WO1993012322A1

WO1993012322A1 - Packers

Info

Publication number: WO1993012322A1
Application number: PCT/GB1992/002293
Authority: WO
Inventors: Bertrand Pierre Marie Peltier; Colin Atkinson
Original assignee: Services Petroliers Schlumberger; Schlumberger Technology Corporation
Priority date: 1991-12-13
Filing date: 1992-12-10
Publication date: 1993-06-24
Also published as: GB2262553A; GB9126543D0; GB2262553B

Abstract

A packer in the form of an inflatable elongate elastic sleeve is commonly employed as a temporary plug to seal off part of an oil well borehole from the rest. To prevent the sleeve from rupturing, it is commonly provided with internal wire-like reinforcing elements. Such sleeves suffer from failures where the sleeve extrudes between adjacent wires, and ruptures. The invention suggests a solution where the deformability of the wire reinforced region of the sleeve and the deformability of the bulk material making up the rest of the sleeve are matched to one another. The deformabilities are matched so that the tendency for the wires to de-bond is reduced. This is accomplished by modifying the nature of the material in the wire region, or the physical structure of the material, or by modifying the nature of the wires themselves.

Description

Packers

This invention relates to packers, and concerns in particular inflatable packers suitable for sealing the annulus of an oil well borehole.

Once a well, such as a hydrocarbon well like an oil well, has been drilled it may be desirable, or even necessary, to isolate one length of the well from another. For example, when an oil well has been drilled it is normal, after casing the entire length of the borehole with concrete, to seal off part of the borehole from the rest using a temporary plug known as a packer, and then to investigate the fluid that seeps from the surrounding rock formations into the borehole through holes made in the casing at specified depths secure in the knowledge that the fluid can only have come from the chosen length of borehole. Again, it may be desirable to pump chemicals of one sort or another into the formations, and the use of a correc ly-located packer ensures that the chemicals go only where they are needed.

Of course, once the packer has done its job - or, rather, once the job it permits has been completed - it must be removed (and possibly replaced elsewhere in the borehole). Accordingly, a packer should be easily removable, and desirably should be capable of re-use many times.

A well such aε an oil well - and hereinafter the invention is for convenience discussed with reference to oil wells only, though it may have use in other types of well - normally has a concrete-lined elongate borehole around 18 inches (45 cm) in diameter with 12 inch (30 cm) diameter tubular piping, referred to as a "string" of tubing, disposed co-axially therein to form an annular space (the "annulus", about 3 inches [7.5 cm] across at either side) therearound. So-called "mud" occupies the annular volume, and formation fluids and treatment fluids pass up and down the core of the string via whatever valves, sampling chambers and other mechanisms may be contained therein. In this type of situation the packer is a device that fits within the annulus and blocks it off, like a ring-shaped plug, so as to isolate the annular space above the packer from that below other than by way of the tubing string. The packer must be removable (and replaceable and re-usable) , and one particular form of packer much in favour these days is of an inflatable variety, being in concept little more than an elongate elastic sleeve around four to five feet (1.2 to 1.5 m) long wrapped around and attached (usually by way of some "floating", movable mechanism) at each of its ends to the tubing of the string, which sleeve can be inflated - pumped up - like a balloon by pumping thereinto some suitable fluid from within the string tubing. As the sleeve inflates so it expands, its outside diameter increasing, until eventually it comes into contact with the inner wall of the bore casing; if the internal pumping pressure is sufficient the sleeve is then pressed hard against that wall, and so sealingly blocks the annulus. Then, once its work is done, it can be deflated (by reducing the pressure of the fluid inside it) and either withdrawn from the borehole completely or moved to a different site within the hole and used again.

The forces within an inflated packer of this inflatable sleeve type - and hereinafter the term "packer" is used to mean such a variety unless specified otherwise - are considerable, but for the most part are balanced by the opposing forces exerted by the reaction of the borehole wall upon the sleeve. However, at either end, where the sleeve extends from the tubing outwards towards the borehole wall, the packer sleeve is unsupported, and will therefore be under considerable stress where the pressure difference between the inside and the outside is large (as it must be, at least at one end, if the sleeve is to inflate) . Indeed, this difference may be so large as to be beyond the unaided ability of the sleeve material to withstand, resulting in the sleeve expanding enormously at one or other end and, inevitably, rupturing - exploding like an over- inflated balloon. It is desirable, therefore, to provide the sleeve with some form of built-in support that will limit its expansion, and so prevent it rupturing under the expected pressure difference across it (usually of the order of 6000 lbs/sq in, or about 41 MPa), and to this end it has been common to provide the sleeve with internal reinforcing elements of a wire- or thread-like nature much like the similar reinforcing cords found in modern tyres.

The reinforcing elements tried so far have taken many different forms, and been made of many different types of material. In general, though, they have been wire-like - usually actually of metal wire, and so occasionally referred to hereinafter as "wires" - and laid as several layers of a multiplicity of generally parallel and contiguous (touching side to side) individual elements. In some versions all the individual wires are parallel, even with those in different layers, and run straight up and down (along a meridian of) the sleeve, but the sleeves made with such layers of reinforcing wires embedded in the basic "elastic" sleeve material suffer all too frequently from disastrous failures of the type where, as in use the sleeve expands, the sleeve extrudes between adjacent wires, and the sleeve material splits, and then ruptures, parallel to the wires. A different version provides the wires in two groups, the wires in each being parallel to each other but being at a small angle, of the order of 10* or so, to the wires in the other, the whole laid in the sleeve material so as to extend therealong with each group as either a right- or a left-hand helix. The angle of the wires might have been expected to provide some component of the reinforcing effect in a direction around the sleeve (as well as the main effect along the sleeve), and so prevent the sleeve splitting along its length, and while undoubtedly this has indeed been found nevertheless the sleeves still suffer from extrusion, splitting and concomitant rupture.

The present invention seeks to solve this same problem but in a quite different manner, one occasioned by a detailed study, and closer understanding, of the factors involved.

The general structure of a wire-reinforced sleeve is that of a set of reinforcing wires embedded within a thick sheet of elastic material (usually rubber). In practice the structure may in fact be a three-layer one, rather like an old-fashioned motorcar tyre, and having an inner inflation layer of elastic material (comparable to the inner tube of the tyre) with outside it a sequence of first a reinforcing layer (like the carcass of the tyre proper, with the reinforcing wires embedded in a thin matrix layer of elastic material) and second an outer sealing layer of more - and possibly different - elastic material (like the outer, or tread, part of the tyre). Although all three layers of the sleeve could well be integral, and actually formed integrally, it is most common for them to be formed separately, and then bonded together, by a vulcanising process, like a sandwich. An understanding, and appreciation, of the problem - and of the proposed solution, comes from a consideration of what happens to this structure as the sleeve expands.

Firstly, there is the mode of failure. What seems to happen is that, as the sleeve expands, the actual expansion is non-uniform around the sleeve, some parts of the sleeve expanding more than others (even in sleeves with crossing-over reinforcing threads), so that in some places there are large gaps between adjacent wires while in others there are none (or only small gaps). As a result, there is a tendency for the elastic material in the area of the larger gaps to expand preferentially - to be blown out, or extruded, through the gaps - and inevitably in those areas the material reaches its elastic limit, and further inflation causes it plasticly to deform, and eventually to rupture, and the sleeve to fail.

Secondly, there are the small scale changes that occur as the sleeve inflates. The forces needed to deform a body of an elastic substance are proportional to the deformation required, and are also proportional, but inversely so, to the original bulk of the body, and especially the dimension of the body in the deformation direction (the smaller the body the greater the applied force to result in any particular deformation). Now, in a wire-reinforced sleeve with contiguous wires the overall deformation - stretching - in a direction across the wires is determined by the much greater bulk of the elastic sleeve material either side of the wire layer(s). but since the deformation in that material ⁽a region devoid of wires) is inevitably much larger than the deformation in the material in the region between and immediately adjacent or actually in contact with the wires, because the effective length of that latter material is so much shorter (so it will not deform as much for the same applied force), there are generated substantial shear forces between the two regions of material. These shear forces rapidly build to a level at which the material is actually torn apart at or near the wire surface - the wires are thus de-bonded from the material surrounding them - and thus suddenly and unexpectedly deforms in one or two positions around the sleeve (relieving the load on the interwire material elsewhere) rather than gently and uniformly therearound. The resultant change in geometry - a relatively wide gap between two "adjacent" wires, and a small, or negligible, gap between the other adjacent wire pairs - means that any further inflationary forces appear to be • concentrated almost exclusively on the revealed weak point, whereupon the observed extrusion, rupture and failure becomes inevitable.

The surprisingly simple solution proposed by the present invention follows from the analysis of the problem. Clearly, the root of the problem lies in the different deformability of the sleeve in the area of the reinforcing wires, this difference resulting in the sleeve-destroying shear forces generated internally as the sleeve expands. And equally clearly the basis of the solution lies in the appreciation that, if that difference can be reduced, or even removed altogether, then there will be no generated shear forces, and the sleeve will inflate smoothly and uniformly. And the achievement of this desired end can be arranged either by modifying the nature of the material in the wire region, so that it has a different elasticity that causes its deformability to "match" that of the wire-free surrounding bulk material, or by modifying the physical structure of the elastic sleeve material in the wire region, so that, even with the same elasticity, it has the required matching deformability (or "compliance"), or by modifying the very nature of the wires themselves, so that taken as a whole the wire- filled region has the desired matching deformability.

In one aspect, therefore, the invention provides a packer of the wire-reinforced inflatable sleeve type, wherein the deformability of the region containing the wire reinforcing elements is matched to that of the bulk material making up the rest of the sleeve, so that, when the sleeve is elastically deformed, the tendency for the reinforcing elements to de-bond is reduced or even eliminated, and as a result the deformation is more uniform throughout the relevant part of the sleeve, and the reinforcing elements retain their equal spacing thereby minimizing the largest gap of unsupported sleeve material .

The invention relates to a packer of the wire- reinforced inflatable sleeve type. This type has already been briefly described hereinbefore; basically it takes the form of an elongate sleeve of some suitable elastic material wrapped around and attached (usually by way of a "floating", movable collar-like mechanism commonly referred to as a "shoe") at both of its ends to the tubing of the string. The sleeve can be inflated by pumping thereinto some suitable fluid from within the string tubing, and the sleeve has internal reinforcing elements of a wire-, thread- or cord-like nature which are embedded therein usually as several layers of a multiplicity of generally parallel individual elements. The elements can be in crossing groups, but preferably they are all parallel, even with those in different layers, and run straight up and down (along a meridian of) the sleeve, most preferably with a small but significant regular spacing between adjacent elements.

The materials and dimensions employed for the sleeve and the reinforcing elements can be any of those used or suggested for use in the Art. Thus, the sleeve is conveniently made of one or several polymers of various types (depending on temperature and chemical environment), typically an acrylonitrile butadiene polymer mixed with carbon black. It can have a length around one metre, its outside diameter being selected according to the diameter of the hole to be sealed. Common expansion ratios are from 1,25 to 2.0 (with extremes up to 3.0). For example, to seal a hole of 4 in (10 cm) internal diameter a sleeve of 2 to 3 in (5 to 7.5 cm) outside diameter would be selected and then inflated to 4 in.

The reinforcing elements are preferably made of a high-carbon steel wire (possibly copper or zinc coated) of around 0.02 in (0.5 mm) diameter but more generally (0.5 to 1 mm), or perhaps a natural or synthetic fibre (the latter made from a polymer such as KEVLAR [RTM] ) .

Because of the deformation of the sleeve it is best to have only one layer of reinforcement. If there are several layers - most present-day sleeve include several layers, possibly as many as five, to reduce the extrusion gaps between the wires - the external one takes most of the tension. In connection with the present invention it is recommended that the number of layers be limited to at most two. The reinforcing elements are disposed parallely side by side, but most preferably - in some embodiments, at least - they are not contiguous - that is, each does not actually touch its neighbours - but are slightly spaced one from the other. The actual spacing that is optimum depends upon a number of factors, including the nature of the reinforcing element itself (as will become clearer hereinafter), but it should not be so large that there is any significant risk of the elastic sleeve material being extruded by the applied pressure through the spaces. In general, it may be said that the spacing should be not greater than roughly the effective diameter/width of the reinforcing elements.

The inventive feature of the sleeve-type packer of the invention might be said to reside in the fact that the deformability of the region containing the reinforcing elements is matched to that of the bulk material making up the rest of the sleeve. There are several ways in which this can be achieved, these being notionally divisible into three main groups: one wherein the nature of material in the wire region is modified, or chosen, so that it has a different elasticity that gives it the needed deformability; one wherein the physical structure of the elastic sleeve material in the wire region is modified so that, even with the same elasticity, it has the required matching deformability; and one wherein the very nature of the wires themselves is modified, or chosen, so that taken as a whole the wire-filled region has the desired matching deformability. Each of these is now discussed in more detail.

One way to achieve matching deformability is suitably to modify, or choose, the nature of material in the wire region, so that it has an appropriately different elasticity from that of the bulk, wire-free material (one that gives it the required deformability). The need is for the wire-containing region to have a much higher elasticity, so that it can deform further, and more readily, despite the smaller effective dimensions of the material being deformed. This may be attained by making the wire-containing layer from a less-vulcanised (cross-linked) version of the material used for the bulk of the sleeve, or by using a foamed version of that bulk material (foamed elastomers commonly are far more elastic than their unfoamed analogues), or even by employing a completely different elastomeric material for the wire-containing layer.

Another way to achieve the required matching deformability is suitably to modify the actual physical structure of the elastic sleeve material in the wire region so that, even with the same elasticity, it has the required matching deformability. Becauβe deformability is a bulk property it can be modified - and, specifically, increased (so that a greater deformation is caused by a smaller applied force⁾ - by simply reducing the bulk of the material in the relevant region (while, of course, keeping the between-wire dimension in the deformation direction constant). Thus, for example, the wire-containing reinforcing layer may (conveniently when it is produced as a separate item subsequently to be bonded to inner inflation and/or outer sealing layers) be provided with narrow slots, or cuts, therein extending normally (that is, perpendicularly) from the surface on one ⁽or both⁾ sides down into the material between the reinforcing wires in such a way that the effective bulk of the material resisting deformation is very much reduced - a thinned version of itself. As a result, the layer as a whole will deform - stretch - by a process rather like that of a concertina opening, involving twisting and bending of the material as well as true elastic stretching. Both this ability to twist and bend and the reduced bulk of the effective sleeve material provides additional deformability, and by appropriately adjusting the slot size and depth so it can be arranged that the deformability in the wire region matches that of the bulk sleeve material.

An alternative method of reducing the effective bulk of the material in the wire region is to provide the wire layer not with slots but with tubular holes extending between and parallel with the wires themselves (this is, in a sense, rather like making the reinforcing layer of a foamed material, albeit with much larger, and more regular "cells" than conventionally found in a foam). Clearly, by adjusting the size (diameter), position, spacing and number of these holes, so the deformability of the wire region can be adjusted to whatever value is necessary to match that of the bulk sleeve material.

Yet another way of achieving matched deformability is to change or choose the very nature of the wires themselves so that taken as a whole the wire-filled region has the desired deformability. Now, it might be thought that the nature of the wire reinforcing elements is essentially fixed, being - as noted hereinbefore - either metal wires or threads or cords of some appropriate plastics substance. However, it is possible to give the element a physical structure other than that of a simple solid "wire-like" object. Specifically, it is possible to form the element as a tube (either hollow or with some very elastic core material) that is itself highly deformable, so that the combination of this tubular element within the material of the reinforced region provides that region with an overall deformability matching that of the surrounding bulk sleeve material. The "wire" reinforcing element may thus itself be in the form of an independently-existing tubular body positioned in, and surrounded by, the material of the sleeve's reinforced region. As an alternative, however, the reinforcing element may take the form of a tube but yet not have an independent existence as such, being instead merely a collection of sub-elements, each conveniently in the form of a thread of a suitable substance, uniformly positioned within and lining a tubular hole through the reinforced region. The hole is then rather like one of the parallel holes mentioned hereinbefore for modifying the structure of the region's material.

The purpose of ensuring that the deformability of the region containing the wire reinforcing elements is matched to that of the bulk material making up the rest of the sleeve is so that, when the sleeve is elastiσally deformed, the tendency for the reinforcing elements to de-bond is reduced or even eliminated, and as a result the deformation is more uniform throughout the relevant part of the sleeve. The way in which this matching has the desired wire-de-bonding effect, and so results in the even disposition of the wires being maintained, and in the consequent uniform inflatory deformation of the sleeve, is explained hereinbefore, and needs no further comment here. Various embodiments of the invention are now described, though by way of illustration only, with reference to the accompanying diagramma t i c Drawings in which:

Figure 1 shows a vertical section through a packer of the inflatable sleeve type in place on a tubing string down the borehole of an oil well;

Figure 2 shows a perspective view (from above) of part of the reinforcing layer within the packer of Figure 1, depicting (in a grossly exaggerated manner) the layout of the meridianal reinforcing elements therein; and

Figures 3A to D show, by way of sections through the sleeve material in both unstretched and stretched form, representations of several different ways of achieving the desired matching deformability.

The inflatable sleeve packer shown in Figure 1 comprises in essence a tubular sleeve (11) sealingly mounted at each end into one of two "shoes" (12t., 12b) slidably mounted on the hollow mandrel (13) of a tubing string. The mandrel is shown positioned down the borehole (generally 14) of an oil well, the hole being lined with a layer (15) of concrete. The sleeve 11 is made of an elastically deformable material having running up and down therealong, internally thereof, a multiplicity of wire-like reinforcing elements. These are not shown in Figure 1, but can be seen in Figure 2, which depicts, in grossly exaggerated form, the general layout of the top portion (corresponding to the portion referenced generally 16 in Figure 1) of the reinforcing elements (as 21) - closely spaced, and running in parallel along meridians of the sleeve.

In Figure 1 the sleeve 11 is shown inflated by fluid pumped thereinto via a (valved) aperture (17) from within the mandrel 13. When inflated the sleeve's outer surface bears sealingly against the inner surface of the borehole's lining 15, so as to separate the borehole section above the packer from that below (except by way of any through passageway - not shown here - in the mandrel itself). When deflated, the sleeve contracts to fit more or less tightly around the mandrel 13, and it can either be moved up the mandrel (and up the rest of the tubing string) and then removed from the borehole entirely or it can be moved up or down along the mandrel to wherever it is next required.

Figures 3A to D show sections through a number of different sleeve materials of the invention, illustrating the several ways in which matching deformability can be attained.

In Figure 3A there is shown a sleeve in which the wire-containing region (31) is a layer of a foamed material in which the individual wires (as 32) are uniformly retained (mostly in a relative positional manner rather than in any absolute way) . As the sleeve as a whole stretches (Figure 3B) , so the wire-containing foam layer easily stretches likewise to match the deformation in the inner and outer layers (33i_, 33o , thus avoiding setting up any de-bonding shear forces across the (notional) boundaries around the individual wires. Accordingly, the relative positioning of the wires 32 remains the same - uniform - and there is little if any chance of the sleeve inner layer 33i being extruded through the wires, and then rupturing.

Figures 3B and 3C show two different ways of attaining matching deformability by changing the structure of the sleeve material in the wire region. In the sleeve of Figure 3B an oblong-section slot (as 41) has been formed extending all along the sleeve between each pair of adjacent wires 32, while in the sleeve of Figure 3B a tubular hole (as 42) has been similarly formed. In each case the effect is much the same; the infinite elasticity of the empty space defined by the slot or hole, coupled with the much easier deformation of the remaining sleeve material between the wires, means that the deformability of the wire-containing region as a whole is much increased, to the point at which it matches that of the surrounding bulk sleeve material, and so when the sleeve stretches there are again avoided the sort of shear-inducing forces that would otherwise tear the wires loose and cause non-uniform expansion (and wire separation). Accordingly, sleeve extrusion and rupture is prevented.

The embodiment of Figure 3D is one wherein the reinforcement takes the form of a multiplicity of meridianal tubular holes (as 44) lined with thread-like reinforcing elements (as 45). The effect of these holes 44 is much the same as that of the similar holes 42 in the Figure 3C embodiment, and it will be clear how, in operation, the holed region can easily deform to match the deformation of the surrounding sleeve material without any significant danger that the reinforcing elements 45 lining the holes will tear loose, causing non-uniform inflation, sleeve extrusion, and consequent sleeve rupture and failure.

Claims

1. A packer of the wire-reinforced inflatable sleeve type, wherein the deformability of the region containing the wire reinforcing elements is matched to that of the bulk material making up the rest of the sleeve, so that, when the sleeve is elastically deformed, the tendency for the reinforcing elements to de-bond is reduced or even eliminated, and as a result the deformation is more uniform throughout the relevant part of the sleeve, and the reinforcing elements retain their equal spacing thereby minimizing the largest gap of unsupported sleeve material .

2. A packer as claimed in Claim 1, wherein the sleeve has only one layer of reinforcement.

3. A packer as claimed in either of the preceding Claims, wherein the reinforcing elements are disposed parallely side by side slightly spaced one from the other.

4. A packer as claimed in any of the preceding Claims, wherein matching deformability is achieved by the nature of material in the wire region having an appropriately different elasticity from that of the bulk, wire-free material, and this is attained by making the wire- containing layer from a less-vulcanised version of the material used for the bulk of the sleeve, or by using a foamed version of that bulk material, or by employing a completely different elastomeric material for the wire- containing layer.

5. A packer as claimed in any of Claims 1 to 3, wherein matching deformability is achieved by the actual physical structure of the elastic sleeve material in the wire region having the required matching deformability, and this is attained by providing the wire-containing reinforcing layer either with narrow slots, or cuts, therein extending normally (that is, perpendicularly) from the surface on one (or both) sides down into the material between the reinforcing wires, or with tubular holes extending between and parallel with the wires themselves.

6. A packer as claimed in any of Claims 1 to 3, wherein matching deformability is achieved by the very nature of the wires themselves, and this is attained by the use of wire reinforcing elements each of which is formed as a tube that is itself highly defor able.

7. A packer as claimed in any of the preceding Claims and substantially as described hereinbefore.