembly 100 may be held in place within the pipe 401 by friction alone, without embedding in the pipe.

To allow the assembly 100 to be installed, the internal diameter of the pipe 401 must be larger than the outer diameter of the first attachment element 101 prior to the gripping arms 201 being deformed radially outwards.

The assembly 100 is installed in the pipe 401 by axially aligning the attachment elements 101 and 102 within the pipe 401 and press-fitting them together, which causes the gripping arms 201 to deflect radially outward towards the inner surface of the pipe. The two attachment elements are pressed together until the gripping arms 201 are deflected to sufficiently grip to the internal surface of the pipe 401 and hold the assembly 100 in place.

Press-fitting the two attachment elements 101 and 102 together requires a large compressive force in order to defect the gripping arms 201 and engage the ratchet system. Installation of the assembly 100 will therefore generally be performed using a specialist installation tool, such as the exemplary installation tool 500 illustrated in Figures 5-7.

Installation of the attachment assembly 100 is performed at any time prior to the pipe being inserted into the wellbore, for example at a pipeyard or other onshore or offshore facility. The attachment assembly 100 is installed within the pipe using the tool 500, and preferably used to secure float equipment or a function element such as an internal centraliser. The pipe is then lowered into the wellbore with the attachment assembly 100 and float equipment or function element secured in position within the pipe.

The exemplary tool 500 comprises a plurality of rods 501 , which are rotatable about their axes. A distal end of each rod 501 comprises a securing member

502 protruding radially from the rod, which in turn comprises a catching surface

503 for abutment against attachment assembly 100. In Figures 5-7, the catching surfaces 503 are shown abutting the second attachment element 102, but this arrangement could be reversed such that each catching surface 503 instead abuts against first attachment element 101.

To provide a compressive force to the two attachment elements 101 and 102, the tool 500 also comprises an abutment plate 504 that moves slidably along rods 501. The abutment plate 504 is connected to a piston 505 that provides a force on abutment plate 504 in a direction toward the distal end of rods 501 , thereby creating a compressive force between the abutment plate 504 and the catching surface 503. The other end of the piston 505 is connected to an end plate 506, which is fixed at the proximal end of rods 501. The piston 505 may be driven hydraulically or otherwise, for example with an electric motor. Alternative embodiments are envisaged where the securing members 502 engage with grooves or notches (not shown) on the inner surface of the first or second attachment elements 101 or 102 instead of abutting an end of the first or second attachment elements 101 or 102. This is particularly advantageous where one of the elements 101 or 102 is substantially elongated, for example when integrated into a function element; this would otherwise require a longer installation tool.

To aid with installation of the assembly 100, the tool also comprises an alignment plate 601 , best seen in Figure 6, which holds the rods 501 in position relative to each other and holds the tool 500 in position relative to the attachment assembly 100. The outer diameter of the alignment plate 601 is preferably the same as, or very slightly less than, the internal diameter of the second attachment element 102, which allows it to be inserted through the second attachment element but reduces the tool's range of movement when inside the second attachment element.

To engage and disengage the securing members 502, a control plate 701 is connected to levers 702 at the proximal end of rods 501 , as shown in Figure 7. The control plate 701 comprises a plurality of slots 703 to which the levers 702 are slidably connected, i.e. the levers 702 slide within the slots 703, such that when the control plate 701 is rotated, the levers 702 slide within the slots 703, thereby causing rods 501 to rotate. This in turn causes securing members 502 to rotate between an engaged position, in which they point in a direction radially outward from the central axis of the tool 500, and an unengaged position, in which the securing members 502 do not point in a radially outward direction.

When installing the assembly 100 within a casing 401 using the tool 500, the first and second attachment elements 101 and 102 are inserted into the casing 401 at the location at which the assembly is to be installed, with the first and second attachment elements 101 and 102 and the casing 401 all axially aligned, and the second attachment 102 element inserted partially into the first attachment element 101. The distal end of tool 500 (i.e. the end with securing members 502) is then inserted axially through the centre of the attachment assembly 100 with the securing members 502 in the unengaged position and the abutment plate 504 retracted towards the proximal end of the rods 501. The tool 500 can be inserted from either side of the attachment assembly 100, but the installation procedure will be described with the tool 500 inserted from side of the first attachment element 101 (i.e. inserted through the first attachment element 101 first), as shown in Figures 5-7. The same procedure applies if the tool 500 is inserted from the side of the second attachment element 102.

Once inserted sufficiently, the securing members 502 are rotated into the engaged position by rotating control plate 701 in a direction that is anticlockwise from the perspective shown in Figure 7. The tool 500 is then positioned with the catching surface 503 of each securing member 502 abutting against the second attachment element 102.

The piston 505 is then activated to move the abutment plate 504 towards the distal end of the tool and bring the abutment plate 504 into abutment with the first attachment element 101. The piston 505 then continues to provide a force on the abutment plate 504, directed toward the distal end of the tool 500, to press-fit the two attachment elements 101 and 102 together. Preferably, first attachment element 101 remains in a fixed position relative to the casing 401 and the second attachment element 102 moves into the first attachment element 101. Alternatively the second attachment element 102 may be held in a fixed position relative to the casing 401 and the first attachment element 101 may be moved over the second attachment element 102, or both attachment elements 101 and 102 may move towards each other simultaneously.

As the second attachment element 102 is pressed into the first attachment element 101 , the conical outer portion of the second attachment element 102 abuts against the inner surface of the gripping arms 201 and causes the gripping arms 201 to defect radially outward and grip to the internal surface of the pipe 401. Once the assembly 100 is suitably attached, i.e. the gripping arms 201 have been deflected sufficiently to grip the pipe 401 , the securing members 502 are rotated back into the unengaged position by rotating control plate 701 clockwise, and the tool 500 is axially retracted through the centre of the assembly 100 and removed.

The attachment assembly 100 may be installed once the casing 401 is downhole, or may alternatively be installed prior to the casing 401 being inserted into the wellbore.

Although installation of the assembly 100 has been described with reference to the exemplary tool 500 in Figure 5-7, any tool or tools capable of providing a sufficient force to press-fit the two attachment elements 101 and 102 together such that the gripping arms 201 grip against the inner surface of the pipe 401 may be used instead, such as an expanding claw or finger-based mechanism.

The attachment assembly according to embodiments of the invention is suitable for industrial applications, in particular for use in the subsea oil and gas industry. The device may be made of any material suitable for such applications, such as steel, and the dimensions of the components described may be adapted as required.

Claims

1. An attachment assembly for attachment to an internal surface of a pipe, comprising:

a first attachment element comprising a tubular body and a plurality of gripping arms extending axially away from the tubular body and arranged to deflect radially outwards; and,

a second attachment element adapted to slide at least partially within the first attachment element,

wherein when at least a portion of the first attachment element and the second attachment element are arranged axially within the pipe and pressed together each of the plurality of gripping arms is deflected radially outwards by the second attachment element to grip the pipe and thereby secure the attachment assembly to the internal surface of the pipe.

2. An attachment assembly according to claim 1 , wherein an outer diameter of the second attachment element is tapered to form a conical abutment face and a narrow end of the second attachment element has an outer diameter less than an inner diameter of the plurality of gripping arms of the first attachment element.

3. An attachment assembly according to claim 1 or claim 2, further comprising a plurality of circumferential ridges on an inner wall of the plurality of gripping arms arranged to cooperate with a corresponding plurality of circumferential ridges on an outer wall of the second attachment element to form a ratchet.

4. An attachment assembly according to claim 3, wherein the plurality of circumferential ridges on the inner wall of the plurality of gripping arms is on a non-tapered portion of the inner wall of the plurality of gripping arms.

5. An attachment assembly according to claim 3 or claim 4, wherein the corresponding plurality of circumferential ridges on the outer wall of the second attachment element is on a non-tapered portion of the outer wall of the second attachment element.

6. An attachment assembly according to any of claims 3 to 5, wherein each of the plurality of circumferential ridges on the inner wall of the plurality of gripping arms comprises a sloped first side face facing a distal end of the first attachment element and an opposite second side face forming an abutment surface perpendicular to a central axis of the second attachment element, and wherein the plurality of circumferential ridges on the outer wall of the second attachment element have a complementary cross section to a cross section of the plurality of circumferential ridges on the inner wall of the plurality of gripping arms.

7. An attachment assembly according to any preceding claim, wherein each gripping arm of the plurality of gripping arms comprises a plurality of gripping teeth arranged on an outer face of the gripping arm to grip the internal surface of the pipe.

8. An attachment assembly according to claim 7, wherein each of the plurality of gripping teeth extends circumferentially around the outer face of the gripping arm.

9. An attachment assembly according to claim 8, wherein each of the plurality of gripping teeth comprises at least one longitudinal slit.

10. An attachment assembly according to claim 9, wherein each of the plurality of gripping teeth comprises five longitudinal slits.

11. An attachment assembly according to any preceding claim, in which each of the plurality of gripping arms is tapered to form a tapered inner face such that an inner diameter of the plurality of gripping arms decreases in a direction towards the tubular body.

12. An attachment assembly according to claim 11 , wherein the tapered inner face is arranged to protrude radially inward from the gripping arm, resulting in a rim on an inner surface of the gripping arm.

13. An attachment assembly according to any preceding claim, further comprising a ridge on an outer surface of the first attachment element at a base of each of the plurality of gripping arms.

14. An attachment assembly according to any preceding claim, wherein the first attachment element is a float equipment or a function element.

15. An attachment assembly according to any preceding claim, wherein the second attachment element is a float equipment or a function element.

16. An attachment assembly according to any preceding claim, wherein the plurality of gripping arms is formed by a plurality of slits extending axially from a distal end of the first attachment element.

17. A method of mounting the attachment assembly of any preceding claim to a casing string, the method comprising positioning the first attachment element and the second attachment element inside the casing string and press-fitting the second attachment element into the first attachment element such that contact between the first attachment element and second attachment element causes each of the plurality of gripping arms of the first attachment element to deflect radially outwards.