EP0457653B1 - Safety sleeve and device for wells, particularly for a subterranean reservoir of fluid under pressure - Google Patents

Description

The present invention relates to tube systems which are arranged within wells, in particular for the exploitation of underground reserves of pressurized fluid, whether these are natural (oil deposits) or artificial (storage cavities in sufficiently impermeable mass). In particular, it is developing a safety device facilitating the closure of any passage between these tubes and the outside of the well. This device is rather called hereinafter "sleeve" because of its very structure. A safety assembly comprising this sleeve, but also a part of the tubes as well as safety valves of known type, also forms part of the invention. It in fact authorizes the implementation of a method of operating the well in which it is disposed, which is particularly advantageous economically and reliable from the safety point of view.

In order to better understand in what technical terms the problem of the safety of wells communicating with underground reserves of fluid arises, we immediately refer to a relatively precise example and illustrate it by the first four figures attached in the appendix. These indeed apply to a particular case of reserve which uses a cavity excavated by leaching in a solid mass of rock salt. According to Figure 1, which gives an idea of the relative dimensions using a graduated vertical axis, this type of cavity can reach volumes of the order of 5x10⁵ m³. A single well 2 connects the cavity 1 to the surface where the operating units 3 are installed. For this, it often crosses salt 6, but also and mainly sedimentary rocks 5 overlying. The leaching technique, which essentially consists of injecting fresh water through a dip tube 10 and recovering this water saturated with dissolved salt - rather called brine - by the ring finger between the tube 10 and a tube called a guard tube not shown and not permanent taking place in the well 2, results in the formation of a cavity 1, but also in the accumulation of insolubles 7 at the bottom of this cavity 1 while it remains filled with brine.

Before being able to store gas, for example, site operators must therefore dispose of this initial brine. This comes in a preliminary phase to the actual operation, called in the profession "dewatering". This is shown diagrammatically in FIG. 2 where two imaginary semi-horizontal cuts have made it possible to maintain relatively realistic relative dimensions. In this way, in fact, the structure of the well 2 emerges better as well as the configuration, specific to this phase, of the tubes which it contains. Starting from the center, we recognize the dip tube 10 which extends practically to the bottom of the cavity 1, its lower end opening just above the insolubles 7. It is also called subsequently central tube. It is surrounded by a casing assembly of the well 2 delimiting an annular 9. This assembly comprises, still going more and more towards the outside of the well: a protective tube 30 (also called hereinafter peripheral tube), a metal casing 20, a cement sheath 25. While the latter extends to the shoe 21 of the well 2 and guarantees good anchoring of the casing to the ground, a liquid of appropriate density, often called in the profession "completion liquid", and based on brine is placed between the protective tube 30 and the casing 20. Retained below by the annular plug 31, this liquid has the function of exerting a support force on the casing 20, the resistance in particular to crushing can thus be reduced.

The "dewatering" then consists in injecting the gas G to be stored by the ring finger 9. Provided that its pressure is sufficient, it pushes back the interface 8 gas / brine towards the bottom of the cavity, brine B being thus forced to go up by the dip tube 10. In this way, the pressurized gas G gradually replaces the brine B within the cavity. When it finally contains only gas, the real phase of storage operation begins. This generally lasts from 20 to 25 years during which gas is drawn up or renewed from time to time. For these operations, the dip tube 10 is most of the time amputated of all or part of its length extending into the cavity. This is why we give it instead the name of central tube 10 by referring to its position in the center of the well. It is by this tube that traditionally, the gas withdrawn is collected at the surface while the ring finger 9 can be voluntarily closed.

This way of operating is explained by the need to provide the well in operation with proper safety devices, in the event of an accident, to interrupt any communication between the cavity 1 under pressure and the surface. However, normally closed type safety valves which are most often used for this purpose adapt more easily to the central tube 10 and cannot be arranged in the annular 9 without additional arrangements. Consequently, operators usually take the precaution of closing this ring finger once the "dewatering" is completed. To this end, various elements have so far been considered. One of them, commonly used at present, is shown in the half-sections of the well 2 in FIGS. 3 and 4. It is an annular mask 40 which is secured within the tube 10 central. This mask 40 has a telescopic part 42 which, depending on whether pressurized oil is supplied by the control line 44 or not, has come out to its maximum length (FIG. 3) or is fully retracted (FIG. 4). In the first case, the mask 40 isolates the interior of the central tube 10 relative to the annular 9. The lateral orifices 11 and 12 formed in the central tube 10 are, on the contrary, placed in communication with each other so that the gas injected during “dewatering” for example can bypass a fixed connection provided between central tube 10 and protective tube 30. In the case of a folded mask, one of the lateral orifices 11 is released while the other 12 remains isolated by the mask. Consequently, the withdrawn gas is diverted from the annular 9 to the center of the central tube 10.

If this device effectively contributes to the security of storage during the operating phase by sealing the annular 9, it nevertheless has several drawbacks. On the one hand, it is inherent in known systems to reduce the passage section of the withdrawn gas, the section of the central tube cumulated with that of the annular being limited at the outlet to that of the central tube. In other words, above the safety valve, only part of the internal section of the well 2 is used, which increases the pressure losses in the corresponding gas flow as well as its flow speed. On the other hand, the elements comparable to the mask 40 described above, because they take place within the central tube and clutter its passage section, further accentuate these pressure drops. They also help to hinder the introduction of downhole tools or the withdrawal of tubing. Different elements used to close the ring finger during the operating phase have also been devised which do not fit into the central tube to partially plug it. They then have other drawbacks such as the need to offset the central tube with respect to the axis of the well, to provide safety valves of small size in order to place them directly in the ring finger, to risk suddenly detaching of the casing under the effect of internal pressure or to be irremovable ...

US-A-3,008,522 describes a device allowing, in a well in operation, the circulation of two different fluids, in a central tube and in an annular space, means allowing a determined level to pass a fluid from the central tube towards the ring finger, while the other fluid passes from the ring finger into the central tube. The means described form restrictions on the circulation of fluids, in particular in the central tube.

This is how the present invention aims to authorize an optimal implementation of both "dewatering" and the actual operation of the well while allowing, in order to ensure safety during the operation phase. , easy recourse to means known as valves of the normally closed type of current size. And this goal must be achieved without the disadvantages listed above manifesting themselves.

For this is proposed here a safety sleeve for wells communicating in particular with an underground reserve of pressurized fluid, a peripheral tube being disposed in said well as well as a central tube concentric with said peripheral tube so that an annular is defined therebetween , characterized in that said sleeve is constituted by a hollow cylinder having upper ends and lower as well as inner and outer lateral surfaces, said sleeve being adapted to be connected, at said outer lateral surface, to said peripheral tube and, at said lower lateral surface, to said central tube, an annular groove being formed in said lower lateral surface for receiving a plug and conduits adapted to put said annular in communication with said central tube, a first series of said conduits starting from said upper end of said cylinder to end at said inner lateral surface between said groove and said lower end of said cylinder while a second series of said conduits starts from said lower end of said cylinder to end at said inner lateral surface between said groove and said upper end of said cylinder.

For example, the hollow cylinder is thick-walled while each of said conduits has a portion pierced longitudinally in the wall of said cylinder and extending by a bend in an oblique portion. According to a first advantageous embodiment, each of said conduits is locally of cylindrical section, said conduits being preferably distributed circumferentially at equal distance from each other. There are then for example a total of eight conduits, each of said series having four immediately adjacent to each other. According to a second advantageous embodiment, each of said series of conduits is formed by the envelope of parallel cylindrical channels arranged so that two neighboring channels interpenetrate.

Advantageously, said cylinder constituting said sleeve is machined in a steel billet. It can also be forged. Likewise, it preferably admits a height of between approximately 1.5 m and approximately 3 m.

The present sleeve then forms part of a safety assembly which, according to the invention, further comprises a length of central tube constituted by an upper piece connected to said upper end of said sleeve and by a lower piece connected to said lower end of said sleeve, at least said lower piece being provided with a safety valve capable of closing off said central tube in the event of an accident.

Advantageously, said length of central tube is of the order of ten meters. Likewise, a plug seat is preferably provided on each of said pieces of said length of central tube in the immediate vicinity of said sleeve.

If said upper piece of said central pipe length rather ends in a flare, said lower piece of said central pipe length finds advantage to end with an inner annular groove, another plug seat being disposed between said safety valve and said groove.

Advantageously, said safety valve is of the withdrawable type normally closed. It can take place around said length of central tube and include a control line for the supply of a hydraulic fluid which is held in place by virtue of its partial housing within said sleeve.

In one embodiment of the safety assembly, the outer lateral surface of said sleeve is provided with O-rings to seal between said sleeve and the peripheral tube.

In another embodiment, the security assembly rather has a length of peripheral tube that is little different from said length of central tube and likewise consists of an upper piece connected to said upper end of said sleeve and by a lower piece connected to said lower end of said sleeve. When said peripheral tube is a protective tube taking place within a cemented casing, said upper piece of said length of protective tube then preferably comprises an orifice for the passage of said control line, means being provided in order to '' sealing said orifice.

According to the invention, a method of operating a well communicating in particular with an underground reserve of pressurized fluid, a peripheral tube being disposed in said well as well as a central tube concentric with said peripheral tube so that an annular is defined between them, is characterized in that it implements the present safety assembly so that the flows established on the one hand in the central tube and on the other hand in the annular are able to cross.

According to a first embodiment, a first operation of the present method consists in connecting said security assembly to said central and peripheral tubes, said upper piece of said length of central tube also being provided with another security valve capable of closing off said central tube in the event of an accident.

When said underground reserve is constituted by a cavity leached in the rock salt initially filled with brine and when said reserve fluid is a gas, an intermediate operation of the present process then consists in filling said cavity with said gas, said gas being introduced under pressure by said central tube above said sleeve, then passing through said annular below said sleeve to pushing back said brine which rises through said central tube below said sleeve and is recovered by said annular above said sleeve.

Still in the same embodiment, a last operation of the present method consists in withdrawing said fluid from the surface or / and injecting it into said underground reserve by both said central tube and said annular.

• a) la première opération du présent procédé évoquée plus haut consiste en outre, à disposer dans le puits:
  • le tube périphérique de sorte qu'une extrémité inférieure se trouve au-dessus de la couche productrice supérieure, un premier bouchon annulaire étant disposé autour de l'extrémité inférieure du tube périphérique pour boucher l'espace entre le tube périphérique et la paroi revêtue ou non du puits,
  • le tube central à l'intérieur du tube périphérique de sorte qu'une extrémité inférieure du tube central se trouve entre la couche productrice supérieure et la couche productrice inférieure, un second bouchon annulaire étant disposé autour de l'extrémité inférieure du tube central pour boucher l'espace entre le tube central et la paroi revêtue ou non du puits ; tandis qu'
• b) une opération ultérieure d'exploitation proprement dite, consiste à faire passer
  • au bas du puits, les hydrocarbures provenant de la couche productrice inférieure dans le tube central et ceux provenant de la couche productrice supérieure dans l'annulaire ;
  • en haut du puits, les hydrocarbures provenant de la couche productrice supérieure dans le tube central et ceux provenant de la couche productrice inférieure dans l'annulaire ;
  les hydrocarbures des deux couches se croisant au sein du manchon.

When said reserve comprises an upper hydrocarbon producing layer and a lower hydrocarbon producing layer, an exploitation well crossing the two producing layers and having a wall coated or not at the right of the two layers so that the hydrocarbons of the two layers can enter the well:

• a) the first operation of the present process mentioned above also consists in placing in the well:
  • the peripheral tube so that a lower end is located above the upper producing layer, a first annular plug being arranged around the lower end of the peripheral tube to block the space between the peripheral tube and the coated wall, or not from the well,
  • the central tube inside the peripheral tube so that a lower end of the central tube is between the upper producing layer and the lower producing layer, a second annular stopper being arranged around the lower end of the central tube for sealing the space between the central tube and the wall, whether coated or not, of the well; wheras'
• b) a subsequent operating operation proper, consists in passing
  • at the bottom of the well, the hydrocarbons coming from the lower producing layer in the central tube and those coming from the upper producing layer in the ring finger;
  • at the top of the well, the hydrocarbons coming from the upper producing layer in the central tube and those coming from the lower producing layer in the annular;
  the hydrocarbons of the two layers crossing each other within the sleeve.

We note the rusticity of all the equipment put in place during the first operation. It is then recommended to ensure that the space between the peripheral tube and the wall, whether coated or not, of the well is chosen to be as small as the operations for installing the peripheral tube allow and that the safety valves have a body taking place around the central tube to which they are subject. Thus, in fact, the maximum passage sections are obtained for the separate ascent of the two kinds of hydrocarbons.

In an annex, note the possibility that the wall of the well is coated with a casing provided with perforations in line with the hydrocarbon-producing layers and / or that a retaining liquid retained by the first annular plug is disposed between the casing and the peripheral tube.

According to another embodiment of the present method, a first operation of the said method consists in connecting the said security assembly to the said central and peripheral tubes, a jacket being applied in leaktight manner against the said inner lateral surface of the said sleeve so that the said conduits are closed, said plug being also removed, a subsequent operation of said method consisting of withdrawing from the surface said fluid in reserve or / and injecting into said underground reserve by said central tube only.

Advantageously, during the operation of connecting said safety assembly, said assembly is disposed 30 meters below the ground surface, or even more if this is deemed necessary. However, it being understood that said well further comprises a cemented casing terminated below by a shoe, and that said peripheral tube consists of a protective tube taking place within said cemented casing, during the operation of connecting said assembly of security, said assembly is rather disposed about 10 meters above said shoe of said well.

Still during this same operation of connecting said security assembly, upper sections of central tube are preferably provided with seals and fitted into said upper piece of said length of central tube of said security assembly while lower sections of central tube are instead secured within said lower piece of said length of central tube of said safety assembly via anchor dogs and an inflatable bladder so that said lower and upper sections can be removed at any time without having to undo said connection of said security assembly.

In other words, as soon as the present sleeve is disposed within the tube system of the well, its plug being in place and its conduits cleared, it realizes a bypass of the fluid flow from the ring finger to the central tube and from the fluid flow from the central tube to the annular, the two corresponding flows therefore being caused to cross. This has the advantage that each of the two flows passes through the central tube. Thanks to two safety valves mounted on this tube, one installed below the sleeve and the other above, the closure of any passage between the underground reserve and the surface is thus guaranteed in case of need.

This result is obtained without the consideration of the drawbacks of the prior art. The flows do not in fact have to undergo excessive pressure losses when passing the sleeve, the conduits of which can be made relatively wide (and in any case wider than the lateral orifices 11 and 12 of the known device described above) . The flow velocities are likewise more favorable. We note that the central and peripheral tubes remain concentric. In addition, the possibility of placing the safety valves only on the central tube allows the use of common type valves, not demonstrating a particularly small footprint. Finally, nothing narrows the passage within the central tube. And it is enough to remove the plug taking place within the sleeve to have an almost full section and to descend by the central tube any necessary tool.

Still other advantages are to be noted in relation to the nature of the fluid reserve. If it is a leached cavity in rock salt, the present sleeve is preferably put in place from the "dewatering" phase. In the operating phase, it then authorizes the withdrawal and recovery of the fluid in reserve by both the central tube and the ring finger. In other words, the cross section of the outlet fluid is increased, compared to the prior art, by the section of the annular. This amounts in practice to a doubling of section which further contributes to reducing the pressure losses and to improving the flow rates for a given flow rate.

However, the present security assembly also accommodates an oil deposit by adapting to both an injection and an exploitation well, that is to say a withdrawal. In this case, it is interesting first of all in "double completion" operations.

In the field of petroleum production, the term "double completion" is commonly used in relation to deposits comprising two geological layers containing hydrocarbons, separated by at least one impermeable layer. Whether the hydrocarbons are then in the gas phase, in the liquid phase or even in the form of an oil-gas mixture, the "double completion" technique aims to recover them on the surface without contact between the fluids from each of the layers.

The method implemented so far consists in using a production well passing through the two layers. Its casing is then pierced with perforations at the right of each of the two producing layers. In addition, two production tubes communicating with the surface and each provided with a safety valve are placed next to each other in the well. The first of them is for example shorter and stops opposite the upper perforations. The second extends to the lowest perforations and advantageously has a slight bend in order to make up for a more central position in the casing of the well as soon as the lower end of the first tube is exceeded. The system is finally supplemented by two shutters arranged between the casing and the tubes in order to force the hydrocarbons to flow within the latter. One of these shutters is located rather at the depth of the intermediate impermeable layer. Its shape remains simple, to plug the annular space between the second tube and the casing. The other, on the contrary, is of a more complex structure since, being located above the upper producing layer, it must provide insulation while allowing passage to the two tubes.

This is one of the major drawbacks of the traditional "double completion" operating process. The corresponding shutter, called in the double shutter profession, is in fact of a relatively sophisticated design. And it follows, in addition to a cost much higher than that of a simple annular shutter, a more delicate implementation. Other drawbacks are more directly linked to the tubes. In particular, placing them side by side is always a difficult operation. It is also understood that the passage section thus offered to the fluids from the two producing layers remains relatively small compared to the total section available in the casing in particular. The present method avoids the drawbacks of the prior art which have just been highlighted.

Then, this security package can be of great service in terms of security. In fact, the operators are able to choose to place it near the bottom of the well, that is to say in a place of least vulnerability in terms of both natural geological disorders and possible sabotage. They can also dismantle all or part of it and reassemble the elements to be inspected or repaired. Of course, these advantages are added to that of the notable increase in the passage section at the outlet of the well. As soon as it is a well for exploitation of the deposit, this suggests the possibility of reducing the number of wells with the enormous financial savings that this represents.

Finally, thanks to the application of a jacket within the sleeve to close off its conduits, its plug also being removed, the tube system finds itself in a situation similar to that of the prior art in the operating phase. However, the advantage of a safety valve mounted around the central tube and not inside the latter remains, also releasing its full section for the passage of the fluid. This aspect can also be combined with a particularly small ring finger whenever other considerations on flow allow. In this case, the present sleeve simply acts as a shutter for the ring finger. However, it remains particularly effective in this role since it is an integral part of the well tubes and therefore cannot be detached from it.

The present invention will be better understood on reading the detailed description which follows and on examining the appended drawings which represent, by way of nonlimiting examples, embodiments of the present sleeve as well as of the present safety assembly. comprising. They also illustrate embodiments of the present method of operating a well communicating with an underground reserve of fluid.

• la figure 1 est une coupe verticale très schématique d'un massif de sel gemme et d'une cavité de stockage lessivée dans ce massif ;
• la figure 2 est une coupe similaire à la précédente. Elle comporte toutefois deux coupures semi-horizontales, une partie du massif au niveau de chacune de ces coupures n'étant pas représentée si bien qu'une échelle bien plus grande peut être utilisée. Les mouvements de fluides en phase de "dewatering" y sont représentés à l'aide de flèches ;
• les figures 3 et 4 sont des demi-coupes axiales d'un puits et de ses tubes comportant un dispositif de sécurité conformément à l'art antérieur. Ce dernier est représenté dans sa configuration déployée en phase de "dewatering" sur la figure 3 et dans sa configuration repliée en phase d'exploitation proprement dite du puits sur la figure 4 ;
• les figures 5 et 6 se rapportent à un manchon de sécurité conformément à la présente invention. En coupe axiale sur la figure 5, il est montré sur la figure 6 en coupe transversale dans le plan I-I de la figure 5 ;
• les figures 7 et 8 sont des coupes axiales de deux formes de réalisation avantageuses d'un ensemble de sécurité conformément à la présente invention ;
• les figures 9 et 10 replacent l'ensemble de sécurité de la figure 7 dans le contexte d'un puits montré en coupe axiale. Elles illustrent respectivement les phases de "dewatering" et d'exploitation proprement dite; et
• la figure 11 est une coupe schématique d'un puits de production de pétrole en "double complétion" dans lequel est mis en oeuvre un mode de réalisation du présent procédé.

In these drawings:

• Figure 1 is a very schematic vertical section of a rock salt mass and a leached storage cavity in this mass;
• Figure 2 is a section similar to the previous one. However, it has two semi-horizontal cuts, a part of the massif at each of these cuts is not shown so that a much larger scale can be used. Fluid movements in the dewatering phase are represented using arrows;
• Figures 3 and 4 are axial half-sections of a well and its tubes comprising a safety device according to the prior art. The latter is shown in its configuration deployed in the "dewatering" phase in FIG. 3 and in its folded configuration in the actual operating phase of the well in FIG. 4;
• Figures 5 and 6 relate to a safety sleeve according to the present invention. In axial section in Figure 5, it is shown in Figure 6 in cross section in the plane II of Figure 5;
• Figures 7 and 8 are axial sections of two advantageous embodiments of a security assembly according to the present invention;
• Figures 9 and 10 replace the safety assembly of Figure 7 in the context of a well shown in axial section. They respectively illustrate the "dewatering" and exploitation phases proper; and
• Figure 11 is a schematic sectional view of a "double completion" oil production well in which an embodiment of the present process is implemented.

Figures 5 and 6 show a safety sleeve 100 in accordance with the present invention. It is indeed a thick-walled cylinder that can reach 1.5 to 3 meters in height, for example machined from a steel billet or forged. The outside diameter of the sleeve corresponds more or less to that of the protective tube (peripheral tube) to be accommodated by the well. Threads 132 in order to allow the connection of the sleeve to this tube are for example made. In the axial section of FIG. 5 it appears that a lower thread 132b can be directly provided on the external surface of the sleeve while an upper thread 132h can be formed inside a crown projecting axially from the sleeve. Likewise, the internal diameter of the sleeve is chosen so that the central tube 10 can be connected in leaktight manner within its internal hole 110. Threads 112b lower and 112h upper are for example made for this purpose on the surface of the hole 110 inside around each of the ends of the sleeve 100.

In addition to the features which have just been mentioned and which, for the time being, are limited to making the present sleeve a connecting piece between the different sections of the protection tube 30 as well as of the central tube, other characteristics confer the qualities of a derivation allowing the crossing of fluid flows. These are first of all a groove 111 formed on the surface of the hole 110 inside the sleeve 100, approximately halfway up the latter. This groove 111 is in fact adapted to serve as a seat for a plug 60 shown in FIG. 7 and which seals the hole 110 in a sealed manner. In this way, the passage offered by the central tube 10 is interrupted at the level of the sleeve. 100, possibility of which we will see the interest in the following paragraphs. Then, conduits 131 are drilled in the same wall of the cylindrical sleeve 100. Each of them has a longitudinal part which starts from the transverse surface of the wall of the sleeve, that is to say more simply from one of its ends. In other words, they are designed to communicate with the annular 9 as soon as the sleeve 100 is mounted between its respective sections of protective tube 30 and central tube 10. The longitudinal part is extended by a bend in an oblique part 113 which finally opens into the hole 110 inside the sleeve. As soon as the sleeve 100 is connected to the tubes, the conduits 131 consequently communicate with the central tube 10. They therefore connect the ring finger 9 and the interior of this tube 10.

The straight longitudinal parts of the conduits may be cylindrical and distributed circumferentially at equal distance from each other as shown in solid lines on the axial and transverse sections of Figures 5 and 6 respectively. Their number is adaptable according to the diameter of each conduit, the thickness of the wall of the sleeve, the desired flow rates, etc. Figures 5 and 6 show eight, but they could just as easily be four or less. It is conceivable, on the contrary, to multiply them to the point that the various conduits interpenetrate and form a common passage between them. This is what is shown in Figures 5 and 6 in dotted lines. However, there is no question of connecting all the conduits together. Indeed, a first series of conduits (half in the figures) is provided to open above the plug seat 111 (cf. sections 131h and 113h) while a second series formed by the remaining conduits opens under the seat 111 (see sections 131b and 113b). In the cross section of FIG. 6, all the conduits 131 h of the first series are drawn next to each other. They are therefore made in the same half-sleeve (if we imagine to cut the overall cylinder according to a diameter). The conduits 131b of the second series are, in turn, made in the other half-sleeve.

Figure 7 replaces the sleeve 100 which has just been described in the context of the protective tubes 30 and central 10 to be connected to it. The latter are however represented very schematically. In particular, the details of the fittings by thread or even by interlocking are not reported. Likewise, the connections between the various pipe sections are not shown. However, their existence remains in the mind of those skilled in the art, so that we will not discuss them here any more. What should be retained from FIG. 7 illustrating a preferred safety assembly in accordance with the present invention essentially relates to a particular length 13 of the central tube 10 as well as a length 33 of the protection tube 30 which completes the sleeve to ensure the safety of the well.

As for the length 13, it is made up of two pieces 13b and 13h, which are more or less similar and which come to adapt on either side of the sleeve 100. Moving away from the latter. , we find identically on each of these two pieces: a plug seat 15, then a safety valve 50. In FIG. 7, the mention "b" (for bottom) following the reference number makes it possible to distinguish the comparable elements of piece 13b and the mention "h" (for top), those of piece 13h. While the plug seats 15 are not absolutely necessary, the valves 50 are advantageously valves of the type removable normally closed; that is to say that in the absence of oil arrival by the control lines 51, the valves 52 of the valves 50 close and thus interrupt the passage within the central tube 10. In this case, valves whose body 53 is arranged externally around the central tube 10 can easily be used with the interesting clearance of space within the tube 10 that this implies (in order to authorize the descent or the ascent various tools). These valves 50 need not be particularly space-saving. They can optionally be installed with the cable in a known manner around the piece 13 of tube 10. However, it is rather necessary to design the security assembly comprising sleeve 100, pieces 13 of central tube 10 and pieces 33 of protective tube 30 as a all assembled on the surface to then be freely placed in the well or removed from the latter.

As for the free ends of the two pieces 13b and 13h, they are rather of distinct diameters, the upper piece 13h ending for example by a slight flaring 17 while the lower piece 13b does not change size. The latter is optionally provided with a terminal annular groove 16. In this way, the length 13 is able to be mounted within the central tube 10 while allowing easy disassembly regardless of the part of the tube 10 to be removed. The details of the corresponding connections are however given below with reference to FIG. 8. In FIG. 7, finally, it appears that another plug seat 14 is also provided a little above the lower end of the piece 13b. This seat 14 as well as the seats 15 previously mentioned are arranged so that, the corresponding plugs once in place, the tube sections are insulated. The tightness and mechanical strength of each of these sections can then be tested separately using different tests familiar to those skilled in the art.

Finally, note with regard to the structure of this security assembly that the length 33 of associated protective tube 30 also consists of a piece 33h upper and a piece 33b lower between which is the present sleeve 100. The pieces 33 have for example a length comparable to that of the pieces 13 that they protect respectively. Their only particularity is to include an orifice for the passage of the lines 51 for controlling the valves 50. As this orifice must also be sealed, it is advantageous for the two lines 51 h and 51 b of each of the two safety valves 50 to use the same path. For this purpose, the line 51h of the upper valve 50h is preferably diverted towards the sleeve 100. The lines 51 partly housed in the latter are also less likely to break due to excessive movement within the ring finger 9 .

The security assembly thus formed can reach a total length of the order of a few tens of meters. A priori, it is able to be placed in the well at any level between the surface and the shoe. Two places referenced respectively 4h and 4b in Figure 1 are more advantageous. These are, on the one hand, approximately 30 meters below the surface and, on the other hand, approximately 10 meters above the hoof. Between these two positions, the deeper is even more interesting since it puts the safety assembly out of reach of many causes of damage in the well, for example earthquakes, surface explosions or readjustments of land following settlement or other geological phenomena occurring in the longer term.

Figure 8 relates to another embodiment of this security assembly. There is the sleeve 100 and the pieces 13b and 13h of central tube 10 arranged in the extension of the inner side surface of the latter. If necessary, sleeve 100 and pieces 13 are therefore formed in one piece. The variant in fact concerns the external lateral surface of the sleeve. Rather than pieces 33 of protection tube 30 arranged in an extension, this time it includes gaskets 34, in particular toric seals. In FIG. 8, there are two at each end of the sleeve 100. Their function is to ensure sealing with the protection tube 30 in which the safety assembly thus formed is engaged.

This provides an even easier to set up security package. Provided that the protective tube 30 has a suitable internal shoulder 35, it provides support for the assembly which is thus well maintained. Above it, it is advantageous for the protective tube 30 to be less adjusted to the external lateral surface of the sleeve in order to facilitate its descent to its final place.

Figures 9 and 10 illustrate precisely how the security assembly which has just been described is advantageously implemented when it is disposed in position 4b, near the shoe 21 of the well. The assembly is in fact easily recognizable with its sleeve 100 within which the central plug 60 is subject - the seal being ensured by stages of O-rings 62 (cf. FIG. 7) -, its pieces 13h and 13b of tube 10 central receiving the safety valves 50 as well as its pieces 33h and 33b of protection tube 30. If the upper piece 33h of the latter is completed up to the surface, the lower piece 33b is on its side adapted to end with a narrowing 34 which allows it to fit within an annular shutter 70. The tightness of the socket is guaranteed by various stages of seals interposed between the narrowing 34 and the shutter 70. This other part is as for it provided in a conventional manner inside the casing 20 of the well at some distance above its shoe 21. It consists of a longer length of tube, wider and which is tightly fixed to the casing 20 using the annular plug 31 intended to retain the liquid 32 for completion. Then comes a converging length which continues in a barely narrower guide than the central tube 10 and comprising two plug seats 71 and 72. These make it possible to place plugs so that the tightness and mechanical strength of the protective tube 30 can be tested or that the bottom of the well is if necessary isolated from the cavity 1.

In addition to the elements which have just been mentioned and which alone are present in the configuration of FIG. 10, FIG. 9 shows upper and lower sections 10h and 10b of the central tube 10 sandwiching the length 13 of tube 10 of the this security package. The upper 10h sections take place within the terminal flaring 17 of the upper 13h piece. The corresponding nesting is carried out within, for example, O-ring seals so that the seal of the connection is guaranteed. The lower sections 10b engage in turn in the right end of the lower piece 13b and are fixed there using anchor dogs. An inflatable bladder 18 or other O-rings interposed between the facing pipes allow, if necessary, to ensure perfect sealing despite the relatively large difference in diameters. This difference is indeed advantageous; because, as soon as the bladder 18 is deflated, the operator can raise one or more of the lower sections 10b through the length 13 of central tube 10 (of course by removing the plug 60).

Preferably located lower than the annular shutter 70 on the central tube 10, there is a safety seal 19. Its role is to make possible the release within the cavity 1 of the rest of the central tube 10 which, in the "dewatering" phase at least, extends to the bottom of the cavity. This release can occasionally be ordered from the surface or even intervene automatically in the event, for example, of excessive stress on the tube (due to the fall of rocky blocks, etc.). Thus the tube system of Figure 9, representative of that used during "dewatering" leads to flows indicated by continuous arrows for brine B and dashed lines for gas G. It immediately appears that at level of the sleeve 100, the brine B is derived from the central tube 10 towards the annular 9 and that, likewise, the gas G is derived from the central tube 10 towards the annular 9, but flowing in the direction reverse of brine.

In the operating phase which is the subject of FIG. 10, it is then possible to remove the upper sections 10h and lower 10b from the central tube 10. The gas G is evacuated beyond the annular shutter 70 both by the central tube 10 and by the annular 9. After the passage of the sleeve 100, the evacuation by the two passages, tube 10 and annular 9, is continues. If, moreover, an accident leads to the closing of the valves 50, all communication between the interior of the repository and the surface is interrupted. Indeed, the lower valve 50b cuts the flow in the central tube 10 below the sleeve, that is to say in the annular 9 above. The upper valve 50h for its part cuts off the flow within the central tube 10 above the sleeve. Beyond this last valve, no more gas therefore passes more.

Another way of implementing the present security assembly during the operating phase consists, for example, first of all in removing from the latter the valve 50h of higher security. Likewise, the plug 60 is removed. Then a shirt adapted to take place in the hole 110 inside the sleeve 100 is lowered so as to be applied against the mouth of the oblique parts 113 of the conduits 131. As long as the application of the shirt is sufficiently tight, any communication of the tube 10 central with the ring finger 9 is thus prevented. And all of the gas G finally flows through the central tube 10 to the surface. The lower valve 50b left in place on the safety assembly is therefore able to interrupt this flow in the event of an accident.

This mode of use of the present sleeve, which a priori brings it closer to known safety devices such as that of FIGS. 3 and 4, remains however advantageous from the point of view of the passage sections. It in fact makes it possible to have the single valve outside the central tube within which the flow is therefore not impeded locally. In addition, the sleeve then used can have a particularly thin wall. In other words, it is possible in this case to minimize the section of the ring finger. And it is as much gained for the central tube as well vis-à-vis the flows as in the circulation of various tools.

Those skilled in the art will no doubt find other embodiments of the present method of operating a well which, expressed more generally, consists in allowing the flows in the central tube, on the one hand, and in the ring finger, on the other hand, to cross. In the previous example of the leached cavity in rock salt intended to contain a gas in reserve, the crossing of two distinct fluids is rather carried out in phase of "dewatering" while, during the exploitation, gas goes up by the central tube as well as possibly by the ring finger. However, other applications can be envisaged, such as with withdrawal or injection wells for oil deposits. Although in this case the same fluid, hydrocarbons or water, can circulate in the two intersecting flows, the passage in turn of the two flows in the central tube allows their respective shutdown thanks to valves exclusively mounted on this tube . It is also possible to force all the fluid to pass through the central tube by closing the conduits of the sleeve and by removing its plug, a single valve mounted on this same tube then being sufficient. In all cases, a wider passage section is offered to the fluid compared to the prior art. To further enlarge it, it is not finally excluded to dispense with a protective tube 30 and to directly connect the present sleeve 100 to the cemented casing 20. The following claims therefore speak of a peripheral tube to designate either the protective tube, the association of the latter with the cemented casing or even a production tube disposed around the central tube.

FIG. 11 finally presents a block diagram of another embodiment of the present method. It is developed in particular as part of a "double completion" operation. For this, a vertical axis I-I has been postponed which corresponds to the axis of rotation of an oil exploitation well shown in longitudinal section. This crosses a deposit comprising in particular two layers 210, 220 rich in hydrocarbons separated by a waterproof layer 200. In the drawing, these layers are sketched on either side of the well in the form of sub-horizontal bands. Even if the hydrocarbons which they contain respectively are identical, distinct symbols mark them in the figure: dashes for those of the upper layer 210 and dots for those of the lower layer 220. Two straight lines slightly inclined on the horizontal and located between the two layers symbolize a section to indicate, moreover, that they are distant by a priori any height.

This is how the fluid content of each of the two layers enters the well. For this purpose, the casing 20 of the latter is for example provided with perforations 21 (resp. 22) in line with the layer 210 (resp. 220). There may also be no casing at all at the bottom of the well. This is particularly the case in hard rock. So that there is no contact between the hydrocarbons of the two layers during their ascent within the well, the present invention provides for having two concentric production tubes there.

The inner tube, rather called hereinafter central tube, descends beyond the upper producing layer 210 to the right of the impermeable layer 200. From then, its lower end should be opposite a part of the casing 20 devoid of perforations, and this over a sufficient height for an annular obturator 11, interposed at this location between the central tube 10 and the casing 20 , effectively prevents the hydrocarbons of the upper layer 210 from penetrating inside the central tube 10. Those coming from the lower layer 220 are then on the contrary free to rush into it (in particular under the effect of the pressure prevailing within the layer).

In the following paragraphs, the outer tube will be called peripheral tube 30. The space 32 separating it from the casing 20 is often filled with a relatively dense liquid. An annular shutter 31 disposed in the space 32 then makes it possible to retain this liquid. Its role is to relieve the casing by exerting on it a radial support force. As illustrated in FIG. 11, the annular obturator 31 is arranged in accordance with the invention above the upper perforations 21 of the casing 20. It then encloses the lower end of the peripheral tube 30 so that the hydrocarbons coming from the upper layer 210 rise (also under the effect of their own pressure) inside this last tube. The presence at this depth of the longer central tube 10, however, obliges them to flow only in the annular 9 between the two concentric tubes.

In the context of the invention, these tubes are further provided with a safety assembly as described above. Without giving here again all the construction details, we recall its general structure. First of all, it comprises a sleeve 100 in the form of a cylinder a few meters high and with a thick wall. Its internal diameter is chosen so that the central tube 10 is connected to it so that the internal surface of the sleeve 100 forms with it a single central pipe 110. In service, however, this central pipe 110 is closed with a plug 60 taking place in the sleeve 100 halfway between its upper and lower ends.

The outside diameter of the sleeve 100 is on its side chosen so that the peripheral tube 30 is connected to it so that the outside surface of the sleeve 100 forms with it a continuous intermediate space 32. It follows that the thickness of the sleeve 100 coincides more or less with the ring finger 9 between the two concentric tubes. The latter is not thereby blocked, because longitudinal ducts 131 are drilled there.

A first series of these conduits starts from the upper end of the sleeve 100 and, by a bent part 113, ends at its inner surface below the plug 60. A second series of these conduits starts inversely from the lower end of the sleeve 100 and likewise ends at its inner surface, but this time above the plug 60. In other words, the crossing of the flows established respectively in the central pipe 110 and in the annular 9.

The interest of this crossing appears as soon as we examine the other components of the safety assembly used here. These are indeed pieces 13h and 13b of central tube 10 secured relatively above and below the sleeve 100 and around each of which is fixed the body 53 of a safety valve 50. With valves 52 inside the central pipe 110, these valves can be of the standard type, called "normally closed", rather removable so as to be installed in particular on the cable. Pieces 33h and 33b of peripheral tube 30 also take place around the pieces 13. The safety assembly thus formed if necessary reaches a height of ten meters. It is inserted into the train of elementary tubes lowered into the well to form the two concentric production tubes. Thus if necessary (accident or put to sleep), the valves 50 are able, by closing, to stop the flows of the two kinds of hydrocarbons.

The location of the valves outside the central pipe 110, however, leaves the latter largely unobstructed. In particular, it remains possible to descend within it various downhole tools, the disassembly of the plug 60 not posing any difficulty. Furthermore, as symbolically indicated by the two inclined lines on the horizontal cutting the well under the safety assembly, the latter can be arranged at any depth. It is then chosen to place it according to security needs (vis-à-vis any sabotage for example) or relative to the activity of the well (for a more or less intermittent operation, etc.).

In addition to these advantages which, with others not mentioned here, stem moreover from the very nature of the security system selected, the "double completion" process which has just been described, presents more specific interests. On the one hand, in fact, the flow sections for each of the two hydrocarbon flows are made maximum. To be convinced of this, it suffices to note that at the bottom of the production well, the entire inner section of the peripheral tube 30 is the site of flows, the hydrocarbons of the lower layer 220 passing through the central pipe 110 and those of the upper layer 210 by the annular 9. From this point of view, it is recommended to choose the diameter of the peripheral tube 30 as large as possible taking into account the total section available in the cased well. Similarly, at the top of the well, the two kinds of hydrocarbons being however exchanged, they flow full sections. Between the two, the sleeve 100 does not really constitute a constriction of the passage insofar as the conduits 131 pierced in its wall are very numerous (for example eight in each series). Likewise, it is not the valves 50 arranged around the central tube 10 which constitute a significant obstacle to the flows. It follows that the pressure losses on the ascent of the hydrocarbons are minimized.

On the other hand, only simple shutters for sealing a ring finger are used. These are the shutter 31 isolating the support liquid 32 vis-à-vis the hydrocarbons of the upper layer and the shutter 11 isolating the two kinds of hydrocarbons. The use of double shutters is thus avoided with the additional cost that it implies.

Note that these last two advantages come from the use of concentric production tubes. This remarkable arrangement can however be envisaged here thanks to the joint use of the security assembly according to the present invention. The latter makes it possible, in fact, to stop the ascent of the hydrocarbons if necessary, and this without losing anything of the two advantages in question.

It is quite clear that this safety sleeve could render similar services in installations other than oil wells. Concentric pipes of chemical complexes in particular may find it advantageous to use them to achieve within them the crossing of flows. This is why the claims which follow, firstly attempt to protect the very structure of the sleeve. And it is only in a second time that its application to oil exploitation is claimed.

Claims (30)

1. A safety sleeve for a borehole communicating in particular with an underground reserve of fluid under pressure, a peripheral tube being disposed in said borehole together with a central tube coaxial with said peripheral tube, thereby defining an annular space between them, caracterized in that said sleeve (100) is constituted by a hollow cylinder having a top end and a bottom end and a lateral inside surface and a lateral outside surface, said sleeve (100) being adapted to be connected level with said lateral outside surface to said peripheral tube (30) and level with said lateral inside surface to said central tube (10), an annular groove (111) being formed in said lateral inside surface to receive a plug (60) and ducts (113, 131) provided to put said annular space (9) into communication with said central tube (10), a first series of said ducts (113, 131) running from said top end of said cylinder and terminating in said lateral inside surface between said groove (111) and said bottom end of said cylinder, while a second series of said ducts (113, 131) runs from said bottom end of said cylinder and terminates in said lateral inside surface between said groove (111) and said top end of said cylinder.
2. A safety sleeve according to claim 1, characterized in that said hollow cylinder is a thick-walled cylinder and in that each of said ducts (113, 131) includes a portion (131) drilled longitudinally in said thick wall of said cylinder and extended by a bend in an oblique portion (113).
3. A safety sleeve according to claim 1 or 2, characterized in that each of said ducts (113, 131) is locally cylindrical in section, said ducts (113, 131) being preferably circumferentially distributed at uniform spacing.
4. A safety sleeve according to claim 3, characterized in that there are at least eight ducts (113, 131) in all, each of said series of ducts comprising four ducts that are immediately adjacent to one another.
5. A safety sleeve according to claim 1 or 2, characterized in that each of said series of ducts (113, 131) is constituted by the envelope of parallel cylindrical channels disposed in such a manner that pairs of adjacent channels interpenetrate.
6. A safety sleeve according to any one of claims 1 to 5, characterized in that said cylinder constituting said sleeve (100) is machined in a billet of steel or is forged.
7. A safety sleeve according to any one of claims 1 to 6, characterized in that said cylinder constituting said sleeve (100) has a height lying in the range about 1.5 m to about 3 m.
8. A safety system characterized in that it comprises a sleeve according to any one of preceeding claims, together with a length (13) of central tube (10) constituted by a top portion (13h) connected to said top end of said sleeve (100) and by a bottom portion (13b) connected to said bottom end of said sleeve (100), at least said bottom portion (13b) being provided with a safety valve (50b) suitable for closing said central tube (10) in the event of an accident.
9. A safety system according to claim 8, characterized in that said length (13) of central tube (10) is of the order of 10 meters long.
10. A safety system according to claim 8 or 9, characterized in that a plug seat (15h, 15b) is provided in each of said portions (13h, 13b) of said length (13) of central tube (10) in the immediate proximity of said sleeve (100).
11. A safety system according to any one of claims 8 to 10, characterized in that said top portion (13h) of said length (13) of central tube (10) is terminated in a flare (17).
12. A safety system according to any one of claims 8 to 11, characterized in that said bottom portion (13b) of said length (13) of central tube (10) is terminated by an inside annular groove (16), with another plug seat (14) being disposed between said safety valve (50b) and said groove (16).
13. A safety system according to any one of claims 8 to 12, characterized in that said safety valve (50b) is of the normally-closed removable type.
14. A safety system according to claim 13, characterized in that said safety valve (50b) is installed around said length (13) of central tube (10) and includes a control line (51b) for conveying a hydraulic fluid, which line is held in place by virtue of being received in part within said sleeve (100).
15. A safety system according to any one of claims 8 to 14, characterized in that the lateral outside surface of said sleeve (100) is provided with ring seals (34) for providing sealing between said sleeve (100) and the peripheral tube (30).
16. A safety system according to any one of claims 8 to 14, characterized in that it comprises a length (33) of peripheral tube (30) which is substantially as long as said length (13) of central tube (10) and which is similarly constituted by a top portion (33h) connected to said top end of said sleeve (100) and by a bottom portion (33b) connected to said bottom end of said sleeve (100).
17. A safety system according to claim 16, said peripheral tube (30) being a protective tube installed within cemented casing, characterized in that said safety valve (50b) is installed around said length (13) of central tube (10) and comprises a control line (51b) for conveying a hydraulic fluid, which line is held in place by virtue of being received in part within said sleeve (100), and in that said top portion (33h) of said length (33) comprises an orifice for passing said control line (51b), means being provided to seal said orifice.
18. A method of operating a borehole in communication in particular with an underground reserve of fluid under pressure, a peripheral tube being disposed in said borehole together with a central tube coaxial with said peripheral tube such that an annular space is defined between them, characterized in that it implements a safety system according to any one of claims 8 to 17 such that flows established respectively in the central tube (10) and in the annular space (9) can intersect.
19. A method according to claim 18, characterized in that a first operation of said method consists in connecting said safety system to said central and peripheral tubes (10, 30) said top portion (13h) of said length (13) of the cenral tube (10) being likewise provided with a further safety valve (50h) suitable for closing said central tube (10) in the event of an accident.
20. A method according to claim 19, applicable to said underground reservoir being constituted by a cavity washed out from rock salt, which cavity is initially filled with brine, and applicable to said fluid in the reserve being a gas, characterized in that an intermediate operation of said method consists in filling said cavity (1) with said gas (G), said gas (G) being injected under pressure via said central tube (10) above said sleeve (100), and then passing through said annular space (9) beneath said sleeve (100), thereby pushing said brine (B) which rises via said central tube (10) beneath said sleeve (100) and is recovered from said annular space (9) above said sleeve (100).
21. A method according to claim 19 or 20, characterized in that a final operation of said method consists in removing said fluid in reserve to the surface and/or injecting said fluid into said underground reserve via both said central tube (10) and said annular space (9).
22. A method according to claim 19, applicable to said reserve including an upper hydrocarbon producing layer (210) and a lower hydrocarbon producing layer (220), the borehole being lined with a casing (20) passing through both layers (210, 220) and having a wall, lined or not, where it overlies both layers (210, 220), in such a manner as to enable the hydrocarbons in both of the layers (210, 220) to penetrate into the borehole, characterized in that the method consists in:

    a) during the first operation of said method, placing in the borehole:
       the peripheral tube (30) in such a manner that a bottom end thereof lies above the upper producing layer (210), a first annular packer (31) being disposed around the bottom end of the peripheral tube (30) to block the space (32) between the peripheral tube (30) and the wall, lined or not, of the borehole; and
       the central tube (10) inside the peripheral tube (30) in such a manner that a bottom end of the central tube (10) lies between the upper producing layer (210) and the lower producing layer, a second annular packer (11) being disposed around the bottom end of the central tube (10) to block the space between the central tube (10) and the wall, lined or not, of the borehole; and

    b) during subsequent "dual completion" operation, establishing the following flows:
       at the bottom of the borehole, a flow of hydrocarbons from the lower producing layer (220) in the central tube (10) and a flow of hydrocarbons from the upper producing layer (220) in the annular space (9);
       at the top of the borehole, the flow of hydrocrabons from the upper producing layer (210) in the central tube (10), and the flow of hydrocarbons from the lower producing layer (210) in the annular space (9);
       the hydrocarbon flows from the two layers (210, 220) intersecting in the sleeve (100).
23. A method according to claim 22, further characterized in that the space (32) between the peripheral tube (30) and the wall lined or not of the borehole is selected to be as narrow as possible compatible with the operations of installing the peripheral tube (30).
24. A method according to claim 22 or 23, further characterized in that the safety valves (50) have bodies (52) installed around the central tube (10) to which they are attached.
25. A method according to any one of claims 22 to 24, characterized in that the wall of the borehole is lined with casing (20) which is provided with perforations (21, 22) where it overlies the hydrocarbon producing layers (210, 220).
26. A method according to claim 25, characterized in that a supporting liquid is retained by the first annular packer (31) which liquid is disposed between the peripheral tube (30) and the casing (20).
27. A method according to claims 18, characterized in that a first operation of said method consists in connecting said safety system to said central and peripheral tubes (10, 30) with a liner being applied in sealed manner against the lateral inside surface of said sleeve (100) in such a manner as to close said ducts (113, 131), said plug (60) moreover being removed, with a subsequent operation of said method consisting in drawing off said fluid from the underground reserve and/or in injecting fluid into said reserve via said central tube (10) only.
28. A method according to any one of claims 19 to 27, characterized in that during the operation of connecting said safety system, said safety system is disposed at least 30 meters beneath the surface of the ground.
29. A method according to any one of claims 19 to 28, said borehole further including cemented casing terminated at the bottom end by a shoe, and said peripheral tube being constituted by a protective tube installed inside said cemented casing, characterized in that during the operation of connecting said safety system, said system is disposed about 10 meters above said shoe (21) of said borehole (2).
30. A memthod according to any one of claims 19 to 29, characterized in that during the operation of connecting said safety system, top lengths (10h) of the central tube (10) are provided with sealing rings and engaged within said top portion (13h) of said length (13) of central tube (10) of said safety system, whereas bottom lengths (10b) of the central tube (10) are attached within said bottom portion (13b) of the length (13) of the central tube (10) of said safety system via anchor pieces and an inflatable chamber (18) such that said top and bottom lengths (10h, 10b) may be withdrawn at any time without it being necessary to dismantle said connection to said safety system.

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