EP0689637B1 - Method and device for cementing a well - Google Patents

Abstract

A casing is cemented within a well bore (P) or pipe by means of a radially expandable tubular preform (1). For this purpose, a) the folded preform (1) is inserted into the well (P) or pipe down to the required level; b) the well is sealed off at the bottom of the preform (1) by means of an inflatable hydraulic retainer (4); c) a curable fluid cement is injected onto the retainer so that it surrounds the lower portion of the preform; d) the preform is gradually unfolded from the top towards the bottom to press the cement against the wall of the well or pipe along the full length of the preform; e) the preform is cured to form a casing while the cement is allowed to set; and f) the retainer (4) is deflated and withdrawn from the well or pipe.

Description

The present invention relates to a method of cementing casing inside a wellbore or a pipe. It also relates to the use of a cementing device in such a process.

The invention applies in particular to wells, in particular oil wells. Although the description which follows relates to a vertical well, it goes without saying that the invention can also be implemented in non-vertical, but deviated, or even horizontal, wells. It is also applicable to pipelines, for example to oil and gas pipelines, with a view to repairing them by fitting an internal lining.

In the field of oil drilling, a casing, or casing, - commonly designated by the English term "casing" - is a cylindrical pipe made of rigid material intended to be placed inside the well. It is fixed there by means of a cement, commonly called "slag". The presence of the casing makes it possible to have a cylindrical well, of well defined diameter, with rigid wall, which allows the passage of various tools and elements necessary for the exploitation of the well.

Currently, the casing is cemented from the base of the casing by injecting a cement into the annular space between the casing and the well. This cement is injected from the surface through the very interior of the casing (plug method) or through drill rods (cementing commonly referred to by the term "innerstring").

Unfortunately, the very principle of this method, by injection then displacement of the slag volume, does not allow the placement of the slag under satisfactory conditions in the case where the annular space available is very reduced, or even zero, it is ie when the outside diameter of the casing is close to that of the well.

Tubing has recently been proposed which is obtained from a tubular preform which is deformable by expansion in radial direction between a first state - called folded - in which its largest transverse dimension is substantially less than the diameter of the well, and a second state - said unfolded - in which it has a cylindrical shape with a diameter slightly smaller than that of the well, this preform being curable in situ (after radial expansion) to form the casing.

This type of casing, as well as its installation process, is notably described in documents FR-A-2 662 207 and FR-A-2 668 241.

The objective of the present invention is to provide a method and a use of a device for cementing a casing of this kind, by means of which the cementing can be carried out under satisfactory conditions, even if the annular space available for the cement is reduced.

• a) on introduit la préforme à l'état replié dans le puits ou dans la canalisation, et on l'y descend au niveau souhaité ;
• b) on obture le puits au pied de la préforme, par gonflage en cette zone d'un obturateur hydrauliquement déformable (obturateur du genre couramment désigné par le terme anglais "packer" dans le domaine pétrolier) ;
• c) on injecte un ciment fluide et durcissable au-dessus de l'obturateur de manière à ce qu'il vienne entourer la partie basse de la préforme, le volume de ce ciment correspondant sensiblement au volume nécessaire à la cimentation du tubage dans le puits ou dans la canalisation ;
• d) on déforme la préforme pour la faire passer à l'état déplié, cette déformation se faisant progressivement de bas en haut, de sorte que le ciment est déplacé petit à petit dans l'espace annulaire compris entre la paroi de la préforme et la paroi du puits ou de la canalisation, sur toute la hauteur de la préforme ;
• e) on provoque le durcissement de la préforme pour obtenir le tubage, et on laisse prendre le ciment ;
• f) on dégonfle l'obturateur et on le retire du puits ou de la canalisation.

This objective is achieved, thanks to the method according to the invention, by the fact that this method comprises the following steps:

• a) the preform is introduced in the folded state in the well or in the pipe, and it is lowered there to the desired level;
• b) the well is closed at the foot of the preform, by inflation in this zone of a hydraulically deformable shutter (shutter of the type commonly designated by the English term "packer" in the petroleum field);
• c) a fluid and curable cement is injected above the obturator so that it comes to surround the lower part of the preform, the volume of this cement corresponding substantially to the volume necessary for the cementing of the casing in the well or in the pipeline;
• d) the preform is deformed so as to pass it in the unfolded state, this deformation taking place progressively from bottom to top, so that the cement is gradually displaced in the annular space comprised between the wall of the preform and the wall of the well or the pipe, over the entire height of the preform;
• e) the preform is hardened to obtain the casing, and the cement is allowed to set;
• f) the obturator is deflated and it is removed from the well or the pipe.

In a preferred embodiment of the invention, the balloon is inflated from the surface, by means of a fluid which is supplied by a tube passing longitudinally and right through the preform.

• après l'injection de ciment réalisée à l'étape c) ci-dessus, on injecte un autre fluide non durcissable - dit de chasse - dont la densité est supérieure à celle du ciment, et qui vient occuper l'espace compris entre l'obturateur et l'extrémité basse de la préforme ;
• on fournit le ciment, et éventuellement le fluide de chasse, depuis la surface, par le même tube que celui qui sert au gonflage de l'obturateur, via une chemise de distribution montée à l'extrémité du tube et portant ledit obturateur ;
• lorsque le procédé est mis en oeuvre avec une préforme à paroi durcissable à chaud par polymérisation, on réalise la dilatation radiale et le durcissement de cette préforme au moyen d'un fluide chaud qui est fourni depuis la surface par le tube, via la chemise de distribution ;
• après l'étape d) on injecte un fluide dans la zone située au-dessus de l'extrémité haute de la préforme pour éliminer l'excès de ciment éventuellement présent en cette zone (et en empêcher la prise).

Furthermore, according to a certain number of additional non-limiting characteristics of the invention:

• after the cement injection carried out in step c) above, another non-hardening fluid - said flush - is injected, the density of which is greater than that of the cement, and which occupies the space between the shutter and the lower end of the preform;
• the cement, and optionally the flushing fluid, is supplied from the surface, by the same tube as that which is used for inflating the obturator, via a distribution jacket mounted at the end of the tube and carrying said obturator;
• when the process is carried out with a preform with a wall which can be hardened by polymerization, the radial expansion and hardening of this preform are carried out by means of a hot fluid which is supplied from the surface by the tube, via the jacket distribution;
• after step d) a fluid is injected into the zone situated above the upper end of the preform to eliminate the excess cement possibly present in this zone (and to prevent it from setting).

The use of a device for cementing a casing in a process as described above, which is also part of the present invention, comprises a tube for supplying fluids passing right through the preform and the l he low end is connected to an inflatable hydraulic shutter.

In a preferred embodiment, the device is provided with a fluid distributor jacket, into which opens the lower end of the tube.

Advantageously, this distributor jacket constitutes a multi-way valve making it possible to selectively communicate the fluid supply tube with the interior of the shutter, with the exterior, and with the interior of the preform.

In one possible embodiment, the dispenser liner has pressure chambers the outlet of which can be closed off by balls which are put in place during operation, via the fluid supply tube.

In an advantageous embodiment, the fluid supply tube is provided with a valve located above the high end of the preform, this valve serving to degrade the excess cement, as has been mentioned more high.

Other characteristics and advantages of the invention will appear from the description and the appended drawings, which represent a preferred embodiment.

• la figure 1 est une vue générale schématique du dispositif, celui-ci étant introduit à l'intérieur d'un tube de forage ;
• la figure 2 est une vue en coupe longitudinale de la chemise distributrice et de l'obturateur hydraulique ;
• les figures 3, 3A, 3B, 3C, 3D et 3E sont des vues générales schématiques analogues à celles de la figure 1, à plus petite échelle, qui illustrent les différentes étapes principales d'une opération de cimentation du tubage à l'intérieur du puits ;
• les figures 4 et 4A sont des vues représentant le mode d'attache de la chemise distributrice (et de l'obturateur hydraulique) à la partie basse du tubage, respectivement avant et pendant leur enlèvement hors du tubage ;
• la figure 5 est une vue similaire à la figure 4, représentant les moyens de liaison du tube d'amenée des fluides avec la partie haute du tubage, les demi-vues de gauche et de droite de cette figure correspondant à l'état de ces moyens, respectivement avant et après enlèvement du tube ;
• les figures 6, 6A, 6B, 6C, 6D et 6E sont des vues similaires à la figure 2, à plus petite échelle, qui représentent la tête distributrice au cours des principales étapes de mise en oeuvre du procédé ;
• la figure 7 est un diagramme représentant la valeur des pressions mises en jeu en fonction du temps, au cours de l'opération.

In these drawings:

• Figure 1 is a general schematic view of the device, it being inserted inside a drill pipe;
• Figure 2 is a longitudinal sectional view of the distributor jacket and the hydraulic shutter;
• FIGS. 3, 3A, 3B, 3C, 3D and 3E are schematic general views similar to those of FIG. 1, on a smaller scale, which illustrate the different main stages of a casing cementation operation inside the well;
• Figures 4 and 4A are views showing the method of attachment of the distributor jacket (and the hydraulic shutter) to the lower part of the casing, respectively before and during their removal from the casing;
• Figure 5 is a view similar to Figure 4, showing the connecting means of the fluid supply tube with the upper part of the casing, the left and right half views of this figure corresponding to the state of these means, respectively before and after removal of the tube;
• Figures 6, 6A, 6B, 6C, 6D and 6E are views similar to Figure 2, on a smaller scale, which show the dispensing head during the main steps of implementing the method;
• FIG. 7 is a diagram representing the value of the pressures brought into play as a function of time, during the operation.

In FIG. 1, the ground surface has been designated by the reference S , and by the reference P the wall of a wellbore, of approximately cylindrical shape, with a vertical axis.

The cementing device shown in this figure, which is housed inside the well, essentially comprises a deformable tubular preform 1 carried by a tube 2 which passes right through it, a distribution jacket 3 disposed at the base of the preform, and an inflatable hydraulic shutter 4, disposed at the base of the jacket 3.

The assembly is suspended from a pipe 20, the latter being for example a flexible pipe unwound from a reel carried by an apparatus located on the surface.

There has been designated by the reference 21 a connecting element between the piping 20 and the tube 2, by the element 22 a connecting sleeve between the tube 2 and the upper end part of the preform. The sleeve 22 is provided with a calibrated relief valve 23 (ball valve), the role of which is to make the interior of the preform communicate with the outside when the pressure prevailing in the preform exceeds a predetermined threshold, like this will be explained later.

The preform 1 is for example of the type which is the subject of patent application FR-A-2 668 241 already cited. It is folded back on itself in the longitudinal direction so that in this folded state, which corresponds to that shown in Figure 1, it occupies a footprint very substantially less than the diameter of the well. On the other hand, in its unfolded state, which is visible in particular in Figures 3D and 3E, it has a cylindrical shape with a diameter slightly smaller than that of the well.

As can be seen in FIGS. 4 and 5, the wall of the preform is composed of a core 100 sandwiched between an inner skin 101 and an outer skin 102. The core 100 is made of material composed of filaments impregnated with a thermosetting resin. The skins 101 and 102 are for example thin synthetic fabrics.

At its upper end, the preform 1 is attached to the sleeve 22 by means of a flexible sleeve 10, frustoconical; similarly, its lower end is connected to the jacket 3 by a frustoconical sleeve 11 made of flexible material.

As can be seen in FIG. 4, the sleeve 11 is fixed, for example by gluing, at its lower end to the jacket 3, and by its upper zone to the inner skin 101. As shown in FIG. 5, the sleeve 10 is fixed by its lower zone to the inner skin 101, and in the upper part to the sleeve 22.

The tube 2 passes right through the preform 1 and opens at its lower end into the jacket 3. The latter consists of a body 30, of generally cylindrical shape, the upper end 31 of which is fixed, as already said, to the handle 11, and the lower portion 32 of which carries the shutter 4.

The end of the tube 2 is housed coaxially in a bore provided in the dispensing jacket 3, and is fixed by suitable means not shown. The tube 2 opens into a so-called main pressure chamber 83, the latter opening itself, via an axial channel 830 into a secondary pressure chamber, of cylindrical shape, 8. The inlet of the channel 830 is chamfered, constituting a frustoconical seat 84. The chamber 8, coaxial with the body 30, plays the role of a cylinder for the sliding of a piston 5. The piston 5 has a head against which acts a compression spring 54 which tends to push it back upwards, as well as a tail 500, of smaller diameter, penetrating into an auxiliary chamber 80. The space situated below the piston head which communicates with the outside by a pressure balancing channel 850 .

The chamber 80 communicates, by means of a non-return valve constituted by a ball 89 urged by a spring 890, with a bore 88 which opens into a chamber 81 corresponding to the interior space of the shutter 4. L space 81 communicates through suitable openings 810 with an annular space, against the internal wall of the membrane 40 constituting the shutter 4. This membrane 40 is made of elastically deformable material such as an elastomer. It has the shape of a normally cylindrical sleeve, fixed by its end zones, for example by crimping, to the body 30. When it is subjected to an internal pressure, the obturator inflates radially as shown in FIG. 2 In this same figure, the broken outline of the uninflated membrane has been shown in dashed lines.

The piston 5 is crossed coaxially by a central bore comprising in the upper part a large diameter portion 50 and in part lower portion of smaller diameter 51. In the upper part, the bore 50 opens into the chamber 8 via a chamfered, frustoconical part, 52. The head of the piston 5 is also pierced with a radial bore 53 which communicates bore 50 with the outside. When the piston 5 is in the extreme low position, it bears against an annular stop 35. When it is in the high position, the bore 53 comes in correspondence with a bore 85, also arranged radially, in the body 30 Thus, in this high position, which is shown in FIG. 6B, the bore 50 communicates, via the radial bores 53 and 85, with the outside.

In fact, several radial bores 53 can be provided, regularly distributed angularly, for example three bores arranged at 120 °, and a corresponding number of bores 85 is provided in the body 30.

In the upper part 31 of the jacket 3 is provided a bore 82 which surrounds the tube 2. The latter receives an annular mounting part 6 in which is mounted a thin membrane 60 - called frangible - whose breaking strength is calibrated . Alternatively it could be replaced by a breakaway pin valve.

The frangible membrane 60 delimits a pressure chamber 82 surrounding the tube 2, and which communicates with the channel 830 by a channel 87. At the lower part 32 of the jacket 3 is provided a shutter plug 7, for example cylindrical, housed in a bore of complementary shape. The plug 7 is held in its housing by a breakable pin 70, the breaking strength of which is also calibrated. The bore which is closed by the plug 7 communicates by a channel 320 with the space 81 inside the inflatable shutter 4. The base of the plug 7 is opposite a channel 86 which communicates with the pressure chamber 83 .

At the inlet of channel 86 is mounted a ball valve 860, calibrated to allow a fluid to enter only if its pressure exceeds a certain value, slightly lower than that which causes the pin 70 to break. Thanks to this valve, the fluids can only enter channel 86 at the end of the cycle.

The device is completed by a locking system of the piston 5 in the low position, not shown. This system, which may be of a type known per se, for example with a pivoting ratchet, is arranged in such a way that the piston 5 normally occupies a position close to its extreme low position, preventing the thrust of the spring 54 from raising it. However, this locking system is automatically rendered inoperative following a slight downward pulse given on the piston 5.

Referring now more particularly to FIGS. 3, 3A to 3E and 6, 6A to 6E, we will now explain how the device which has just been described is used for cementing casing from preform 1 in well P.

As shown in FIG. 3, the preform is first lowered into the well by means of the pipe 20, to the desired depth, so that it is opposite the zone Z where it must be fixed.

The shutter 4 is then inflated, as symbolized by the arrows f in FIG. 3A.

The inflation of the shutter is carried out from the surface S by the introduction of a fluid L inside the pipe 20, then the tube 2.

The fluid L is a liquid, for example water or ethylene glycol under pressure, injected into the piping by means of a high pressure circulation pump. As already said above, suitable locking means keep the piston 5 in the low position, almost in abutment against the stop 35.

The pressurized fluid L arrives in the pressure chamber 83, in the channel 830, the auxiliary chamber 8, passes through the piston and arrives in the auxiliary chamber 80. The fluid, due to its pressure, repels the ball 89 from the valve non-return and enters the space 81 inside the shutter, causing it to swell. The membrane 40 therefore comes to be applied intimately against the wall of the well, closing the latter in a sealed manner at the base of the preform. Above a certain pressure, for example 40 bars, the pumping of the fluid L is stopped. Thanks to the non-return valve, the pressurized fluid is retained in the balloon, keeping it inflated.

During the increase in pressure observed during inflation of the balloon, for example between 20 and 30 bars, this resulted on the piston 5 a force directed from top to bottom, which had the effect of making it slide very slightly towards the bottom by releasing its blocking system. The piston thus released, pushed by the spring 54, rises completely when the pumping of the fluid L stops. The configuration of FIG. 6B is then obtained in which the channel 53 has coincided with the opening 85.

Still from the surface, a cement L1 is then sent into the tube 2. This cement is injected at the periphery of the head 3, above the inflated balloon 4, via the opening (or openings) 85 .

The necessary dose of cement has already been determined, the volume of which must correspond substantially to the volume of the annular space between the casing (when the preform will be dilated) and the wall of the well over the entire length of the casing. This volume naturally depends on the length of the casing, the relative diameters between the well and the casing, and surface irregularities of the wall of the tube. It goes without saying, in fact, that if certain wall breaches have a great depth, it is necessary to take them into account when determining the volume of cement to be injected.

The cement L1 is of known nature, capable of ensuring correct fixing of the casing with the wall of the well, for example a hardening resin.

The cement thus injected L1 surrounds the lower portion of the preform 1, over a certain height.

In the same way, another L2 fluid is then injected, called flushing fluid. This is for example a sludge having a density greater than that of cement, and the nature of which is such that it does not easily mix with it. The fluid L2 arrives at the preform base by passing through the openings 85 (see arrows g , FIG. 3B), and comes to occupy the annular space located above the obturator 4 (always inflated). Its volume is calculated in such a way that it drives all of the L1 cement upwards, opposite the preform.

At the end of the injection of the flushing fluid L2, a ball 9 of small diameter is sent from the surface into the piping 20, then passes through the tube 2, at the same time as the fluid L2.

The diameter of the ball, referenced 9 in FIG. 6C is greater than the diameter of the bore 50 but less than that of the bore 830. It therefore crosses the latter, to come to bear against the frustoconical seat 52 forming a chamfer d entry of the channel 50. Since the fluid can no longer penetrate the piston, this results in a push on the latter, which causes it to slide downwards. The piston descends to its lower stop 35, by actuating the trigger of the blocking system, which then automatically locks it in its low position, thus closing the communication with the opening 85. Then, still introduced from the surface, a fluid L3 necessary for the expansion and polymerization of the preform in the pipe 20. The fluid L3 is for example water loaded with solid particles (densifying agent) which give it a density greater than that of the fluids L1 and L2 . It is heated in such a way that it arrives in the jacket 3 at a temperature of the order of 130 ° C., suitable for causing the polymerization of the resin of the preform. It is injected at a pressure of approximately 60 bars, which is sufficient to cause the rupture of the membrane 60. Thus, this liquid is injected inside the preform via the channel 87, the chamber 82 and the space 60 ' occupied by the membrane (see Figure 6C). This achieves progressive inflation of the preform, which expands radially, and from bottom to top because the density of the interior fluid L3 is greater than that of the exterior fluids L2, L1. This progressive expansion, symbolized by the arrows i in FIG. 3C, causes the cement L1 to be pumped up regularly, over the entire length of the preform. The preform assumes, in the unfolded state, a cylindrical shape and constitutes the casing, referenced 1 '; the latter is uniformly coated with cement. It is understood that thanks to this progressive delivery of the cement, it will occupy the entire external surface of the casing, even if, in places, the passage space is small, or even zero.

The heated and pressurized L3 fluid is then circulated inside the preform - which has become casing - this during the time necessary for the polymerization of its wall, generally a few hours. At the same time, the cement sets.

The fluid used for the polymerization is not necessarily the same as that used for the progressive inflation of the preform, because once it has expanded, the density of the interior fluid does not matter. Its function is only to allow the polymerization of the wall.

It should also be noted that it is generally difficult to determine exactly the volume of cement required. In this case, it is prudent to inject a volume of cement slightly higher than the calculated volume, this to avoid that the upper areas of the casing are not properly cemented.

In this case, it is important that the excess cement is destroyed, so that it does not come to make its setting above the casing. This problem can be solved by means of the relief valve 23 provided above the upper end of the preform. At the end of inflation of the preform, the resulting increase in pressure inside the preform and in the tube 2, will cause an escape of the liquid overflow L out of the preform by this valve 23, thus that this is illustrated by the arrows h in Figure 3D. This liquid will remove the excess cement that is at this level. It is thus ensured that the cementing is done only opposite the casing.

At the end of the operation, a second ball is sent to the tube 2, referenced 9 'in FIG. 6D. Its diameter is such that it can pass inside the tube 2, but not inside the bore 830. The ball 9 ′ therefore comes to bear against the chamfered seat 84 at the entrance to this bore 830. The pressure of the fluid L3 is then increased so that it exceeds the setting value of the valve 860. This pressure is transmitted via the channel 86 to the plug 7. It is relatively high, for example of the order of 100 bars, sufficient to cause breakage of the pin 70. The plug 7 is therefore driven out, as illustrated in FIG. 6E, so that the liquid which was trapped in the shutter 4 can freely escape towards the bottom of the well through the channel 320. The shutter deflates, as symbolized by the arrows j in FIG. 3E, while the fluid L2 which was above the shutter also falls to the bottom of the well.

The device should then be removed from the well. For this, pull upwards on the pipe 20, as symbolized by the arrow K in FIGS. 3E, 4 and 5.

As a result of this traction, the sleeve 10 detaches from the inner skin 101 of the casing (see FIG. 5).

In the lower part, the sleeve 11 turns over, and causes the removal of the inner skin 101, also by turning over in the manner of a sock (see FIG. 4A where this turning over is symbolized by the arrows r ).

The inner skin 101 is thus gradually and completely torn off as the device is removed.

At the end of the operation, the cemented casing remains, stripped of its inner skin.

Of course, the cycle which has just been described can be repeated in order to cement end to end a set of casings.

The diagram in FIG. 7 schematically illustrates the value of the pressures applied during the process.

The rectilinear curve portion OA represents the initial pressure increase during inflation of the hydraulic shutter, up to a pressure P 0, for example equal to approximately 30 bars.

The section of the curve AB corresponds to the end of inflation of the shutter at the pressure P1 (approximately 35 bars); during this phase the pressure exerted on the piston head causes it to move downwards, thereby releasing its locking mechanism. The section of curve BC corresponds to the stopping of the injection and to the upward movement of the piston (pushed by the spring 54) gradually discovering the openings 85.

The fluid injected so far is L.

The CD phase corresponds to successive injections of L1 cement and L2 flushing fluid.

The point E corresponds to the sudden rise in pressure when the ball 9 pumped at its seat 52 is pumped at the end of the flushing fluid in order to obstruct the internal channel 50/51 of the piston.

The part of the curve EF corresponds to the stopping of pumping, the pressure remaining constant. Phase FG represents the rise to the pressure P4 of rupture of the device making it possible to open the circulation inside the preform. As an indication, P4 = 60 bars.

The GH phase corresponds to the sudden drop in pressure resulting from the opening of the circulation inside the preform.

Phase HI corresponds to the inflation of the preform by means of the fluid L3 (pressure P5). At the end of inflation, the pressure increases, which corresponds to the segment IJ , until reaching the pressure controlled by the valve 23. The phase JK corresponds to the polymerization of the preform. The pressure P6 prevailing in the preform is substantially constant, because it is controlled by the valve 23. As an indication, we have P6 = 20 bars. Point L corresponds to the positioning of the ball 9 '. The part of the curve LM corresponds to the stopping of pumping, the pressure (P7) remaining constant. Then, the pumping is resumed, and this results in a very significant increase in the pressure corresponding to the segment MN. The pressure P8, for example of the order of 100 bars is sufficient to achieve the rupture of the pin 70, causing the instantaneous deflation of the hydraulic shutter, which corresponds to the rapid drop in pressure of the segment NQ .

Claims (11)

1. A method of cementing casing inside a borehole or a conduit that is approximately cylindrical, using a tubular preform that is deformable by being expanded radially from a "folded" first state in which its maximum transverse dimension is considerably smaller than the diameter of the well or conduit, to an "unfolded" second state in which it is cylindrical in shape and has a diameter that is slightly smaller than that of the well or the conduit, the preform being settable on site in order to constitute the casing, the method being characterized by the fact that it comprises the following steps:

   a) the preform (1) in the folded state is inserted into the well or into the conduit (P), and it is lowered down to the desired level;

   b) the well or the conduit (P) is closed at the bottom of the preform (1) by inflating in said zone a hydraulically deformable closure member (4);

   c) a cement (L1) that is fluid and settable is injected above the closure member (4) so as to surround the bottom portion of the preform, with the volume of said cement (L1) corresponding substantially to the volume required for cementing the casing in the well or in the conduit;

   d) the preform (1) is deformed to cause it to take up its unfolded state, said deformation taking place progressively from the bottom upwards, so that the cement is displaced little by little along the annular space between the preform (1) and the wall of the well or of the conduit, along the entire height of the preform;

   e) the preform (1) is caused to set so as to obtain the casing (1'), and the cement (L1) is allowed to set; and

   f) the closure member (4) is deflated and withdrawn from the well or the conduit.
2. A method according to claim 1, characterized by the fact that said closure member (4) is inflated from the surface by means of a hydraulic fluid which is delivered by a tube (2) that passes longitudinally right through the preform (1).
3. A method according to claim 2, characterized by the fact that after the cement (L1) has been injected in step c), a non-setting other fluid (L2) - a "flush fluid" - of density greater than that of the cement (L1) is injected so as to occupy the space extending between the closure member (4) and the bottom end of the preform (1).
4. A method according to claim 2 or 3, characterized in that the cement (L1) and optionally the flush fluid (L2) are delivered from the surface via the same tube (2) as is used for inflating the closure member (4), passing via a distributor jacket (3) mounted at the end of the tube (2) which carries said closure member (4).
5. A method according to claim 4, implemented using a preform (1) having a wall that sets by polymerizing when heat is applied thereto, the method being characterized by the fact that the preform is caused to expand radially and to set by means of a hot fluid which is delivered from the surface via said tube (2), and via said distributor jacket (3).
6. A method according to any one of claims 1 to 5, characterized by the fact that after step d) a fluid (L3) is injected into the zone situated above the top end of the preform (1) to eliminate any excess cement that may be present in said zone.
7. The use of a cementing device in a method according to claims 1 to 6, the device being characterized by the fact that it comprises a fluid feed tube (2) passing right through the preform (1) and having its bottom end connected to an inflatable hydraulic closure member (4).
8. A use according to claim 7, characterized by the fact that it is provided with a fluid distributor jacket (3) into which the bottom end of said tube (2) opens out.
9. A use according to claim 8, characterized by the fact that said distributor jacket (3) constitutes a multi-port valve enabling the fluid feed tube to be caused to communicate selectively with the inside of the closure member (4), with the outside, and with the inside of the preform (1).
10. A use according to claim 9, characterized by the fact that said distributor jacket (3) possesses pressure chambers (8, 83) having outlets closable by balls (9, 9') that are put into place, in operation, via the fluid feed tube (2).
11. A use according to any one of claims 7 to 9, characterized by the fact that the fluid feed tube is provided with a valve (23) situated above the top end of the preform.

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