Abstract:
Introducing within a well or pipe a mandrel equipped with an inflatable membrane which can expand radially under the effect of an internal pressure. Positioning the mandrel opposite the portion to be treated, in introducing a pressurized fluid within the membrane such that its end regions form annular bulges pressing firmly against the wall, whereas its mid-region expands to a lesser degree. Forming a peripheral annular space into which is then injected a cement which is liquid but able to harden. Leaving the cement to set so as to form a solid sleeve. Deflating the tubular membrane. Withdrawing the mandrel together with the deflated membrane. The method can be used in the oil sector, particularly for repairing and/or plugging a portion of casing.

Description:
BACKGROUND OF INVENTION 
     The present invention relates to a method and a device for cementing a well or a pipe, for example a casing, having a portion to be treated so as to make it leaktight, in particular to be repaired and/or plugged. 
     It applies more particularly, but not necessarily, to the field of oil production. 
     The casing is a metal tube which lines the interior of the oil well over a considerable length. 
     As an indication, this length is for example between 2000 and 4500 meters, whereas its internal diameter is between 120 and 200 millimeters. 
     In the lower part, the casing is perforated at the level of the deposit(s) that it passes through, so as to allow the passage of oil or a gaseous hydrocarbon. 
     Located in the upper part of the well is the wellhead, which is equipped with various systems, in particular for protection, suspension and sealing purposes. 
     Over a considerable length of the upper part of the well, for example between 1500 and 4000 meters, the casing is provided internally with completion equipment comprising a tube and various devices serving for exploitation of the well, such as temporary plugs and safety valves for example. 
     Over time, a portion of the wall of the casing may have to be sealed, in particular if has deteriorated, for example due to premature wear and/or cracking, or when the perforations intended for the passage of oil have to be plugged, in particular because the deposit has been depleted in this zone and undesirable fluid products (in particular water or gas) risk passing through the wall of the casing and penetrating into the latter. 
     For this purpose, said portion is treated by coating it internally with a protective material, in particular a cement, a gel or a composite material based on polymerisable resin. 
     In order to carry out this treatment, two different techniques may be used:
         either the completion equipment is removed beforehand and it is then possible to gain direct access to the portion of the casing to be treated,   or the tools and the material used for cementing purposes are passed through the completion equipment.       

     The first technique is time-consuming and expensive and may cause exploitation problems, in particular due to the fact that it is necessary to completely neutralise the well prior to any intervention. 
     The second technique is complicated, expensive and can be used only in a certain limited number of configurations, due to the fact that the completion equipment generally has a much smaller diameter than that of the lower zone of the casing in which the portion to be treated is located. 
     In particular, the installation of a cement coating is generally not possible using this technique. 
     The invention aims to overcome these difficulties by proposing a method and a device which make it possible to cement the lower zone of the casing while passing through the completion equipment of smaller diameter. 
     The invention can be applied not only to a casing as described above, but also to any hollow well in the ground or to any pipe, buried or otherwise, and for this reason the description and the claims which will follow refer to the cementing of a well or a pipe, the latter being able to be a casing or any other conduit, vertical, horizontal or oblique. 
     SUMMARY OF THE INVENTION 
     The subject matter of the invention is therefore a method for cementing a well or a pipe, for example a casing, having a portion to be treated, in particular to be repaired and/or plugged. 
     According to this method: 
     a) a tubular mandrel is introduced into the well or pipe, around which mandrel there is mounted an inflatable membrane which is also tubular and is made of a flexible and elastic material which can expand radially under the effect of an internal pressure, and this assembly is positioned opposite the portion to be cemented; 
     b) a pressurised fluid is introduced into the membrane and the latter is inflated in such a way that, on the one hand, its end zones dilate radially and considerably, forming annular beads which are applied firmly against the wall of the well or pipe, on either side of the portion to be cemented, and that, on the other hand, its zone—referred to as the median zone—located between its end zones also dilates radially, but with a lesser amplitude, so that an annular space is formed between this median zone and the portion of wall to be cemented; 
     c) while the membrane is kept inflated, a liquid but curable cement is injected into this annular space; 
     d) the cement is left to set so that it forms a solid sleeve which internally coats said wall portion of the well or pipe; 
     e) the tubular membrane is deflated; 
     f) the assembly consisting of the mandrel and the deflated membrane is withdrawn from the well or pipe. 
     The device for cementing a well or a pipe, for example a casing, having a portion to be treated, in particular to be repaired and/or plugged, which device also forms the subject matter of the invention, is characterised in that it comprises an assembly which is designed to be introduced into the well or pipe and to be positioned opposite the portion to be cemented, this assembly consisting of a tubular mandrel and an inflatable membrane which is also tubular and surrounds said mandrel, the wall of the membrane being made of a flexible and elastic material which can expand radially under the effect of an internal pressure, means being provided for introducing a pressurised fluid into said membrane in order to inflate it, and in that the end zones of said membrane are able to dilate radially and considerably in such a way as to form annular beads which can be applied firmly against the wall of the well or pipe, on either side of the portion to be cemented, and that, on the other hand, its zone—referred to as the median zone—located between its end zones also dilates radially, but with a lesser amplitude, so that an annular space is formed between this median zone and the portion of wall to be cemented, this device additionally comprising means for injecting a liquid but curable cement into this annular space while the membrane is kept inflated, and means for deflating said membrane once the cement has set. 
     Furthermore, according to a certain number of advantageous, but non-limiting, features of this device:
         said tubular membrane is secured to said mandrel by an annular part—referred to as the anchoring part—which is radially non-extendable and is located within said median zone, whereas its end zones are fixed to movable rings which are guided in translation in a sealed manner on the mandrel and can slide axially on the latter as a result of the inflation or deflation of said membrane;   the median zone of said membrane is provided with means capable of limiting its radial expansion to a predetermined maximum diameter;   said membrane is reinforced by an armature comprising at least one ply of cables, wires or fibres wound helically with respect to its longitudinal central axis;   in said median zone, the initial angle formed tangentially by said cables, wires or fibres with respect to the longitudinal central axis of the membrane is such that, after inflation, the diameter of the membrane reaches a predetermined given value when this angle reaches a value of around 54°;   the transition between the anchoring part of the membrane and the portions of its median zone with limited radial expansion takes place by means of portions, referred to as “portions adjacent to the anchoring part”, which are able to deform under the effect of the inflation so as to be placed in planes which are substantially perpendicular to the longitudinal central axis of the membrane;   the initial angles of inclination (before inflation of the membrane) of the cables, wires or fibres with respect to the longitudinal central axis of the membrane have approximately the following values:   of around 18° to 25° in the end zones of the membrane;   of around 35° to 45° in its median zone, except in the portions adjacent to the anchoring part;   of 0° in the portions adjacent to the anchoring part;   said membrane is reinforced by an armature comprising several plies of wires or fibres wound helically with respect to its longitudinal central axis, the directions of winding of the two superposed plies being reversed;   the portions adjacent to the anchoring part are grooved, each of these portions having at least one groove located in the axial extension of a similar groove formed in the other portion, so that, after inflation of the membrane, they form a channel for injection of the cement, this injection taking place through at least supply orifices penetrating the tubular mandrel and the anchoring part, via a suitable valve;   the wall of the mandrel is penetrated by inlet orifices for an inflation fluid, which orifices open into the interior of the membrane between said movable rings and said anchoring part;   the wall of the membrane is grooved externally at its end zones, so as to allow the evacuation of the fluid present in the well or pipe during inflation;   said membrane is covered with a thin-walled sleeve which is made of a flexible and elastic material and which can be pressed against the portion of wall to be cemented when the cement is injected into the annular space formed between the median zone of the membrane and the portion of wall to be cemented;   said sleeve is able to inflate, increasing in volume in the direction of its thickness, when it is in contact with the liquid present in the well or pipe, so as to ensure good sealing with the zone of the well to be sealed;   the device comprises means so that one of the two annular end beads is applied against the wall of the well or pipe before the other end bead.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features and advantages of the invention will become apparent from the description which will now be given thereof, with reference to the appended drawings, in which: 
         FIGS. 1 and 2  show, in a highly schematic manner and in axial section, part of an oil well respectively before and after cementing of a damaged portion. 
         FIGS. 3 and 4  are schematic views of a device according to the invention, in the non-inflated state, respectively in axial section and in front view. 
         FIGS. 5A and 5B  show the same device after inflation,  FIG. 5A  being an axial half-section and  FIG. 5B  being a front half-view. 
         FIGS. 6A and 6B  are diagrams of the same device which are intended to show the orientations of the wires or fibres of the armature of the membrane, before ( FIG. 6A ) and after ( FIG. 6B ) the inflation. 
         FIG. 7  is a cross section of the device in the plane VII-VII of  FIGS. 5A and 5B . 
         FIGS. 8A and 8B  are diagrams which show the change in orientation of the wires or fibres of two adjacent plies as a result of the inflation. 
         FIGS. 9 to 14  illustrate various steps of the method. In these figures, the longitudinal axis of the well or pipe (and therefore of the device) has been shown horizontally in order to facilitate the page layout of the drawings; this axis could of course be vertical, as in  FIGS. 1 and 2 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows part of an oil drilling well, lined with a casing C with a cylindrical wall and of vertical axis X-X′. A portion Z of this casing has for example perforations p, producing water, which it is desired to plug by means of cementing. 
     Reference EC denotes completion equipment, held in place by an annular centring element A, and the internal diameter d of which is much smaller than the diameter D 0  of the casing. 
     By way of example, the diameter d is around 69 mm whereas the diameter D 0  is around 155 mm. 
       FIG. 2  shows the same well part after installing a cement coating GC in the portion Z. 
     In order not to disrupt exploitation of the well, it is important that the internal diameter D of this coating is greater than d. 
     It will be understood that this installation usually poses difficulties when it takes place through the completion equipment EC. 
     As will now be explained, the invention nevertheless makes it possible to carry out this procedure easily. 
     The device of the invention which is shown in  FIGS. 3 to 7  essentially comprises a cylindrical tubular mandrel  1 , of axis X-X′, for example made of steel, which is covered with a similarly cylindrical membrane  2 , in the form of a sleeve, made of a flexible and elastic material which is resistant to pressure and corrosion, for example rubber or elastomer. 
     At rest ( FIGS. 3 and 4 ), the membrane surrounds the mandrel without play, or even with a slight clamping action. 
     The mandrel has a closed free end  100 . 
     Only the end portion of the mandrel carrying the membrane is shown. This mandrel is mounted at the end of a rod of considerable length (located towards the right in  FIGS. 3 and 4 ), which passes into the tube of the completion equipment EC, and meets the wellhead. 
     The overall diameter of the assembly consisting of the mandrel and the membrane is slightly smaller than the internal diameter d of the completion equipment EC, so that it can pass through the latter in the axial direction. 
     Its length is selected as a function of that of the zone Z to be treated; it is a few meters for example. 
     In its end zones  20   a ,  20   b , the membrane  2  is fixed, for example by glueing, to rings  4   a  and respectively  4   b  which are guided in axial translation on the mandrel  1 . 
     Between the end zones  20   a ,  20   b , and markedly closer to the zone  20   b  than to the zone  20   a  in the embodiment shown, a zone  21  of the membrane is directly fixed around the mandrel by a thin annular part of small length, referred to as the anchoring part. This fixing is carried out for example by means of a small clamping ring which is embedded in the membrane (and is not shown), supplemented by glueing. 
     The zone  21  is grooved longitudinally; in the example shown, four identical grooves  6  are provided which are spaced apart by 90° with respect to the axis X-X′ and have a semi-circular cross section. 
     Their centre is located at the aforementioned anchoring part, from which “half-grooves”, referenced  6   a  and  6   b , therefore depart. 
     At the anchoring part, the mandrel is pierced by four radial orifices  10  which each open, via corresponding perforations  60  provided in the wall of the membrane, into the centre of a groove  6 . 
     Over a certain length, denoted Pa, Pb in  FIG. 4 , of each connection zone  20   a  and respectively  20   b  of the membrane with the rings  4   a  and  4   b , the tubular membrane is able, as will be seen below, to dilate radially with a relatively great amplitude, under the effect of an internal pressure. 
     On one side (on the right of the figure), this part—which will be referred to overall as the “end zone”—connects the zone  20   b  to the zone  21 , the length of which is referenced R. 
     On the other side, an intermediate part—referred to as the “median zone”—is placed between the zone  20   a  and the zone  21 . 
     This median zone has a length Q which is substantially equal to, or slightly greater than, that of the portion to be cemented. 
     The end zones are provided with peripheral grooves  22   a ,  22   b.    
     On each side of the anchoring part of the membrane, the mandrel  1  is pierced by a certain number of orifices  11   a  and  11   b  which are similar to the aforementioned orifices  10 . 
     The opening and closing of the orifices  10  and  11   a ,  11   b  is controlled by suitable valves W and respectively Va, Vb. 
     The membrane  2  is partially covered by a sleeve  5  made of a flexible and thin material, for example rubber, which connects the end zones and terminates more or less in the middle of the grooves  22   a  and  22   b  (see  FIG. 3 ). This sleeve is assumed to have been removed in  FIGS. 4 to 6  so as not to be detrimental to the legibility thereof. 
     The wall of the membrane  2  is reinforced by an inner armature  3 , embedded within its wall. 
     As known per se (see for example the document U.S. Pat. No. 5,695,008), this armature consists of several concentric plies (or layers) consisting of flexible wires or fibres with high mechanical strength, wound in a helical manner. 
     The directions of winding of two superposed plies are reversed so that the membrane deforms in a homogeneous manner, in particular without any twisting. 
     During the radial expansion of the membrane, the angle of inclination of the tangent to each fibre with respect to the longitudinal axis X-X′ gradually increases and may—as is also well known—reach an equilibrium value of 54°, beyond which expansion is no longer possible. 
     According to one feature of the invention, the angle of winding of the fibres or wires is not the same over the entire length of the membrane, as illustrated in  FIG. 6 . 
     In the end zones of length Pa and Pb, the wires or fibres are referenced  90   a , respectively  90   b  before inflation and  90 ′ a , respectively  90 ′ b  after inflation. They form, with respect to the axis X-X′, an initial angle, referenced respectively α 0  and γ 0 , with a relatively low value. This value is determined taking account of the initial diameter of the membrane and the internal diameter of the wall of the casing, against which these zones have to bear after inflation. 
     It is therefore necessary for the angle α and respectively γ after inflation to be less than the limit angle of 54°. 
     In the intermediate median zone of length Q, in which the wires or fibres are referenced  91  before inflation and  91 ′ after inflation, the angle β 0  must have a value larger than the angles α 0  and γ 0 . 
     Its value is determined taking account of the initial diameter of the membrane and the internal diameter which the sheath of the cement coating must have after the operation. 
     This is because the radial expansion of this median zone must be limited upon inflation, and the angle of 54° must be reached before this zone bears against the wall of the casing, after a given amplitude of expansion, which will calibrate the peripheral space which is intended to receive the cement. 
     In practice, the value of the angles α 0  and γ 0  is for example around 18 to 25° and that of the angle β 0  is around 35 to 45°. 
     After inflation, the angles α and γ have a value of around 45° and the angle β is close to 54°. 
     In the grooved zone  21  of length R which extends on either side of the anchoring part, the fibres or wires of the armature, referenced  91   a  and  91   b , are directed in the axial direction, thus forming a zero angle with respect to the axis X-X′. By virtue of this arrangement, the deformation upon inflation of this portion adjacent to the anchoring part is not hindered by the presence of the fibre or wire armature, even though the zones of the membrane located on either side of the anchoring part are placed in planes perpendicular to the axis X-X′ as a result of the inflation, moving closer to one another, as can be seen in  FIGS. 5A ,  5 B,  6 A, and  6 B. 
     The half-grooves  6   a  and  6   b  are thus arranged opposite one another, forming a radial channel  6 . 
     The orifices  10  are connected by means of a suitable conduit  80  to a source  8  for distributing a liquid but curable material L 2 , such as a cement loaded with short fibres, it being possible for this distribution to take place via a pump located in the wellhead or directly in the well from a suitable reservoir. 
     Similarly, the orifices  11   a  and  11   b  are connected by means of a suitable conduit  70  to a source  7  for distributing, at high pressure, a fluid L 1 , for example water, it also being possible for this distribution to take place via a pump located in the wellhead or directly in the well by using the fluid present therein. The orifices  11   a  and  11   b  are also connected to a source for aspirating  7 ′ the fluid L 1 , thus making it possible to deflate the membrane at the end of the operation. 
     Referring to  FIGS. 9 to 14 , it will now be explained how the device that has just been described is used to cement a casing, according to the method of the invention. 
     With reference to  FIG. 9 , the device is moved in the deflated state until it is opposite the portion Z of the casing C that is to be treated. 
     The membrane  2  is then inflated, after having brought about the opening of the valves Va and Vb (the valve W being closed), by introducing the pressurised fluid L 1  between said membrane and the outer wall of the mandrel  1  via the orifices  11   a  and  11   b , as symbolised by the arrows f 1  in  FIG. 10 . During the inflation, the end rings slide axially and move towards one another (arrows d 1 ) since the radial expansion of the membrane causes it to shorten in the axial direction. 
     Suitable retaining means, not shown, are advantageously provided so that one of the zones forming a bead, for example Pb, inflates fully before the other zone (for example Pa) so as to prevent any jamming of the device in the longitudinal direction during the inflation. 
     These means are for example frangible wires which are wound around these zones and can be broken at a given pressure, those surrounding the zone Pb being designed to break before those surrounding the zone Pa. 
     Another solution, for example, is to offset slightly over time the supply to the interior spaces in these zones, thus offsetting the opening of the valve Va with respect to that of the valve Vb. 
     The end zones form beads which are pressed firmly against the wall of the casing. On the other hand, since the median zone has a limited expansion due to the greater inclination of the wires or fibres of the armature, a peripheral annular space Σ remains at this location. 
     With reference to the diagram in  FIG. 8A , it is possible to see, before inflation, two “crossed” series of fibres or wires  9 . 1  and respectively  9 . 2  belonging to two adjacent (superposed) plies of the armature  3  with which the median zone is provided. 
     At the end of inflation, shown in  FIG. 8B , this armature—denoted  3 ′—has been deformed, the fibres or wires  9 . 1 ′ and  9 . 2 ′ of each of the two plies having a modified inclination, so as to form an angle of around 54° with respect to X-X′. 
     The two portions adjacent to the anchoring part, for their part, are placed in transverse planes and are pressed against one another. 
     Of course, the connections between the different zones take place in a gradual manner, due to the flexibility and elasticity of the membrane and also a gradual change in the angles of the fibres, and not via sharp angles. 
     Once the membrane has inflated, the valves Va and Vb are closed in order to keep the membrane in this state. 
     It then forms a type of counter-mould, or coffer, for moulding the cement. 
     The valves W are then opened and the liquid cement L 2  is introduced, via the orifices  10  and the channels  6  in the peripheral space Z, into the sleeve  5 . The latter is then inflated in turn, chasing away the liquid present in the well, for example sludge, which is located in the space Z. This liquid can escape via the grooves  22   a ,  22   b  provided for this purpose in the end zones of the wall, which form beads. 
     This escape is symbolised by the arrows e in  FIG. 11 . 
     Thus, as shown in  FIG. 12 , the liquid cement L 2  finally fills the entire space Z, with the sleeve  5  being pressed against the casing. 
     The valves W are then closed and the cement is left to set. 
     Once it has sufficiently hardened, the membrane is deflated by aspirating the inflation fluid L 1  (arrows f 2 ); the membrane retracts radially and extends axially (arrows d 2 ). It returns to its initial configuration. 
     The cement forms an annular jacket GC which coats the zone Z and makes it leaktight by virtue of the presence of the sleeve  5 . 
     The cement injection cores s which correspond to the channels  6  and which still adhere to this sheath can be cut off either simply as the device is withdrawn or by means of a special tool (arrows J,  FIG. 14 ). 
     The same device can optionally be reused to treat other portions of the casing, or even other casings. 
     In this case, the cementing is carried out without the sleeve  5 . 
     By way of indication, the thickness of the wall of the jacket GC is for example between 35 and 40 millimeters, whereas its internal diameter is around 80 mm. Its length may be several meters. 
     In the present description, the term “wires or fibres” will also be understood to mean similar filiform elements such as cables or cords. 
     These elements may be made of any material with high mechanical strength, for example steel, carbon or aramid. 
     Means other than those described above could of course be used to limit the amplitude of radial expansion of the median zone of the preform. For example, it could be provided with a flexible and non-extendable armature which is initially slack and can deform radially at the same time as the membrane over a limited course, beyond which it is taut.