WO2014065677A1

WO2014065677A1 - A centralisation system

Info

Publication number: WO2014065677A1
Application number: PCT/NZ2013/000187
Authority: WO
Inventors: Gregory Douglas TROWBRIDGE; Geoffrey Neil Murray
Original assignee: Tdtech Limited
Priority date: 2012-10-24
Filing date: 2013-10-16
Publication date: 2014-05-01
Also published as: US20150275588A1; GB201506841D0; GB2521963A

Abstract

The present invention is directed to a tubular centralization system for completing oil, gas, geothermal and other types of wells where the temperatures may be high or the side loads are high, or both. The system is composed of a centralizer having a ring-shaped body with a plurality of wide ridges extending radially outwards from the main body, the ridges hollow along their length, and forming pockets on the inner surface, each ridge having at least one vane longitudinally aligned with the pocket and the axis of rotation, the vane or vanes extending radially inwards from the inner surface of the hollow ridge and having an inner edge aligned with a circumferential line that follows the circumference of the inner surface, a generally cylindrical stand-off band having a plurality of wide, straight ridges extending radially outwards from a portion of the outer surface, equi-spaced around the main body, the main body having a first part with the inner surface substantially parallel to the outer surface, and a second part that is tapered in profile, and a generally cylindrical stop collar for well bore holes, having a hollow main body formed from a first part that extends inwards from the first end and which has parallel walls, and a second part that extends inwards from the second end to meet the first part and which is tapered in profile, the outer surface of the second part tapering down to meet the inside surface, the taper having a first portion furthest from the second end that has a first angle between the inner surface and the outer surface, and a second portion closest to the second end with a greater angle between the first portion and the axis of rotation of the main body. The centralizer can also be ring-shaped with a plurality of elongate blades extending axially along the outer surface, each blade forming a wave form with at least two peaks and troughs along the length of the blade.

Description

A CENTRALISATION SYSTEM FIELD OF THE INVENTION

The present invention relates to a centralization system for centralizing tubulars in a well bore. More particularly, although not exclusively, the present invention relates to a centralization system structured so as to have an improved strength- to-weight ratio, and to have a load rating greater than that of equivalent systems currently known in the art. The present invention further relates to a centralization system that assists tubulars to pass over ridges inside a well bore, and which facilitates the rotation of tubulars inside a well bore.

BACKGROUND

When wells are drilled it is common for the inner surface of the as-drilled well bore to be rugose or ledged. When well completion tubulars such as casing or liner are run, the casing coupling(s) may get caught on the rough or ledged wall of the well to the extent that it may not even be possible to run the casing to the intended depth.

One currently available solution is to use a stop collar having a relatively long and tapered lead. However even at their maximum diameter, such items are smaller in diameter than the outside diameter of the casing couplings and are therefore of limited benefit in aiding casing couplings across ledges in the well bore. Additionally, the set screws in currently available stop collars are not contained such as to prevent them falling out. Should they fall out, the well may be threatened due to junk in the hole.

Some types of casing couplings are supplied with beveled edges in an attempt to reduce the risk of the coupling catching on ledges. However, the bevel leads tend to be very steep, and also the coupling usually still has a land, which can easily catch on well bore ledges. Therefore, this type of bevel is of somewhat limited benefit and may not prevent casing from catching. A key function of centralizers or stand-off rings is to substantially centralize tubulars within the well bore, thereby providing an annular space between the tubular(s) and the well bore into which a cement sheath is poured. A substantially even or uniform annular space is needed to ensure the quality of the cement sheath, which provides well zonal isolation and pressure integrity. When very large diameter casing is to be centralized, and particularly in a deviated well bore, close consideration needs to be given to the relative stiffness of the tubular. For example, and assuming a similar wall thickness, a 20" diameter casing will be 16 times stiffer than a 10" diameter casing.

Two types of centralizer are commonly used: a simple, low-cost bow-spring design, or a rigid blade/solid body design. Bow spring centralizers provide good centralization. However, they are not particularly strong and do not provide adequate restoration force for large diameter and stiff tubulars when run into tortuous or deviated well bores. The rigid blade type of design is rugged and works well even in deviated wellbores, but this type tends to be slightly more expensive and tends to get caught more easily on ridges or deviations than the bow spring type. Bow Spring type centralizers have bows that are made from tempered spring steel. This steel is too hard to easily drill or mill, should it become necessary to wash-over drill or sidetrack the well. It is common for rigid blade centralizers to be formed to include webs that extend radially outwards from the outer surface of the main body of the centralizer. These can be aligned axially along the body of the centralizer, as shown in Figure 1a, or helically spiralled around the body as shown in Figure 1 b. It is also known to have centralizers with helically spiralled blades having a variable pitch along their length, as described in US2011/0114338. One disadvantage of the helical design is that the edge of the rib presents a relatively square face to the formation as it is run into the well bore such that, as an example, a drill string with spiral bladed stabilizers will generate torque which exerts a rotational force on the drill string as it is run into the well bore.

The Finite Element Analysis calculated bending induced normal force at a single centralizer while running 18-5/8" x 136 pounds per foot casing into a deviated tortuous well bore has been shown to be >150,000 Ibsf. Conversely the required restoration force of an American Petroleum Institute (API) specification 10D Bow Spring Centralizer of this size is only 1 ,750 Ibsf (pounds per square foot), and the rating of the strongest currently available solid body type centralizer is only 50,000 Ibsf.

In High Temperature/High Pressure, Geothermal, Hot Fractured Rock, Huff ' N' Puff, Steam Assisted Gravity Drainage and other wells wherein the down-hole temperature is above 100°C, it is important to ensure that at no place in the well bore are there voids that could fill with water or a similar, low boiling temperature fluid. Should this occur, the trapped fluid may expand as the well heats up, creating pressures of greater than 10,000 psi. A number of solid body type centralizers, including the stronger, hydro-formed types, have voids such that in high temperature wells there is considerable risk of trapped fluid expansion causing the casing to collapse.

Sometimes when running casing, the float shoe (the valve assembly attached to the bottom of the tubular) may hang up on obstructions in the well bore. To avert this occurring, an elliptical shaped float shoe may be used which, when the casing is rotated, will enable the string to be eased past the down-hole obstruction. Currently centralizers are not available which enable the rotation of large diameter casing strings at high side loads and as a consequence, casing strings have not been landed that might otherwise have been, had rotation been possible.

Centralizers as are known in the art are formed from a variety of materials, including, but not limited to: aluminium, ductile iron, stainless steel, steel, and polyethylene plastic, depending on the intended use location and the environment at the use location (e.g. temperature etc). Plastic centralizers or metal centralizers with plastic friction reducing pads are usually used where reduced axial drag is required between the centralizer and the tubular. However, at very high side loads, this is not a realistic alternative for providing reduced axial drag as the loads far exceed the creep resistance capability of various plastics currently used. At very high side loads, plastics typically also fail quickly due to abrasion. Roller type centralizers are currently used to reduce axial and rotational friction. Such centralizers should not be used where very high side loads are anticipated as while the LoDRAG and LoTORQ type tools have a fail-safe mechanism to ensure they are not damaged, their effectiveness in high side-load situations, is reduced to that of regular sold body type centralizers. Those roller type tools without the fail-safe mechanism may actually be damaged and lead to junk in the well bore.

Centralizers designed with spiral or helical blades are intended to create turbulence and thus improve the quality of the cement sheath. The blade spiral however does have another significant disadvantage - that of ploughing and otherwise damaging cuttings beds, thus leading to the potential for fluid losses, high axial drag and differential sticking.

Many types of centralizers are too delicate to be installed other than on the rig floor. This may add considerable time and cost to the casing running operations, while also increasing operational hazards and risk. Additionally, most currently available centralizers do not have adequate axial compressive strength to cope with transferring the weight of a casing string, should the casing running elevators be run against the centralizer.

Many larger centralizers are heavy and difficult to handle and during installation, may result in back strain or other injuries to the installers.

Currently centralizer systems are regarded as "dumb iron" - they serve little more than to provide a means of running and cementing casing.

It is an object of the present invention to provide a casing centralization system which goes some way to overcoming the abovementioned disadvantages or which at least provides the public or industry with a useful choice.

It is a further object of the present invention to provide a casing centralization system that reliably centralizes all sizes of casing strings. It is a further object of the invention to provide a casing centralization system that can carry and store information relating to the tubular or tubulars with which it is associated.

It is a yet still further object of the invention to provide a centralizer which enables well tubular members to be run into rugose and/or ledged well bores.

It is a yet still further object of the invention to provide a stand-off band for use with a centralizer, or stop collar, or both together, or by itself, which enables well tubular members to be run into rugose and/or ledged well bores.

It is a yet still further object of the invention to provide a stop collar for use with a centralizer, or stand-off band or both together, or by itself, which enables well tubular members to be run into rugose and/or ledged well bores.

Each object above is to be read disjunctively with the object of at least providing the public with a useful choice.

The present invention aims to overcome, or at least alleviate, some or all of the afore-mentioned problems.

Further objects and advantages of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing the preferred embodiment of the invention without placing limitations thereon.

The background discussion (including any potential prior art) is not to be taken as an admission of the common general knowledge.

SUMMARY OF THE INVENTION

In a first aspect, the invention may broadly be said to consist in a centralizer for well bore holes, comprising a ring-shaped main body having an inner surface and an outer surface, a plurality of wide ridges extending radially outwards from the main body and axially along the outer surface, the ridges having at least one recess extending into the ridge from the inner surface, each recess having at least one longitudinal vane.

Preferably each of the vane or vanes extends radially inwards from the inner surface of the hollow ridge and has an inner edge aligned with a circumferential line that follows the circumference of the inner surface.

Preferably each of the vane or vanes is overall longitudinally aligned with the axis of rotation.

Alternatively each of the vane or vanes are helically spiralled around the centralizer.

Preferably a vane runs substantially the length of the ridge, bisecting the ridge.

Alternatively two vanes run substantially the length of the ridge, located at substantially equally spaced intervals across the ridge so as to divide the ridge into three roughly equal portions internally.

Alternatively three vanes run substantially the length of the ridge, located at substantially equally spaced intervals across the ridge so as to divide the ridge into four roughly equal portions internally.

Preferably the ridges curve or taper downwards at each open end of the centralizer to meet or blend with the outer surface substantially at the open ends. Preferably there are at least four and preferably twelve ridges spaced equidistant from one another around the outer surface of the centralizer.

Preferably there are at least four and most preferably twelve blades spaced equidistant from one another around the outer surface of the centralizer.

Preferably the centralizer has a flush mounted grease nipple. Preferably the centralizer is fitted with rubber or elastomer seals.

Preferably the seal is arranged to fit inside the centraliser.

Preferably the centralizer has a groove at one end into which the seal locates.

In a second aspect, the invention may broadly be said to consist in a centralizer for well bore holes, comprising:

a ring-shaped main body having an inner surface and an outer surface, with a central axis of rotation that passes through the open or hollow centre of the ring from a first open end to a second open end, and a plurality of elongate blades extending axially along the outer surface, each blade forming a wave form with at least two peaks and troughs along the length of the blade.

Preferably the wave form is sinusoidal.

Preferably each blade is formed from a web that extends radially outwards from the main body of the centralizer, and a flange that extends perpendicularly outward from each side of the outer end of the web across the top of the web.

Preferably the blades are overall aligned with the axis of rotation.

Alternatively wherein the blades are helically spiralled around the centralizer.

Preferably both the web and the flange have the form of a wave.

Alternatively the web has the form of a wave and the flange is straight-sided.

Preferably each of the blades runs along the outer surface of the central body of the centralizer from close to or at the first end, to close to or at the second end.

Preferably the blades curve concavely inwards towards the outer surface of the main body and merge with the surface close to or at the open end. Preferably the merge occurs substantially where the wave is axially aligned with the central axis of the centralizer.

Alternatively the wave form is substantially square.

Alternatively the wave form is substantially triangular.

Alternatively the wave form is linear, aligned axially with the central axis of the centralizer and having a series of spike wave peaks extending outwards perpendicularly from the main body of the web, and perpendicular to the axis of rotation, around the circumference of the main body of the centralizer.

Preferably there are at least four and preferably twelve blades spaced equidistant from one another around the outer surface of the centralizer.

Preferably the centralizer has a flush mounted grease nipple.

Preferably the centralizer is fitted with rubber or elastomer seals.

Preferably the seal is arranged to fit inside the centraliser.

Alternatively the centralizer has a groove at one end into which the seal locates.

In a third aspect, the invention may broadly be said to consist in a stand-off band for well bore holes, comprising:

a generally cylindrical hollow main body having an inner surface, an outer surface, a first end and a second end, and a plurality of wide, straight ridges extending radially outwards from a portion of the outer surface, equi-spaced around the main body, the main body having a first part with the inner surface substantially parallel to the outer surface, and a second part that is tapered in profile.

Preferably the outer end of the first part is squared off. Preferably the taper comes to a point. Preferably the taper is straight.

Preferably the ridges are located on the first part, extending radially outwards.

Preferably each ridge has an upper surface that follows the circumferential line of a circle that passes around the tops of all the blades.

Preferably each ridge is at least twice as wide (circumferential width) as its height (distance to which it extends from the surface of the main body).

Preferably the blades are shaped to present a smooth outer surface with no sharp corners or angles.

Preferably that end of the blades which is towards the tapered end tapers downwards substantially parallel to the taper of the second end, the outer end of the taper of each of the blades located substantially at or close to the inner end of the tapered portion of the stand-off band.

Preferably the inner surface of the main body of the stand-off band forms an inner circumferential surface, the inside of each of the ridges bulging or extending outwards from this surface to form a hollow pocket between the inner surface of the ridge and the circumferential surface.

Preferably a series of eyelet holes are formed passing through the main body circumferentially, the holes located midway between each of the ridges, and axially towards the first end. Preferably the outside surface of the ridges of the stand-off band are coated with an extreme pressure friction and abrasion-reducing product.

Preferably the extreme pressure friction and abrasion-reducing product is Molybdenum Disulfide.

Alternatively the extreme pressure friction and abrasion-reducing product is Diamond particle.

Alternatively the extreme pressure friction and abrasion-reducing product is an epoxy resin coating.

Preferably the holes are threaded and peened from the outside to prevent the accidental egress of screws installed in the holes.

Preferably the stand-off band is provided with a recess for an RFID tag.

In a fourth aspect the invention may broadly be said to consist in a stop collar for well bore holes, having a generally cylindrical hollow main body with an inner surface, an outer surface and first and second ends, the main body formed from a first part that extends inwards from the first end and which has parallel walls, and a second part that extends inwards from the second end to meet the first part and which is tapered in profile, the outer surface of the second part tapering down to meet the inside surface, the taper having a first portion furthest from the second end that has a first angle between the inner surface and the outer surface, and a second portion closest to the second end with a greater angle between the first portion and the axis of rotation of the main body.

Preferably the first end is squared off, a circumferential ridge extending from the first end parallel to the axis of rotation of the stop collar, circumferentially around the edge of the first end, to form a recess. Preferably a plurality of threaded holes are formed in the first portion towards the first end, spaced equally around the circumference, the outermost portion of each threaded hole peened.

In a fifth aspect, the invention may broadly be said to consist in a set of cast inserts shaped so as to be a complementary fit with the recess or recesses of the centralizer as described in any one of the appropriate statements above.

In a sixth aspect, the invention may broadly be said to consist in a set of cast inserts shaped so as to be a complementary fit with the recess or recesses of the stand-off band as described in any one of the appropriate statements above.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1a shows a typical prior art centraliser with straight blades aligned axially along the body of the centralizer.

Figure 1 b shows a typical prior art centraliser with blades helically angled around the body of the centralizer.

Figure 2 shows a typical casing running slack-off weight chart wherein the theoretical running weight in a cased hole is predicted, but in actual drill open hole conditions becomes erratic such that due to wellbore conditions the casing will not even run.

Figure 3 depicts a common down-hole situation wherein the slide-drilled hole diameter may close to the diameter of the drill bit while the hole drilled with a bent-housing rotary assembly drills a hole that is somewhat larger in diameter. The resultant variation in hole diameter results in down-hole ledges which may cause the square end of casing couplings to get hung up on the ledged well bore. Figure 4 shows a typical bending induced normal force Tornado plot of the forces experienced when running large diameter casing into a tortuous well bore, lines 1-3 representing relative forces, line 1 showing the restoration force of an API 10D bow spring centralizer, line 2 showing the rated maximum side load of the strongest currently available rigid body centralizer and line 3 the maximum side load the equipment of the present invention is capable of withstanding relative to the forces represented by lines 1 and 2.

Figure 5 shows a perspective view of a first embodiment of centralizer of the present invention, having a circular hollow main body with a central axis of rotation, and flat-topped wide ridges which extend radially outwards from the axis of rotation, and which also extend axially along the outer surface of the centralizer parallel to the axis of rotation, the ridges hollow and opening onto the inner surface, a longitudinally aligned blade or blades extending radially inwards from the pocket.

Figure 6a shows a side-on view of the centralizer shown in Figure 5, with a section line AA shown passing through the centralizer perpendicular to the axis of rotation and substantially bisecting the centralizer.

Figures 6b and 6c show two alternate close-up views of one of the flat-topped wide ridges taken along the section line AA, figure 6b showing a variant where three vanes extending radially inwards from the inner surface of the pocket to a circumferential line defined by the inner surface of the main body, figure 6c showing a variant where two vanes extend radially inwards from the inner surface of the pocket to the circumferential line defined by the inner surface of the main body.

Figure 7a shows a perspective view of a first embodiment of centralizer of the present invention, having blades which extend axially along the outer surface of the centralizer, the blades curved or waved along their length to form a waveform pattern, the centralizer having a fitting located substantially at a balance position so that a temporary lifting eye can be fitted to assist with installation. Figures 7b and 7c show end and side views, respectively, of the second embodiment of centralizer shown in figure 7a.

Figure 8 shows a close-up cross-section through the centralizer of figure 7a, showing detail of one of the blades in cross-section.

Figures 9a to 9d show alternative embodiments of blades, the figures showing the length of a single blade as it would appear if viewed looking radially inwards towards the central axis of the centralizer.

Figure 10 shows a cross-sectional view from and through the side of the centralizer, showing a temporary lifting eye fitted in the fitting of figure 5a or 7a.

Figure 11 shows a perspective view of a stand-off band according to an embodiment of the present invention.

Figure 12 shows a perspective view of a stop collar according to an embodiment of the present invention, the stop collar formed as a hollow ring.

Figure 13 shows a cutaway side view of one side of the hollow ring of the stop collar of Figure 12.

Figure 14 shows a cutaway view of the first embodiment of centralizer of the present invention, showing a cross-section though a portion of the main body and one of the ridges, the hollow internal centre or pocket of the ridge having a single vane extending radially inwards and bisecting the pocket, cast inserts located into the spaces each side of the vane to prevent fluid being trapped in the pockets in use, a grease nipple also shown to allow for a liquid or semi-liquid lubricant such as grease to be injected into the small void between the inside diameter of the centralizer and the outside diameter of the tubular.

Figure 15a shows a first form of seal arrangement designed to contain lubricant within a centralizer. Figure 15b shows a second form of seal arrangement designed to contain lubricant within a centralizer.

Figure 16 shows the centralizer of Figure 5 with an RFID tag installed into a purpose-cast recess.

Figure 17 shows a section of casing with the stop collar of the present invention installed on the downstream side of the casing coupling to aid running casing in situations where there are ledges in the well bore.

Figure 18 shows a section of casing with a stop collar and centralizer installed on the downstream side of the casing coupling to aid running casing into the well bore and facilitate casing rotation if desired.

Figure 19 shows a stop collar fitted above the casing coupling on the opposite side to a stand-off band.

Figure 20 shows a section of casing with a stop collar installed on both side of the casing coupling to aid running or retrieving casing in situations where there are ledges in the well bore.

Figure 21 shows a side cutaway view of a number of solid body type centralizers, each of substantially equal length, each having a different diameter such that a group can be nested one inside the other on a pallet or similar, and covered with a flat wooden or plastic cover to constrain their movement for safe transported.

Figure 22 shows an end view of a portion of the centralizer of Figure 5, the outside radius of the blades matched to suit that of the internal diameter of the well bore (either by choice of size or machining). DETAILED DESCRIPTION OF THE INVENTION

There are three main components to the centralisation system of the present invention. These are: a centraliser, a stand-off band, and a stop collar. The preferred embodiment for each of these components is described in detail in the relevant subsections below.

CENTRALISER

Centraliser - first embodiment

A first embodiment of centralizer 1 according to the present invention is shown in Figure 5. The centralizer 1 has a circular hollow or ring-shaped main body 2, having wide ridges 3 which extend radially outwards from the main body, and which also extend axially along the outer surface of the centralizer. The ridges 3 curve or taper downwards at each end of the centralizer 1 to meet or blend with the outer surface 5 substantially at the open ends of the centralizer 1. The ridges 3 are hollow along their length, closed from the outer surface 5, and open onto the inner surface 4 of the main body so that they have the form of pockets on the inner surface 4. Each ridge 3 has at least one vane 6, longitudinally aligned with the pocket and the axis of rotation, and running substantially the length of the ridge, bisecting the ridge. As shown in Figure 6, the vane or vanes extend radially inwards from the inner surface of the hollow ridge 3, the inner edge 7 of the vane aligned with a circumferential line that follows the circumference of the inner surface 4, so that in use, the inner edge of the vane(s) and the inner surface 4 are located against the outer surface of a cylindrical drill string or similar. The ridges are also curved across their tops from side to side, the curve following a circumferential line around the tops of all of the ridges around the centralizer 1.

The vanes described above are longitudinally aligned, but could also be spiralled or helical in relation

the main body of the centralizer. That is, for the preferred form described above, the overall or whole body of the vane is aligned with the axis of rotation, extending outwards radially. The vanes could also be spiralled helically around the outside surface of the centralizer, extending outwards radially at any one point, but overall spiralled around the outer surface.

To aid installation and reduce the risk of injury to personnel, a threaded hole 8 is provided on the centre of gravity of the centralizer, to allow the attachment of a lifting eye 113 or similar as shown in figure 10. Additionally, a temporary set- screw is provided in the centralizer to hold it on station whilst the tubular is being hoisted up to the Rig floor.

Centraliser - second embodiment

Figures 7a, 7b, and 7c show a second embodiment of the rigid or solid body centralizer 100 of the present invention. The centralizer 100 has a central body having the overall form of a hollow circular ring, with a central axis of rotation that passes through the open or hollow centre of the ring from a first open end to a second open end. A number of elongate blades 102 extend radially outwards from the outer surface of the central body, each of the blades 102 running along the outer surface of the central body of the centralizer from close to or at the first end, to close to or at the second end. A plurality of the blades 102 are spaced equidistant from one another around the circumference of the main body, roughly in the same numbers or positions as numerals around a clock face.

Each blade is formed so as to appear as a T-section in cross-section, the cross- section taken at any point along the length of the blade (except at the ends), typically as shown in figure 8. The upright (web 103 of the blade 102) of the T extends radially outwards from the main body of the centralizer, and the crossbar (flange 104) of the T extends perpendicularly from each side of the outer end or top of the upright. That is, across the top of the upright web 103.

Each web 103 extends from the first open end to the second open end of the main body. Each web 103 is formed so that it is curved or 'waved' along the length of the web, with at least two and preferably three or more peaks and troughs between the two ends. The wave form is substantially sinusoidal, or similar in form to a sinusoidal wave. The wave 'x-axis' is aligned substantially with the central axis of the centralizer. In a standard helical blade design such as is known in the art, the blade is angled to the axis of rotation or direction of travel of the centralizer, and thus presents a portion of its face to any ridges or similar in the well bore as it is run into the well bore. A drill string with spiral blade stabilizers will thus generate torque and exert a rotational force on the drill string as it is run into the well bore. Axially aligning the blades of a centralizer with the direction of travel or central axis of a centralizer overcomes this disadvantage but loses the advantage of being able to impart swirl or similar to poured concrete when a concrete sheath is poured around the centralizer. The centralizer of the present invention retains both advantages: the blades are pitched via the sinusoidal wave shape, but because each of the waves is relatively small compared to those of a traditional helically wound blade centralizer, the pressure on the faces is much less and less torque is developed. Also, the wave form is overall generally axially aligned, and therefore any torque effects are substantially reduced or cancelled out. As the blades 102 are generally axially aligned overall, the advantages of axially aligned blades are at least partly retained also. At each end 106, towards the open ends of the body, the crossbar of the T angles or curves concavely inwards/downwards towards the outer surface of the main body, the upright merging with the surface close to or at the open end. That is, each end of each of the blades 102 is concavely curved downwards towards the main body, curving outwards at the end parallel with the main body at or close to the end.

It is preferred that the wave of the blade 102 is shaped and formed so that this merging occurs substantially at a point on the wave where the wave is axially aligned with the central axis of the centralizer. Curving or flattening down the ends has the advantage that a gradual lead is presented to ledges. In the preferred embodiment the waves at the ends are presented at their neutral or mid-point so that any ledges or ridges are encountered generally perpendicularly, and thus hanging on ledges is reduced. It is preferred that the flanges (the crossbar of the T) are sinusoidal, but alternatively, these could be straight, with only the web sinusoidal. This however is not preferred, as it can add axial compressive stiffness which makes stress balancing less easy. Also, high bending stress in the radial load case may be exhibited in this configuration where the cantilever overhang is the largest. This configuration also adds weight, cost and pressure drop. Therefore it is most preferred that both the webs 3 and the flanges 4 are curved.

In alternative embodiments, the webs can be formed having waveform shapes other than sinusoidal. Examples are shown in figures 9a, 9b, 9c, and 9d. Figure 9a shows a square waveform, with rounded outer corners 107 and square inner corners 108.

Figure 9c shows a triangular waveform, with rounded corners 109, 10 on the peaks and troughs respectively. Figure 9d shows a generally linear blade 111 , aligned axially with the central axis of the centralizer, the blade 111 having a series of 'spiked' wave peaks 112 extending outwards perpendicularly from the main body of the web, and perpendicular to the axis of rotation, around the circumference of the main body of the centralizer.

The same as for the preferred embodiment, each of the blades shown in figures 9a - 9d has two or more waves (a peak/trough pair) along its length. The blade shown on the web in figure 9b is substantially the same as that described for the preferred embodiment above, but has three peak/trough pairs along its length. Similarly, the square and triangular waved blades in figures 9a and 9c have three peak/trough pairs, and there are three spikes in the wave form of the blade shown in figure 9d.

The configuration of the blades as described above allows the centralizer to slide inside the well bore with the minimum of damage to the filter cake but also generating swirl, thereby enhancing the quality of the cement sheath when circulated. The total flow area is also as large as practicable, in order to reduce differential pressure across the tools when cementing.

The T-section shape of the rib also provides a very low differential pressure across the tool, thereby reducing the equivalent circulating density of flowing fluids and further aiding hole cleaning and cementing. It also provides exceptionally high axial compressive load capability such that the casing can be run with Side Door Elevator casing running equipment installed up against the centralizer thus reducing Rig time and cost.

Although the preferred forms of blades described above are arranged aligned with the axis of the centralizer, these could also be spiralled or arranged helically around the main body of the centralizer. That is, for the preferred form, the blades overall extend outwards radially. However, the blades could also extend outwards radially at any particular point, but rather than having their entire length aligned with the axis of rotation; they are also spiralled helically around the outside surface of the centralizer. . The vane or vanes in the pockets are longitudinally aligned with the axis of the pocket, That is, along the length of the pocket, but spiralled helically with the pocket in this embodiment.

The centralizers described above, are designed to be cast in ferrous metal using a green sand, resin sand, hard sand or investment cast process. Alternatively, they can be forged or fabricated in a ferrous metal.

In applications where it may be desired to reduce axial drag, the outside surface of the webs or blades of the centralizer may be coated with a suitable extreme pressure friction and abrasion-reducing product solid lubricant such as Molybdenum Disulfide or Diamond particle. A protective coating such as an epoxy resin may also be used if required, to encapsulate the solid lubricant.

To aid installation and reduce the risk of injury to personnel, a threaded hole 109 is provided on the centre of gravity of the centralizer, to allow the attachment of a lifting eye 113 or similar. Additionally, a temporary set-screw is provided in the centralizer to hold it on station whilst the tubular is being hoisted up to the rig floor.

For both embodiments described above, the outside radius of the blades suits that of the internal diameter of the well bore (either by choice of size or machining), as shown in Figure 22. This reduces the tendency for the blades to "dig-in" and damage filter cake which might otherwise create fluid losses and/or differential sticking issues. Stand-off band

The stand-off band is a stand-alone part of the centralization system of the present invention. The stand-off band will typically be run without the centralizer or the stop collar, typically abutting one side of a casing coupling as shown in Figure 17, or both sides. In some instances however, a stop collar may be fitted above the casing coupling opposite to the stand-off band, as shown in Figure 19, to aid withdrawing the tubular should there be a requirement to do so.

A preferred embodiment of stand-off band 200 is shown in figure 1 1. The standoff band 200 has a generally cylindrical hollow main body 201 having an inner surface, an outer surface 206 and two ends - a first end 204 and a second end 205. A plurality of wide, straight ridges 202 extend outwards from the outer surface 206, equi-spaced around the main body 201 , and extending radially outwards. In side profile (that is, looking radially inwards directly towards the axis of rotation), the main body of the stand-off band can be divided into two parts by a plane perpendicular to the axis of rotation. The first part, from the first end inwards to the substantially central dividing plane, has parallel walls (the inner surfaces and outer surface are aligned substantially parallel to one another), with the stand-off band 200 squared off at the first end 204. The second part, outwards from the plane to the second end 205, is tapered in profile. The outside surface of the second end tapers down to meet the inside surface - that is, it tapers down to a point. The taper is straight. The taper can also be curved.

The ridges 202 are located on the first part. Each of the ridges 202 extends radially outwards from the main body of the stand-off band. Each ridge is wide and has an upper surface that follows the circumferential line of a circle that passes around the tops of all the ridges 202. That is, curving inwards slightly from flat. Each ridge 202 is at least twice as wide (circumferential width) as its height (distance to which it extends from the surface of the main body). The ridges 202 are shaped so as to have, or to present, a smooth outer surface with no sharp corners or angles. The upper corners where the side walls of the ridges meet the upper outer surface or top 203 are blended or radiused. The lower corners where the side walls of the ridges meet the main body are also blended or radiused. That end of the ridges which is towards the second, tapered end tapers downwards substantially parallel to the taper of the second end, the outer end of the taper of each of the ridges located substantially at or close to the inner end of the second part.

The inner surface of the main body of the stand-off band forms a broken inner circumferential line. The inside of each of the ridges bulges or extends outwards from this inner circumference to form a hollow pocket between the inner surface of the ridge and the line of the inner circumference, and thus break the inner circumferential line. A series of eyelet holes 209 or similar are formed passing through the main body circumferentially midway between each of the ridges, and axially towards the first end 204.

The purpose-designed ridge-riding profile of the stand-off band enables it to be used even with large diameter tubulars wherein well bore tortuosity, resulting in high bending induced normal forces, may render currently available systems inadequate.

The wide, straight ridges of the stand-off band allow it to slide inside the well bore with the minimum of damage to the filter cake, thereby reducing the risk of differential sticking. The design also has a total flow area that is as large as practicable, in order to reduce differential pressure across the tools when cementing.

In applications wherein it may be desired to reduce axial drag, the outside surface of the ridges of the stand-off band may be coated with a suitable extreme pressure friction and abrasion-reducing solid lubricant product such as Molybdenum Disulfide or Diamond particle. A protective coating such as an epoxy resin may also be used to encapsulate the solid lubricant.

Similarly to the centralizer embodiments described above, the outside radius of the ridges suit that of the internal diameter of the well bore. This reduces the tendency for the ridges to "dig-in" and damage filter cake which might otherwise create fluid losses and/or differential sticking issues. The outside radius of the ridges suits that of the internal diameter of the well bore (either by choice of size or machining). This reduces the tendency for the ridges to "dig-in" and damage filter cake which might otherwise create fluid losses and/or differential sticking issues.

The stand-off band described above is designed to be cast in ferrous metal using a green sand, resin sand, hard sand or investment cast process. Alternatively, it can be forged or fabricated in a ferrous metal.

Stop Collar

A preferred embodiment of stop collar 300 is shown in figures 12 and 13. The stop collar 300 has a generally cylindrical hollow main body 301 having an inner surface, an outer surface 306 and two ends - a first end 304 and a second end 305. In side profile as shown in Figure 13 (that is, looking radially inwards directly towards the axis of rotation), the main body of the stop collar can be divided into two parts by a plane 307 perpendicular to the axis of rotation. The first part, from the first end inwards to the substantially central dividing plane, has parallel walls (the inner surfaces and outer surface are aligned substantially parallel to one another), with the stop collar 300 squared off at the first end 304. A circumferential ridge 308 extends from the first end parallel to the axis of rotation of the stop collar, circumferentially around the edge of the first end, to form a recess into which the end of centralizer fits in use, the recess intended to reduce the egress of torque reducing lubricant inside the centralizer.

The second part, outwards from the plane 307 to the second end 305, is tapered in profile, the second end tapering down to meet the inside surface - that is, it tapers down to a point. The taper can be divided into two portions - a first portion furthest from the second end 305 having a first angle between the inner surface and the outer surface, and a second portion closest to the second end with a greater, or less acute angle between the first portion and the plane 307.

A plurality of threaded holes 309 are formed passing through the main body circumferentially midway between each of the blades, and axially towards the first end 204. The threaded holes 309 are equally spaced around the circumference of the stop collar. In the preferred embodiment, there are six holes.

The outermost portion of each threaded hole is peened. All permanent screws on the equipment are of a specific length such that when installed into the threaded holes 306, and in the event that they should work loose, the purpose- peened thread prevents the screw from coming right out, thus averting the risk of junk in the well.

The ridge-riding profile of the stop collar, when used in combination with the ultra high strength centralizer, enables the system to be used even with large diameter tubulars wherein well bore tortuosity, resulting in high bending induced normal forces, may render currently available systems inadequate.

To aid installation and reduce the risk of injury to personnel, a lifting eye and threaded hole is provided on the centre of gravity of the stop collar. The stop collar can be cast in ferrous metal using a green sand, resin sand, hard sand or investment cast process, or forged or fabricated in a ferrous metal.

A stop collar provided with a purpose formed recess into which a Radio Frequency Identification (RFID) tag may be fitted. Said RFID tag would be loaded off-line with casing particulars and this information retrieved with a scanner on the Rig floor and as the tubulars are run, thereby providing accurate and time/cost saving benefits. The RFID tag may also provide down-hole depth reference sensing, even after being cemented into the wellbore.

General

The stand-off band, stop collar and complimenting centralizer enable well tubular members to be run into rugose and/or ledged well bores. The centralizer and stop collar tools may be run together or separately. The stop collar by itself provides improved ridge-dodging for one or both sides of the casing couplings. The purpose-designed ridge-riding profile of the stand-off band enables it to be used even with large diameter tubulars wherein well bore tortuosity, resulting in high bending induced normal forces, may render currently available systems inadequate.

The centralization system may be used for casing, liner and drilling with casing or drilling with liner applications or any other well construction tubular use wherein the features described would provide benefits.

Each of the components of the centralizing system are preferably cast but may also be forged or fabricated using metals that have the required strength but which are also suitable for milling or drilling using standard drilling equipment. A medium-carbon steel such as AISI 4140 is preferred while the preferred method of manufacture is investment cast using either the lost wax or lost foam method.

To facilitate future well sidetracking options, all materials used should most preferably be capable of being either milled and/or drilled using standard equipment.

The stand-off band, stop collar and centralizer are all designed using Finite Element Analysis methods, to ensure that they are able to withstand the exceptionally high bending induced loads that such equipment may see when running large diameter tubulars into a tortuous wellbore. Such loads are approximately three times that of currently available slip-on rigid type centralizers and up to eighty times that of API 10D bow spring centralizers.

The centralizer is also designed using Finite Element Analysis methods to ensure that it has adequate axial compressive strength to enable the casing running elevators to be installed directly onto the centralizer, thus saving Rig time and reduced risk on the Rig floor.

In applications wherein high down-hole temperatures are anticipated such that trapped fluid may result in the collapse of a tubular due to the pressure build-up, the centralization system is provided with cast inserts designed to prevent said trapped fluid. These are shown as inserts 20 on figure 14. These cast inserts completely fit, or form a complementary fit with each of the recesses in which they are fitted to prevent fluid build-up in the recess. These are provided particularly for the first embodiment of the centralizer, and the stand-off band, but may also be provided for any embodiment having recesses or pockets on the inner surface, where a smooth inner surface is required, that will sit flush with, and follow, the outer surface of a string or similar. Therefore the inserts sit in the recesses or pockets and form a flush surface together with the main body.

In applications wherein it is desired to rotate the casing or liner string to either land the casing and/or enhance cement sheath quality, provision is made on the centralizer for a liquid or semi-liquid lubricant such as grease to be injected into the small void between the inside diameter of the centralizer and the outside diameter of the tubular. For example, the first form of centralizer has at least one grease nipple 21 , located in the angle between the base of a ridge 3 and the outer surface 5. The grease nipple is preferably flush mounted to provide the mechanism by which the centralizer-tubular interface is lubricated in situ, preferably with a high temperature, water resistant and high film strength heavy oil or grease. The lubricant provides 30 - 70% torque reduction even at very high side loads, thereby assisting with running the tubulars. The ability to rotate the casing while cementing may also enhance the cement sheath quality.

This lubricant shall preferably have good water resistance, a high boiling temperature and may have its film strength enhanced as desired with an extreme pressure additive such as PowerUp, Molybdenum Disulfide, Diamond particles or similar product. To prevent the egress of lubricant, the centralizer may or may be fitted with rubber or elastomer seals. The seal may be arranged to fit inside the centraliser, such as the lip seal 50 as shown in Figure 15a. Alternatively, the lip seal may be arranged to locate into a groove at the end of the centralizer, such as the seal 51 shown in Figure 15b, thereby making it easier to fit the larger diameter seals over the casing.

To enhance the functionality of the equipment, for any given application, the stand-off band, centralizer or the stop collar would have provision for a Radio Frequency Identification (RFID) tag to be installed into a purpose-cast recess. An example is shown in Figure 16, the RFID tag 22 shown located in a recess on the outer surface of the first form of centralizer. The RFID tag would be loaded off-line with information pertaining to the casing including, but not necessarily limited to tally length, casing heat number and any other information deemed to be of value. The RFID tag would be read with a scanner on the Rig floor as the tubulars are run, thereby providing accurate and time/cost saving benefits. The RFID tag may also provide down-hole depth reference sensing, even after being cemented into the wellbore.

Solid body type centralizers are very bulky such that they are expensive to ship. They are typically of varying length such that if smaller tools are nested inside larger tools, the former are not constrained and will move and may cause damage whilst in transit. Figure 21 shows a number of solid body type centralizers, each of substantially equal length, each having a different diameter such that a group can be nested one inside the other on a pallet or similar, and covered with a flat wooden or plastic cover to constrain their movement for safe transported.

Claims

CLAIMS:

1. A centralizer for well bore holes, comprising a ring-shaped main body having an inner surface and an outer surface, a plurality of wide ridges extending radially outwards from the main body and axially along the outer surface, the ridges having at least one recess extending into the ridge from the inner surface, each recess having at least one longitudinal vane.

2. A centralizer as claimed in claim 1 wherein each of the vane or vanes extends radially inwards from the inner surface of the hollow ridge and has an inner edge aligned with a circumferential line that follows the circumference of the inner surface.

3. A centralizer as claimed in claim 1 or claim 2 wherein each of the ridges and vane or vanes is overall longitudinally aligned with the axis of rotation.

4. A centralizer as claimed in claim 1 or claim 2 wherein each of the ridges and vane or vanes are helically spiralled around the centralizer.

5. A centralizer as claimed in any one of claims 1 to 4 wherein the vane or vanes run substantially the length of the ridge, bisecting the ridge.

6. A centralizer as claimed in any one of claims 1 to 4 wherein two vanes run substantially the length of the ridge, located at substantially equally spaced intervals across the ridge so as to divide the ridge into three roughly equal portions internally.

7. A centralizer as claimed in any one of claims 1 to 4 wherein three vanes run substantially the length of the ridge, located at substantially equally spaced intervals across the ridge so as to divide the ridge into four roughly equal portions internally.

8. A centralizer as claimed in any one of claims 1 to 7 wherein the ridges curve or taper downwards at each open end of the centralizer to meet or blend with the outer surface substantially at the open ends.

9. A centralizer as claimed in any one of claims 1 to 8 wherein there are at least four and preferably twelve ridges spaced equidistant from one another around the outer surface of the centralizer.

10. A centralizer as claimed in any one of claims 1 to 9 wherein there are at least four and preferably twelve blades spaced equidistant from one another around the outer surface of the centralizer.

11. A centralizer as claimed in any one of claims 1 to 10 wherein the centralizer has a flush mounted grease nipple.

12. A centralizer as claimed in any one of claims 1 to 11 wherein the centralizer is fitted with rubber or elastomer seals.

13. A centralizer as claimed in claim 12 wherein the seal is arranged to fit inside the centraliser.

14. A centralizer as claimed in claim 12 wherein the centralizer has a groove at one end into which the seal locates.

15. A centralizer for well bore holes, comprising a ring-shaped main body having an inner surface and an outer surface, with a central axis of rotation that passes through the open or hollow centre of the ring from a first open end to a second open end, and a plurality of elongate blades extending from the outer surface, each blade forming a wave form with at least two peaks and troughs along the length of the blade.

16. A centralizer as claimed in claim 15 wherein the blades are overall aligned with the axis of rotation.

17. A centralizer as claimed in claim 15 wherein the blades are helically spiralled around the centralizer. 8. A centralizer as claimed in any one of claims 15 to 17 wherein the wave form is sinusoidal.

19. A centralizer as claimed in any one of claims 15 to 18 wherein each blade is formed from a web that extends radially outwards from the main body of the centralizer, and a flange that extends perpendicularly outward from each side of the outer end of the web across the top of the web.

20. A centralizer as claimed in claim 19 wherein the web has the form of a wave and the flange is straight-sided.

21. A centralizer as claimed in claim 19 wherein both the web and the flange have the form of a wave.

22. A centralizer as claimed in any one of claims 15 to 21 wherein each of the blades runs along the outer surface of the central body of the centralizer from close to or at the first end, to close to or at the second end.

23. A centralizer as claimed in claim 22 wherein the blades curve concavely inwards towards the outer surface of the main body and merge with the surface close to or at the open end.

24. A centralizer as claimed in claim 23 wherein the merge occurs substantially where the wave is axially aligned with the central axis of the centralizer.

25. A centralizer as claimed in claim 15 wherein the wave form is substantially square.

26. A centralizer as claimed in claim 15 wherein the wave form is substantially triangular.

27. A centralizer as claimed in claim 15 wherein the wave form is linear, aligned axially with the central axis of the centralizer and having a series of spike wave peaks extending outwards perpendicularly from the main body of the web, and perpendicular to the axis of rotation, around the circumference of the main body of the centralizer.

28. A centralizer as claimed in any one of claims 15 to 27 wherein there are at least four and preferably twelve blades spaced equidistant from one another around the outer surface of the centralizer.

29. A centralizer as claimed in any one of claims 15 to 28 wherein the centralizer has a flush mounted grease nipple.

30. A centralizer as claimed in any one of claims 15 to 29 wherein the centralizer is fitted with rubber or elastomer seals.

31. A centralizer as claimed in claim 30 wherein the seal is arranged to fit inside the centraliser.

32. A centralizer as claimed in claim 30 wherein the centralizer has a groove at one end into which the seal locates.

33. A stand-off band for well bore holes, comprising a generally cylindrical hollow main body having an inner surface, an outer surface, a first end and a second end, and a plurality of wide, straight ridges extending radially outwards from a portion of the outer surface, equi-spaced around the main body, the main body having a first part with the inner surface substantially parallel to the outer surface, and a second part that is tapered in profile.

34. A stand-off band as claimed in claim 33 wherein the outer end of the first part is squared off.

35. A stand-off band as claimed in claim 33 or claim 34 wherein the taper comes to a point.

36. A stand-off band as claimed in any one of claims 33 to 35 wherein the taper is straight.

37. A stand-off band as claimed in any one of claims 33 to 36 wherein the ridges are located on the first part, extending radially outwards.

38. A stand-off band as claimed in any one of claims 33 to 37 wherein each ridge has an upper surface that follows the circumferential line of a circle that passes around the tops of all the blades.

39. A stand-off band as claimed in any one of claims 33 to 38 wherein each ridge is at least twice as wide (circumferential width) as its height (distance to which it extends from the surface of the main body).

40. A stand-off band as claimed in any one of claims 33 to 39 wherein the blades are shaped to present a smooth outer surface with no sharp corners or angles.

41. A stand-off band as claimed in any one of claims 33 to 40 wherein that end of the blades which is towards the tapered end tapers downwards substantially parallel to the taper of the second end, the outer end of the taper of each of the blades located substantially at or close to the inner end of the tapered portion of the stand-off band.

42. A stand-off band as claimed in any one of claims 33 to 41 wherein the inner surface of the main body of the stand-off band forms an inner circumferential surface, the inside of each of the ridges bulging or extending outwards from this surface to form a hollow pocket between the inner surface of the ridge and the circumferential surface.

43. A stand-off band as claimed in any one of claims 33 to 42 wherein a series of eyelet holes are formed passing through the main body circumferentially, the holes located midway between each of the ridges, and axially towards the first end.

44. A stand-off band as claimed in any one of claims 33 to 43 wherein the outside surface of the ridges of the stand-off band are coated with an extreme pressure friction and abrasion-reducing product.

45. A stand-off band as claimed in claim 44 wherein the extreme pressure friction and abrasion-reducing product is Molybdenum Disulfide.

46. A stand-off band as claimed in claim 44 wherein the extreme pressure friction and abrasion-reducing product is Diamond particle.

47. A stand-off band as claimed in claim 44 wherein the extreme pressure friction and abrasion-reducing product is an epoxy resin coating.

48. A stand-off band as claimed in any one of claims 43 to 47 wherein the holes are threaded and peened from the outside to prevent the accidental egress of screws installed in the holes.

49. A stand-off band as claimed in any one of claims 33 to 48 wherein the standoff band is provided with a recess for an RFID tag.

50. A stop collar for well bore holes, having a generally cylindrical hollow main body with an inner surface, an outer surface and first and second ends, the main body formed from a first part that extends inwards from the first end and which has parallel walls, and a second part that extends inwards from the second end to meet the first part and which is tapered in profile, the outer surface of the second part tapering down to meet the inside surface, the taper having a first portion furthest from the second end that has a first angle between the inner surface and the outer surface, and a second portion closest to the second end with a greater angle between the first portion and the axis of rotation of the main body.

51. A stop collar as claimed in claim 50 wherein the first end is squared off, a circumferential ridge extending from the first end parallel to the axis of rotation of the stop collar, circumferentially around the edge of the first end, to form a recess.

52. A stop collar as claimed in claim 50 or claim 51 wherein a plurality of threaded holes are formed in the first portion towards the first end, spaced equally around the circumference, the outermost portion of each threaded hole peened.

53. A set of cast inserts shaped so as to be a complementary fit with the recess or recesses of any one of claims 1 to 14, the inserts having an inner surface that sits flush with, and follows, the inner surface of the main body.

54. A set of cast inserts shaped so as to be a complementary fit with the recess or recesses of any one of claims 42 to 49, the inserts having an inner surface that sits flush with, and follows, the inner surface of the main body.