WO1991019882A1

WO1991019882A1 - Tools for wells

Info

Publication number: WO1991019882A1
Application number: PCT/GB1991/000938
Authority: WO
Inventors: Paul Douglas Maxfield Gullett
Original assignee: Stirling Design International Limited
Priority date: 1990-06-12
Filing date: 1991-06-12
Publication date: 1991-12-26
Also published as: GB9013110D0

Abstract

A tool for an oil well comprises a casing section (10) which carries a device (16; 25; 41) which is capable of moving to a position to block the gap between the casing section (10) and an associated hole. The tool is provided with passages (18; 37; 49; 50) which allow drilling mud or other fluid to be displaced from the annular space behind the tool by another fluid such as a cement slurry. The passages may contain an additive which reacts to an additive in the cement slurry to block the passages once the cement starts to pass through the passages. In this way, complete filling of the annular space is achieved without excess cement passing to other regions. Such a tool can be used in the selective treatments of sections of an oil well hole, particularly for a horizontal application, and can be used to isolate a gas zone in a vertical hole.

Description

TOOLS FOR WELLS

The invention relates to tools for wells such as oil or gas wells.

A well such as an oil well is formed by a hole drilled through underground formations into which a casing string is inserted. A cement slurry is pumped between the casing and the hole to hold the casing string in position and, in the portion of the formation which bears the material being sought, the casing is provided with inlets in the form of slots or holes through which the material can pass via the casing to the surface.

*• In some bearing formations, the composition of the formation is uniform so that material is extracted generally uniformly throughout the whole length of the casing within the bearing formation. However, in some bearing formations, material may not be produced uniformly throughout the formation; there may be sections of the formation from which no material is received or from which unwanted materials such as gas or water only may be received.

In order to maximize the production of oil wells, it is increasingly common to drill the well hole not only vertically but also deviated and horizontally, so that it extends laterally into the oil bearing formation. The extent of these lateral runs may be up to 1000 metres or more. Such horizontal wells will encounter more variations in production along their length than will vertical wells. For example, some sections of a horizontal well may cease yielding as a result of some reservoir discontinuity or some sections may pass through water bearing zones. In some horizontal wells, this problem is not addressed at all, the casing string within the horizontal section remains open along its length and receives material and whatever fluids the formations may yield. In other cases,^" the casing string is cemented in position along the whole length of the horizontal well and is then explosively perforated where yield is required or material is extracted only from the open end of the casing string. This has the disadvantage, however, that very large volumes of cement must be pumped, requiring very exacting slurry designs. It is also a problem with .this technique that it is difficult to ensure that the space between the casing and the hole is completely filled. A very narrow passage may be left at the top of the hole through which gas or other fluids can migrate to the surface or to another zone, with consequent undesirable problems.

Another technique has been the use of external casing packers in the form of long tubes of flexible material which are mounted on the exterior surface of the casing string and which are distended to block the gap between the casing string and the associated hole. Such packers are, however, very expensive, and do not provide long term isolation from experience to date.

According to the a first aspect of invention, there is provided a tool for a well comprising a casing section having an outer surface on which is mounted a containment device operable to move from a retracted position adjacent to the outer surface to an operative position in which, in use, the device blocks the annular space between the casing section and a surrounding formation, the device including at least one passage extending between axially spaced ends of the device, the at least one passage being selectively closable to prevent _.the passage therethrough of a predetermined fluid.

Thus, by the use of two such tools at spaced intervals along the casing, a section of a formation can be isolated and an appropriate material pumped into the annular space between the two tools. As the material, or a substance in the material, reaches the passages, they close so ensuring that the annular space is completely filled and yet excess of the material is not required. The material may, for example, be cement slurry for permanent hydraulic isolation or a gravel pack or resin slurry for consolidation purposes.

According to a second aspect of the invention, there is provided a tool for an oil well comprising a casing section having an outer surface on which is mounted a containment device operable to move from a retracted position adjacent said outer surface to an operative position in which, in use, the containment device divides the space between the casing section and an adjacent formation into at least one passage extending around the casing section, the casing section having an interior surface provided with an inlet leading to said at least one passage for the supply to said passage of a settable material to block said space.

According to a third aspect of the invention, there is provided a method of isolating the section of a well hole comprising inserting into a casing string at two spaced intervals therealong a tool according to the first aspect of the invention, inserting the casing string into the well hole until the tools are at the section of the surrounding formation to be isolated, moving the device from the retracted position to the operative position, and then pumping a predetermined flowable material into the annular space defined between the exterior surface of the casing and the surrounding formation and between the tools, the at least one passage being arranged so that closure is completed when the annular space is wholly filled with said flowable material.

According to a fourth aspect of the invention, there is provided a method of isolating a gas zone in a vertical hole well comprising inserting into the hole a casing string including a slotted liner, a packer above the slotted liner and a tool according to the first aspect of the invention above the packer, locating the slotted liner in the gas formation^ with the packer above the gas formation, operating the packer to close the annular space between the exterior surface of the casing and the surrounding formation and moving the device of the tool from the retracted position to the operative position, inserting into the casing a tube having at the end thereof a tool to which a cement slurry is supplied to the annular space defined between the packer and the tool and the exterior surface of the casing and the surrounding formation to fill said annular space with cement.

The following is a more detailed description of some embodiments of the invention, by way of example, reference being made to the accompanying drawings in which:-

Figure 1 is a longitudinal cross-section of a first form of tool ^"for an oil well, the first tool being in a retracted position,

Figure 2 is a cross-section through the retracted tool of Figure 1 in a plane normal to the plane of the section of Figure 1, Figure 3 is a similar view to Figure 1 but showing the tool in an operative position,

Figure 4 is a cross-section of the first tool similar to that of Figure 2 but showing the first tool in an^' operative position.

Figure 5 is a schematic cross-section through a passage of the first tool of Figures 1 to 4,

Figure 6A is an axial cross-section of the first tool of

Figures 1 to 5 mounted in a casing in a horizontal oil well with the first tool in a retracted position,

Figure 6B is a section on the line VI-VI of Figure 6A,

Figure 7A is a similar view to Figure 6A but with the first tool in the operative position with an annular space between the casing and the surrounding hole partially filled with cement slurry,

Figure 7B is a section on the line VII-VII of Figure 7A,

Figures 8A is a similar view to Figure 6A and Figure 7A but showing he annular space almost completely filled with cement slurry,

Figure 8B is a section on the line VIII-VIII of Figure 8A

Figure 9 is an axial cross-sectional view of a second form of tool combined with a centralizer, with both the tool and the centralizer in a retracted position,

Figure 10 is a section on the line X-X of Figure 9, with the tool and centralizer both in the retracted position.

Figure 11 is a similar view to Figure 9 but showing arms of the centralizer released to an operative position and the tool in the retracted position.

Figure 12 is a section on the line XII-XII of Figure 11,

Figure 13 is a similar view to Figures 9 and 11 but showing the tool and the centralizer in operative positions.

Figure 14 is a section on the line XIV-XIV ofFigure 13,

Figure 15 is a longitudinal cross-section of a first form of tool combined with a centralizer of the kind shown in Figures 10 to 14, both the centralizer and the tool being in retracted positions,

Figure 16 is a radial cross-section on the line XVI-XVI of

Figure 15,

Figure 17 is a similar view to Figure 15 but showing the centralizer in an operative position but the tool in a retracted position.

Figure 18 is a_. section on the line XVIII-XVIII of Figure

17,

•Figure 19 is a similar view to Figures 15 and 17 but showing both the centralizer and the tool in operative positions, one form of plate of the tool being shown at the top of the Figure and a second form of the plate of the tool being shown at the lower half of the Figure,

Figure 20 is a section on the line XX-XX of Figure 19,

Figure 21 is a view of detail A marked in Figure 19,

Figure 22 is a view of detail B marked in Figure 19,

Figure 23 is a schematic cross-sectional view of a fourth form of tool in a retracted position, showing a tool positioned in an associated casing to supply a fluid to the tool,

Figure 24 is a similar view to Figure 23 but showing the fourth form of tool in an operative position,

Figure 25 shows two tools of any of the kinds described above with reference to Figures 1 to 22 mounted at spaced intervals along the casing in a horizontal oil well with a cemented section between them,

Figure 26 ^• shows two tools of any of the kinds described above with reference to Figures 1 to 22 mounted on a casing of a vertical oil well above a standard external casing packer in order to isolate a gas zone with a cement cap, the tool being used in a first stage of the process and.

Figure 27 is a similar view to Figure 25 but showing a second stage in the process. Referring first to Figures 1 to 5, the first tool comprises a casing section 10 having an interior surface 11 and an exterior surface 12. The interior surface 11 is provided with an internal threaded connection 13 at one end to allow the casing section 10 to be connected in an oil well casing string. At the opposite end of the casing section 10, the exterior surface 12 is provided with an external threaded connection 14 for a similar purpose.

The exterior surface 12 of the casing section 10 is also formed with two axially spaced annular ribs 15 projecting above the exterior surface 12. A sleeve 16 of a flexible material such as natural or artificial rubber is located between the ribs 15. One end of the sleeve 16 is in sealing engagement with*- the rib 15 and the other end of the sleeve 16 is mounted on a ring 17 capable of sliding axially along the exterior surface 12 of the casing section 10.

A number of tubes 18 are moulded into the material of the sleeve 16 intermediate its ends. As seen in Figure 2, there are 16 such tubes 18 spaced equi-angularly around the sleeve, but there may be more or less tubes as desired.

The dimensions of the tubes 18, the sleeves 16 and the ribs 15 are such that, in the retracted position of the tool as shown in Figures 1 and 2, the tubes 18 and the sleeve 16 do not project radially outwardly of the radially outer ends of the ribs 15. This feature provides^"some protection for the sleeves 16 and the tubes 18 when the tool is being deployed in an oil well.

An aperture (not shown) is provided connecting the space between the exterior surface 12 and the sleeve 16 to the interior of the casing section 10. In a first form of the device this may be the only such connection. In a second form, however, a branch (not shown) leads from this aperture to the exterior surface of the casing portion 10 and includes a shuttle valve (not shown) which allows the passage of fluid from the aperture through the branch only when a predetermined pressure is exceeded. The function of this branch will be described in more detail below.

The operation of the tool will be described briefly with reference to Figures 3, 4 and 5 and its use will be described in. more detail below. In operation, fluid is pumped through the aperture into the space between the external surface 12 and the sleeve 16 to distend the sleeve 16 with the ring 17 sliding on the exterior surface 12. In this position, the tubes 18 are spaced outwardly of the casing section 10, as best seen in Figure 4. Each tube, as seen in Figure 5, has an inner wall 19 coated with an additive X. This additive X is designed to react with another additive Y in a fluid passing through the tube 18 to cause a rapid set, closing each tube 18 in turn. For example, X may be sodium silicate and Y calcium carbonate. The function of this in use will be described in more detail below.

Referring now to Figures 6A, 6B, 7A, 7B, 8A and 8B, in use the casing section 10. is inserted in a casing string 20 which, in this case, is passed into a hole 21 of a horizontal oil well. One of the casing string may be a slotted liner 22. As seen in Figures 6A and 6B, the tool is in the retracted position with the ribs 15 bearing on the hole to provide some protection for the sleeve 16 and the tubes 18. Next, referring to Figures 7A and 7B, a tool 23 is inserted into the casing string and a cement slurry passes from the well head through a tube 24 to the tool 23 and from the tool 23 into the space between the exterior surface 12 and the sleeve 16 via the aperture. This distends the sleeve 16 as described above with reference to Figures 3 and 4 until the sleeve contacts the hole 21. A tool 23 for this purpose is the subject of our U.K. Patent Application No. 9013111.

As seen in Figure 7A, in this position the tubes 18 are arranged parallel to the axis of the casing string 20 but adjacent the surface of the hole 21. In addition, in this position, the sleeve blocks the space between the casing string 20 and the hole 21, apart from the passages provided by the tubes 18.

The tool 23, in the second form, also provides cement slurry to the annular space behind the tool, via the branch described above which opens as the pressure rises once the sleeve 16 has been filed. This space has previously been filled with drilling mud or water. As the cement slurry fills this space, the drilling mud is displaced through the tubes 18 until it has been dispelled, when the cement slurry begins to pass through the tubes 18. As it does so, additive Y (for example calcium carbonate) provided in the cement slurry reacts to additive X (for example sodium silicate) inside each tube 18 to close the tubes 18.

It will be appreciated that not all the tubes 18 will close simultaneously since, in a horizontal hole 21, the annular space will fill from the bottom upwards, so that the tubes 18 will gradually close. This is best seen in

Figures 7A, 7B, 8A and 8B, where Figures 7A and 7B show the annular space just beginning to fill with only six of the tubes 18 being closed, whereas Figures 8A and 8B show the annular space nearly wholly filled with only three tubes 18 remaining unfilled. In this way, complete cementing of the annular space is ensured without the possibility of any passages being formed at the top or any part of the hole 21.

Referring now to Figures 9 to 14, the second tool 25 is combined with a centralizer 26. The second tool 25 comprises a casing section 27 having an exterior surface

28 on which is provided a pair of axially spaced annular ribs 29. A sleeve 30 of a flexible material such as natural or artificial rubber is arranged between the ribs

29 with one end of the_*sleeve 30 being fixed to one of the ribs 29 and the other end of the sleeve 30 being carried on a ring 31 which is capable of axial sliding movement over the exterior surface 28. An aperture (not shown) connects the space between the exterior surface 28 and the sleeve 30 to the interior of the casing section 27. In a first form of the device, t is may be the only such connection, but in a second form of the device, the aperture also connects to the exterior surface of the casing.

The centralizer 26 comprises six generally U-shaped springs 32 arranged equi-angularly around the exterior surface 28 of the centralizer 26 axially adjacent the second tool 25. Each spring lies in a respective plane including the axis of the casing section 27. Each spring 32 has one limb 33 fixed to a rib 29 and the other limb 34 mounted on a ring 35 able to slide axially along the exterior surface 28 of the casing section 27. A strap 36 holds the springs 32 in the retracted position shown in Figures 9 and 10 until released as described below.. A plurality of tubes 37 pass through the casing section 27 in a direction parallel to the axis of the casing section 27 and beneath the ribs 29 and the sleeve 30. As seen in Figure 10, twelve such tubes are provided.

One end 38 of each tube opens on the surface of a rib 29 remote from the centralizer 26. The other end 39 continues as a flexible tube 40 connected to an adjacent limb 33 of a spring 32. Thus in the retracted position shown in Figures 9 and 10, the tubes 40 lie adjacent the exterior surface 28 of the casing section 27 with the ribs 29 projecting outwardly of and protecting the sleeve 30, the springs 32 and the flexible tubes 40 to protect them as they pass through the well hole.

The second tool 25 and the centralizer 26 are deployed in the following way. First, material is pumped into the space between the exterior surface 28 and the sleeve 30 to distend the sleeve to the position shown in Figure 13 in which the outer surface of the sleeve 30 contacts the surface of the hole. Simultaneously, slurry under pressure is supplied to a release device (not shown) associated with the strap 26 to operate the device and release the strap 26. This releases the springs 32 which then move to the operative position shown in Figures 11 and 12 with the ring 35 sliding along the exterior surface 28. In this position, the springs 32 engage the hole to locate the casing section 27 centrally in the hole. At the same time, the ends of the flexible tubes 40 are raised so that they are adjacent the surface of the hole. slurry Since the springs 32 of the centralizer 36 take the weight of the casing section 27, the sleeve 30 can be of lower rating and cost than the sleeve 16 of the embodiment described above with reference to Figures 1 to 8B. When the sleeve is fully distended in the second form of the tool, a valve opens and allows a cement slurry to be pumped into the annular space behind the distended sleeve 30 as described above with reference to Figures 6A to 8B. Drilling mud or any other fluid in the annular space displaced by the cement slurry passes through the flexible tubes 40, through the tubes 37 to exit through the tube ends 38. As described above with reference to Figure 5, the tubes 37 contain an additive X (such as sodium silicate) which reacts with an additive Y (such as calcium carbonate) provided in the cement slurry to close the •tubes 37. In this way, the drilling fluid in the annular space is reliably dispelled. The positions of the ends of the flexible tubes 40 adjacent the surface of the hole ensures that the annular space behind the distended sleeve 16 is completely filled with cement slurry leaving no passages.

Referring next to Figures 15 to 20, a third form of tool 41 is also combined with a centralizer 42. This is the same as the centralizer described above with reference to Figures 9 to 14 and so it will not be described in detail and its parts will be given the same reference numerals as the corresponding parts in the centralizer 26.

The third tool 41 comprises a casing section 43 provided with an exterior surface 44 formed with two annular axially spaced ribs 45. Six curved plates 46 are arranged between the ribs 45 and are each hinged at one end for pivotal movement about axes normal to the axes of the casing section 43. Springs (not shown) act on the plates 46 to tend to pivot the plates about the hinges 47 outwardly of the exterior surface 44 of the casing section 43. The ends of the plates 46 opposite the hinges 47 are held against such movement in a retracted position by a strap 48 (see Figures 15 and 17) whose ends are held together by a release mechanism (not shown) . The ribs 45 have their ends arranged radially outwardly of the plates 46 to protect the plates 46 as they pass through the well hole.

In use, the third tool 41 and the associated centralizer 42 are deployed in a horizontal hole- as described above with reference to Figure 6A. The centralizer springs 32 are then moved to an operative position as described above with reference to Figures 9 to 12 to locate the casing string centrally in the hole. Next, the pressure of the slurry is applied to the release mechanism for the strap 48 via a branch passage (not shown) to release the plates 46 which pivot about the* hinges 47 under the action of the springs (not shown) to the operative position shown in Figure 19. The plates 46 are so shaped that, in this operative position, their ends engage the associated hole (not shown) and they engage each other cirumferentially to form a complete annulus of plates extending between the exterior surface 44 and the hole.

Alternative constructions of the plates 46 are shown in the upper and lower halves of Figures 19 and 20 respectively. The plates 46A in the upper half of Figure 19 are provided with a plurality of holes 49 which extend through the plate 46. This is shown in more detail in Figure 21. Each hole 49 is coated with additive X which reacts with additive Y in a cement slurry to close the holes 49 in a manner described above.

The plates 46B in the lower half of Figure 19 are formed of a very fine mesh 50, best seen in Figure 22. This is designed so that, when water is initially between the casing string and the hole, such water can be dispersed through the mesh by the cement slurry. However, the mesh prevents the cement slurry passing because of its denser particulate composition which plugs the mesh.

The third tool 41 also has two forms. In a first form, a connecting aperture is provided only between the release mechanism and the interior of the casing section 43 to operate that mechanism. In a second form, the aperture also leads to the exterior surface of the casing section 43 via a shuttle valve.

Referring next to Figures 23 and 24, the fourth form of tool comprises a casing 70 provided with an exterior surface 71 formed with an annular recess 72. A mesh screen 73 is within the recess 72, spaced from the surface of the recess 72 to form a chamber 74 containing a substance whose properties will be described below.

Above the mesh screen 73 are a plurality of plates 75 pivotally connected to the casing 70 for movement between the retracted position shown in Figure 23 and the operative position shown in Figure 24. When in the operative position shown in Figure 24, the plates 75 form a spiral passage extending from one end of the tool to the other. When in the retracted position, the plates 75 do not project radially outwardly of the casing outer surface 71 and are thus protected by the casing 70. Two inlets 76 are provided at diametrically, opposed sides of the interior surface of the casing 70 and lead to the chamber 74, via respective check valves 77, which allow flow only from the inlets 76 to the chamber 74.

In use, the casing 70 is inserted in a casing string, as described above with reference to Figure 6A. The tool is then located at a required position in an oil well hole. A tool 78, preferably of the kind described in our UK Patent Application No. 9013111, is then located at the inlets 76 to provide a passage to the inlets 76 from coil tubing 79 connected to the tool 78.

A cement slurry is then passed to the inlets 76 from the tool 78 and so passes into the chamber 74. The substance in the chamber 74 is a substance which, when mixed with a cement slurry, causes the slurry to harden rapidly. For example, the cement slurry may contain calcium chloride and the chamber 74 may contain calcium silicate. The mixture of slurry and substance then emerges through the mesh screen 73. This causes the plates 75 to move from the retracted position shown in Figure 23 to the operative position shown in Figure 24 where the plates 75 form the spiral passage and block the gap between the casing and a surrounding formation.. Alternatively, a two part resin system may be used, with the hardener being in the chamber

74 and the resin supplied through the tool 78.

The mixture fills the passage and solidifies, so blocking the passage and the annular gap between the casing (70) and an adjacent formation. The spiral configuration of the passage ensures that the mixture extends all round the casing, resisting any tendency of the mixture to congregate to one side of the casing 10.

Of course, there need not be a single passage, the plates

75 could divide the annular space between the casing section 70 and an adjacent formation into at least one passage extending around the casing section 70.

Referring next to Figures 23 to 26, these Figures show some possible uses of the tools described above with reference to the drawings. Describing these drawings, reference will be made to a "tool 55" and this is to be interpreted as being a tool of any of the kinds described above with reference to the drawings.

Referring first to Figure 25, this application shows a horizontal well formed by a hole 56. A casing 57 extends through the hole 56.

It may be found prior to setting the casing that one portion of the surrounding formation 58 does produce oil, or produces oil at such a low rate as to make recovery not worthwhile. In this case, two tools 55 are provided spanning this section the uphole tool 55 being of the first form and the downhole tool 55 of the second form. The two tools 55 are,^moved to operative positions as described above with reference to the drawings to isolate this section, the uphole tool 55 being operated before the downhole tool. A cement slurry can then be pumped into the annular space between the tools 55 after the downhole tool 55 has been operated to provide a cemented section 59 between the tools 55, so . isolating the section. Subsequently, if the section is required to be worked again, the cemented section 59 may be perforated by explosives in a known manner to form perforations 60 for the passage of oil.

Referring next to Figures 26 and 27, there is shown the application of the tool 55 in a vertical well. It is a problem in such vertical wells to cement the casing 63 in place when gas migration is possible from the formation 64. It -is normal practice to cement the whole casing 63 including the portion of the casing 63 passing through the gas formation. It is a problem, however, that when the cement sets, it passes through a period when its specific gravity decreases so that it exerts much less force than it does when in slurry form. In fact, there may be a period when it exerts only the same force as a corresponding volume of water. During this period, the pressure of the gas may be such that it can pass throug the setting cement destroying zonal isolation and causing communication even as far as the surface and this is plainly undesirable. In the arrangement described with reference to Figures 26 and 27, this is avoided in the following way.

First, the casing 63 is provided with a slotted liner 66 across the gas formation. The slotted liner 66 is beneficial because, unlike perforated liners, it provides a known flow restriction to the well bore. In addition, the slotted liner can also be a "screen liner" when placing a gravel pack behind it.

Next, a standard external casing packer 67 is placed around the casing 63 just above the gas formation 64. This is a flexible sleeve which is distendable to close the annular space between the exterior of the casing 63 and the hole 65.

Next, a tool 55 in its first form is provided on the casing 63 above the packer 67 and is moved to an operative position as described above with reference to the drawings. A tube tool 68 is then moved adjacent the containment tool 55 and a cement slurry is supplied to operate the tool 55 as described above with reference to the drawings. A suitable tube tool 68 is the subject of our co-pending U.K. Patent Application No. 9013111. The tube tool is then moved to a position adjacent the casing packer 67 and cement slurry is then pumped into the sleeve of the packer 67 to distend it so that it closes the annular space between the exterior of the casing 63 and the hole 65. When this is complete a valve opens to connect the tube tool 68 with the annular space between the tool 55 and the packer 67 where it displaces the water or drilling mud and sets.

The annular space between the tube 70 and the interior space of the casing 63 is filled with drilling mud and a bypass (not shown) is provided through the tool 68 so that the pressure of the drilling mud above the tool 68 is applied to the drilling mud portion of the casing 63 below the tool 68.

By this method, the gas in the gas formation 64 is isolated in two ways. First, it is prevented from passing through the cement in the annular space 69 by the packer 67 and so there is no possibility of the gas passing through the cement as its applied force is reduced during setting. Secondly, the bypass in the tool 68 ensures that the drilling mud pressure is applied to the gas formation throughout the cementing operation so again holding the gas in the formation.

After this cementing step, the tool 68 is raised in the casing 63 to a position above the tool 55 and cement slurry is passed into the remainder of the annular gap between the casing 63 and the hole 65 above the tool 55 to complete the cementing operating. Again, the bypass through the tool 68 maintains the hydrostatic pressure of the drilling mud on the gas formation 64 during cementing. The presence of the cemented annular section 69 beneath the tool 68 prevents any gas passing through the setting cement in the second stage.

It will be appreciated that the tools described above with reference to the drawings may be used for applications other than those described above. For example they may be used in gas or other wells. In addition, the tools themselves may be modified in a number of ways. For example, the tubes need not be closed by the use of reacting chemicals, they could be closed mechanically or electrically. The sleeves or the leaves need not be mounted directly on a casing section, they could be carried by a member which is then mounted on the casing section.

Claims

1. A tool for a well comprising a casing section (10) having an outer surface on which is mounted a containment device (16;25;41) operable to move from a retracted position adjacent to the outer surface to an operative position in which, in use, the device blocks the annular space between the casing section and a surrounding formation (61;65), the device including at least one passage (18;37;49;50) extending between axially spaced ends of the device, the at least one passage (18;37;49;50) being selectively closable to prevent the passage therethrough of a predetermined fluid.

2. A tool according to claim 1 wherein the device includes a sleeve (16;30) of an elastomeric material which surrounds the associated casing section (10) and which has the ends thereof in sealing engagement with the outer surface of the casing section, said sleeve being distendable to- said operative position.

3. A tool according to claim 2 wherein one end of the sleeve (16;30) is mounted on a ring (17;31) free for sliding movement on said outer surface as said sleeve (16;30) is distended so that opposite ends of the sleeve (16;31) approach each other as the sleeve distends.

4. A tool according to claim 2 or claim 3 wherein the at least one passage is provided by a tube (18) carried by the sleeve (16) of elastomeric material and extending in a direction parallel to the length of the casing section (10) such that, in the operative position, the at least one tube (18) is at the periphery of the distended sleeve (16).

5. A tool according to claim 4 wherein a plurality of said tubes (18) are provided spaced around the sleeve (16).

6. A tool according to claim 4 or claim 5 wherein, in the retracted position of the sleeve (16), the at least one tube (18) is disposed between, and radially inwardly of, a pair of axially spaced annular ribs (15) provided on the outer surface of the casing section (10) to protect the

^■ sleeve (16) during location of the tool in the formation.

7. A tool according to claim 1 wherein the containment device comprises a plurality of plates (46) arranged

. around said outer surface of said casing section (10) and hinged for pivotal movement between said retracted and said operative positions.

8. A tool according to claim 7 wherein spring means are provided which urge said plates (46) towards said operative position and wherein a strap (48) is provided which normally holds said plates (46) in a retracted position but which is capable of being rendered inoperative to release the plates (46) for movement under the action of said spring means to said operative position.

9. A tool according to claim 7 or claim 8 wherein each plate is provided with a plurality of holes (49) extending therethrough and forming said at least one passage, each hole (49) containing a substance which reacts with said predetermined fluid to block the associated hole (49) and thereby provide said selective closing.

10. A tool according to claim 7 or claim 8 wherein each plate (46) is formed from a mesh (50) that permits the passage of water therethrough but prevents the passage of a slurry.

11. A tool according to claim 8 wherein the plates are arranged in said operative position, to form a spiral passage extending around the casing section (10), the casing section (10) including a chamber having an inlet leading to the exterior of the casing section (10) and an outlet leading to the exterior surface of the casing section at the plates, the chamber containing a substance which so reacts with said predetermined fluid that when said predetermined substance is supplied to the inlet, the predetermined substance mixes with said reacting substance and emerges from said outlet to fill said spiral passage to block said passage.

12. A tool according to claim 8 or claim 9 wherein the at least one passage is provided by a tube (37) extending through said casing section (10) in a direction parallel to the axis of the casing section (10) and radially inwardly of the associated sleeve.

13. A tool according to claim 12 wherein one end of the at least one tube (37) passing beneath the sleeve is connected to a flexible tube (40) which is movable from a retracted position adjacent the outer surface of the casing section to an operative position in which an open end of the flexible tube (40) is spaced from said outer surface and is, in use, adjacent a surrounding formation.

14. A tool according to claim 13 wherein the casing section also carries a plurality of generally U-shaped springs (32) spaced around the outer surface of the casing section a'nd lying in respective planes including the axis of the casing section (10), each spring (32) being held in a retracted position but being releasable to move to an operative position in which the springs (32) adopt said U-shape for, in use, centralizing the casing section (10) in an associated surrounding formation.

15. A tool according to claim 14 wherein each flexible tube (40) is attached to an associated U-shaped spring (32) so that, in the retracted position of each U-shaped spring (32), the associated flexible tube (40) is^' maintained in said retracted position adjacent the outer surface of the casing section (10), and in the operative position of each U-shaped spring( 32), the flexible tube (40) is moved to said operative position.

16. A tool according to any one of claims 1 to 6 or 8 to 10 or 12 to 15 wherein the at least one passage (18;37;49) contains a substance which reacts with said predetermined fluid to block the associated passage (18;37;49) and thereby provide said selective closing.

17. A tool for an oil well comprising a casing section (70) having an outer surface (71) on which is mounted a containment device (75) operable to move from a retracted position adjacent said outer surface to an operative position in which, in use, the containment device (75) divides the space between the casing section (70) and an adjacent formation into at least one passage extending around the casing section (70), the casing section (70) having an interior surface provided with an inlet (76) leading to said at least one passage for the supply to said passage of a settable material to block said space.

18. A tool according to claim 17 wherein the inlet (76) leads to a chamber (74) provided in the casing section (70), the chamber (74) containing a substance which combines with a material supplied through said inlet (76) to provide said settable material.

19. A tool according to claim 17 or claim 18 wherein the containment device comprises a plurality of plates (75) pivotally connected to the casing section (70) and, in ^• said operative position, forming a spiral passage extending along the outer surface (71) of the casing section, to provide said at least one passage.

20. A tool according to claim 20 wherein the plates (75) are moved to said operative position by the supply of said settable material to the spiral passage.

.

21. A tool according to any one of claims 17 to 20 wherein the inlet (76) includes a valve (77) permitting flow only from the interior to the exterior of the casing section (70) .

22. A method of isolating a section of a well hole comprising inserting into a casing string (57) at two spaced intervals therealong a tool according to any one of claims 1 to 16 (55), inserting the casing string into the well hole until the tools are at the section of the surrounding formation to be isolated, moving the devices of the tools (55) from the retracted position to the operative position, and then pumping a predetermined flowable material into the annular space defined between the exterior surface of the casing and the associated surrounding formation (61) and between the tools (55), the at least one passage being arranged so that closure is completed when the annular space is wholly filled with said flowable material.

23. A method of isolating a gas zone in a vertical hole well comprising inserting into the hole a casing string including a slotted liner (66), a packer above the slotted liner and a tool according to any one of claims 1 to 16 above the packer, locating the slotted liner in the gas formation, with the packer (67) above the gas formation, operating the packer (67) to close the annular space between the exterior surface of the casing and the surrounding formation and moving the device of the tool (55) from the retracted position to the operative position, inserting into the casing a tube having at the end thereof a tool (68) to which a cement slurry is supplied to the annular space (69) defined between the packer and the tool and the exterior surface of the casing and the hole to fill said annular space with cement.

24. A method according to claim 23 and further comprising providing a by-pass in the cement supplying tool to allow drilling mud pressure to be applied to the gas formation via the slotted liner.

25. A method according to claim 23 or claim 24 wherein the cement supplying tool is moved to a position above the tool, and then cement is supplied to the remainder of the annular space between the casing and the hole above the tool.