The invention relates to isolation of part of a well, which comprises pipe provided, along its external face, with a first external sleeve, wherein the opposite ends are connected directly or indirectly to said external face of the pipe. The pipe, first external sleeve and its ends together delimit an annular space, the wall of said pipe exhibiting at least one opening which allows it to communicate with said space, this sleeve being likely to expand and to be applied tightly against the well over an intermediate part of its length. The device also comprises on the one hand, a second internal sleeve, which extends between said pipe and the first sleeve, its ends being also connected directly or indirectly to the external face of said pipe and, on the other hand, at least one communication passage between the exterior of the first sleeve and said space.

[0001]    The present invention relates to the field of well drilling. 
         [0002]    It relates more particularly to an isolation device of part of a wellbore. 
         [0003]    This invention applies especially but not exclusively to the casing of a horizontal well. This casing is called “pipe” in the remainder of the document. 
         [0004]    This well configuration has become widespread over recent years due to novel extraction techniques. 
       BACKGROUND OF THE INVENTION 
       [0005]    A horizontal well, inter alia, considerably increases the productive length and therefore the contact surface with the geological formation in which gas and/or oil is present in source rock. 
         [0006]    In such a horizontal configuration, it is technically difficult to case and cement the annular space between the pipe and the inner wall of the well in a horizontal position. This cementing technique, used in the majority of vertical or slightly deviated wells, provides a seal between different geological zones. 
         [0007]    The exploitation of horizontal wells, whether for stimulation or flow control, requires some zones to be isolated in the rock formation itself. 
         [0008]    A pipe is run into the well with isolation devices at its periphery, spaced out in predetermined fashion. 
         [0009]    The term “zonal isolation packers” is used for these devices. Between these isolation devices the pipe often has ports open or closed on demand, which enable communication between the pipe and the isolated zone of the well. 
         [0010]    In this horizontal completion environment, hydraulic fracturing (also called “fracking”) is a technique for cracking of the rock in which the pipe is set horizontally. 
         [0011]    Cracking is carried out by injection of a liquid under pressure. This technique enables extraction of oil or gas contained in highly compact and impermeable rocks. 
         [0012]    The injected liquid generally comprises 99% water mixed especially with sand or ceramic microballs. The rock fractures under the effect of pressure and solid elements penetrate inside fissures and keep them open when the pressure drops so that gas or oil can flow through the resulting breaches. 
         [0013]    These days fracking is mostly carried out by using an assembly of pipes such as described above. The zones are fractured one by one so that the quantity of fluid injected can be controlled. The fluid is indeed injected in limited volumes that are spread along the well. Pressures up to 1000 bar (15 000 psi) can be reached. 
         [0014]    A key element of these fracking completions is located in the isolation and sealing device. It has to ensure perfect sealing between the zones to guarantee the quality and safety of fracking. 
         [0015]    Indeed, if sealing not ensured, a zone could be fractured several times, creating an excessively large fracture and reaching unplanned geological zones. 
         [0016]    During these fracking operations, isolation devices are subjected to high internal, external and differential pressures. Also, the injected fluids often have a lower temperature than that of the well, subjecting isolation devices to variations in temperature. 
         [0017]    Several types of isolation devices are currently being used. 
         [0018]    Hydraulic-set isolation devices “Hydraulic Packers” which utilise hydraulic pressure to compress a rubber ring via one or more pistons are being used. 
         [0019]    This rubber ring expands radially and comes into contact with the borehole. 
         [0020]    The patent U.S. Pat. No. 7,571,765 is a typical example of this type of hydraulic-set isolation device. 
         [0021]    It is clear that when used this type of device does not properly seal a well having an ovalised cross-section. 
         [0022]    Also, a fracture of the rock can be initiated at the packer level due to high contact pressure. Hydraulic isolation devices are also sensitive to temperature variations. 
         [0023]    Other types of devices can be used. 
         [0024]    In this way, mechanical isolation devices “mechanical packers” have a working principle close to that of hydraulic isolation devices, the only difference is that the compression of the rubber ring is carried out by an external tool. 
         [0025]    Also, inflatable isolation devices (in English “inflatable packers”) comprise an elastic membrane inflated by injection of liquid under pressure. After activation, the pressure is maintained in the sealing device by check valve systems. 
         [0026]    Isolation devices based on swellable elastomer (in English “swellable packers”) are composed of an elastomer which swells when placed in contact with a type of fluid (oil, water, etc.) according to formulations. 
         [0027]    Activation of these devices is initiated by contact with fluid. It is therefore understood that diameter increase must be relatively slow so as to avoid blockage of the completion during the run in hole. As a consequence, it sometimes takes several weeks to achieve the isolation of the zone. 
         [0028]    Other types of isolation devices are those known as “expandable” (in English “expandable packers” or “metal packers”) and comprise an expandable metallic sleeve which is deformed by application of liquid under pressure (see the article SPE 22 858 “Analytical and Experimental Evaluation of Expanded Metal Packers For Well Completion Services (D. S. Dreesen et al—1991), U.S. Pat. No. 6,640,893 and U.S. Pat. No. 7,306,033). 
         [0029]    Expandable isolation devices made of metal usually comprise a ductile metallic sleeve attached and sealed at its ends to the surface of a pipe. The interior of the pipe, on the one hand, and the ring defined by the external surface of the pipe and the inner surface of the expandable sleeve, on the other hand, communicate with each other. The metallic sleeve is expanded radially towards the exterior until it makes contact with the borehole, by increasing the pressure in the pipe to create an annular barrier. 
         [0030]    Contrary to other isolation devices, sealing is not based on elastomer means only, whereof the efficiency over time and under severe conditions is uncertain. Also, fracking often makes use of fluids at external ambient temperature whereas isolation devices are brought to the temperature of the well. 
         [0031]    Expandable metal sleeves are less sensitive to temperature variations and more particularly to thermal contraction. The value of the coefficient of thermal expansion of the metal is lower than that of elastomer. 
         [0032]    These expandable metal isolation devices therefore combine the advantages of devices explained earlier. First, as isolation devices based on inflatable elastomer, their design is simple and inexpensive and also they can be activated on demand as hydraulic isolation devices, soon after the completion has been run in the well. 
         [0033]    Purely by way of illustration  FIG. 1  illustrates a portion of pipe capable of being run in a well. This portion of pipe illustrated here is provided with two isolation devices  2  between which extends a portion of pipe  1  which presents a set of through openings  3 . 
         [0034]    This pipe  1  is illustrated again in the bottom part of the figure, the isolation devices  2  set in an expanded position. 
         [0035]    The arrow v represents the circulation of fluid inside the pipe for fracking, that is, from upstream to downstream. 
         [0036]      FIG. 2  is a simplified sectional view of the pipe such as that in  FIG. 1 , which extends into a previously prepared well. 
         [0037]    The aim of the description of this figure is simply to explain how pipes provided with such zonal isolation devices has been used to date. 
         [0038]    A well A whereof the wall is referenced A 1  has previously been drilled in the ground S. 
         [0039]    Pipe  1  which is illustrated partially here has been set in place inside this well. 
         [0040]    Along its wall, this pipe has, at regular intervals, isolation devices  2 . In this case, just two devices  2  designated N and N−1 are illustrated by way of simplification. 
         [0041]    In practice, there is a larger and substantial number of such devices along the pipe. As is known, each device is constituted by a tubular metallic sleeve  20  whereof the opposite ends are connected directly or indirectly to the external face of the pipe by reinforcing rings or skirts  21 . 
         [0042]    Pressure P 0  prevails in the well. 
         [0043]    Initially, the metallic sleeves  20 , not deformed, extend substantially in the extension of the rings  21 . 
         [0044]    The distal end of the pipe preferably comprises a port, not illustrated here, which is initially open during the descent of the pipe into the well so as to allow circulation of fluid from upstream to downstream at pressure P 0 . This port is preferably closed by means of a ball which is placed in and blocks this port, increasing the pressure in the pipe is then possible. 
         [0045]    A first fluid under pressure P 1  greater than P 0  is then sent inside the pipe. The fluid circulates through openings  10  arranged in front of the sleeves  20  along the entire pipe so as to expand the metallic sleeves and take the position of  FIG. 2  in which their intermediate central part is in contact with the wall A 1  of the well. 
         [0046]    Of course, the material of the sleeve and the pressure are selected so that the metal deforms beyond its elastic limit. 
         [0047]    A device, not illustrated, frees up an opening located at the distal end of the pipe when the pressure P 1  is slightly raised. The pressure at the level of the opening goes from P 1  to P 0  and circulation is then possible in the pipe from upstream to downstream of the well. 
         [0048]    Next, another ball  5  is launched inside the pipe and lands in a sliding seat  4  located substantially mid-distance between the two isolation devices N and N−1. 
         [0049]    Originally, the seat  4  is located just opposite the abovementioned openings  3  and seals them. Under the effect of displacement of the ball, the seat  4  is closed and shifts, freeing up the openings  3 . A fracking fluid under very high pressure is then injected inside the pipe  1 . 
         [0050]    This fluid, under pressure P 2 , is introduced in the device N as well as in the annular space B which separates the devices N and N−1. 
         [0051]    However, the prevailing pressure inside the device N−1 returns to the initial pressure of the well, that is, to the pressure P 0 . 
         [0052]    In these conditions, the difference in pressure which exists between the annular space B and the device N−1 exposes the sleeve  2  of the device N to high stresses which in some places leads it to partially collapse. It is understood that this constitutes a source of leaks, meaning that the zone B to be fracked is no longer fluid or gas tight. 
         [0053]    Systems have been added to this kind of devices to withstand collapse. An example is given in document WO 2011/042 492. Another option is to use this pressure difference by way of valves to maintain internal pressure in the device after expansion or to “capture” this pressure difference (see U.S. Pat. No. 7,591,321, US 2006/004 801 and US 2011/02 66 004). Yet, all these solutions mean greater complexity of the materiel and risk of malfunctioning. 
         [0054]    From EP-A-1 624 152 is known a device in which each sleeve of the pipe is equipped with a “skin” which extends only along a part of said sleeve. Between the sleeve and the skin is present a sealant material. 
       BRIEF SUMMARY OF THE INVENTION 
       [0055]    The aim of the present invention is to cope with these difficulties. 
         [0056]    More specifically, it relates to an isolation device of part of the well which is capable of resisting high differential pressures while having considerable sealing capacity. 
         [0057]    Also, the system according to the invention has expansion pressure less than the fracking pressure and is not sensitive to changes in temperature. 
         [0058]    As a result, this isolation device of part of a well which comprises a pipe provided along its external face with at least one metallic tubular sleeve—called “first external sleeve”—whereof the opposite ends are connected directly or indirectly to said external face of the pipe. This pipe, the first external sleeve and its ends together delimiting an annular space, the wall of said pipe exhibiting at least one opening which allows it to communicate with said space, this sleeve being likely to expand and to be applied tightly against the wellbore over an intermediate part of its length is 
         [0059]    characterised in that it comprises:
       on the one hand, a second sleeve also expandable—called “second internal sleeve”—which extends between said pipe and the first sleeve, its ends being also connected directly or indirectly to the external face of said pipe, while being sandwiched between the ends of the first sleeve and the external face of the pipe,   on the other hand, at least one communication passage between the exterior of the first sleeve and said space,   said space being free of solid or sealant material, or of a liquid or paste which solidify       
 
         [0063]    The solution according to the invention succeeds in establishing pressure inside isolation devices, substantially equal to that which allows fracking of the rock, without the concern of collapsing and sealing leaks. Also, the solution according to the invention does not affect the general structure of pipe equipped with known isolation devices. 
         [0064]    According to other advantageous non-limiting characteristics:
       said communication passage consists of at least one orifice presented by the wall of said first metallic sleeve and which terminates in the part of said space which extends between the two sleeves;   said communication passage consists of at least one orifice located between two of the opposite ends of the sleeves and which terminates in the part of said space between the two sleeves;   said opening presented by the wall of the pipe terminates in the part of said space located between the pipe and the second sleeve;   said communication passage between the exterior of the first sleeve and said space consists of at least one orifice located between the pipe and the end in front of said second sleeve and terminates in the part of said space located between the pipe and the inner sleeve;   said opening presented by the wall of the pipe terminates in the part of said space which extends between the two sleeves;   said opening of the pipe communicates with said space via an annular space which extends between the first ends opposite the first sleeve and the second sleeve;   said second sleeve is made of material capable of plastic deformation, such as metal and/or elastically deformable material such as rubber or material based on rubber;   the external face of the sleeve is provided, at least in said intermediate part, with an elastically deformable sealing cover, for example made of rubber;   it comprises a non-deformable ring which envelops, over a fraction of its length, said first sleeve and which at least partially limit its expansion and that of the second sleeve;   the external face of the pipe comprises, opposite said at least one communication opening between the pipe and said space, an elastically deformable cover,   said at least one opening extends opposite a connecting skirt of the first sleeve on said pipe;   said at least one opening extends opposite said non-deformable ring;   at least one end of said sleeves is capable of moving longitudinally relative to the pipe.       
 
         [0078]    Other characteristics and advantages of the present invention will emerge from the following detailed description of some preferred embodiments. This description will be given in reference to the attached drawings, in which: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0079]      FIG. 1  shows, as indicated hereinabove, a portion of pipe according to the prior art and given that, visually, that of the present invention has substantially the same appearance; 
           [0080]      FIG. 2  is, as explained hereinabove, a sectional view of part of pipe intended to illustrate methods used to date; 
           [0081]      FIG. 3  is a semi-view, in longitudinal and extremely simplified section, of a first embodiment of the invention; 
           [0082]      FIG. 4  is a more detailed sectional view, according to a longitudinal plan of the embodiment of  FIG. 3 ; 
           [0083]      FIG. 5  is an enlarged view of the part of  FIG. 4  shown in the form of a rectangle; 
           [0084]      FIGS. 6 ,  7  and  8  are views of the portion of pipe in different states which are a function of the pressure and nature of fluids circulating in the pipe; 
           [0085]      FIGS. 9 and 10  are views similar to  FIG. 3  of other embodiments; 
           [0086]      FIG. 11  is a more detailed view, in longitudinal section, of the embodiment of  FIG. 10 ; 
           [0087]      FIGS. 12 and 14  are views of opposite ends of the metallic sleeve of the embodiment of  FIG. 10 ; 
           [0088]      FIG. 13  is a view of another step relative to utilisation of this pipe; 
           [0089]      FIG. 15  is a three-dimensional view of another particular embodiment of the pipe; 
           [0090]      FIGS. 16 and 17  represent both a portion of this pipe of longitudinal sectional view and respectively a view of a detail of this portion, specifically that which is enclosed by an oval in  FIG. 15 ; 
           [0091]      FIG. 18  finally is a view of a variant of the embodiment of  FIG. 17 . 
       
    
    
     DETAILED DESCRIPTION 
       [0092]    In reference to  FIGS. 3 and 4  (in which the same reference numerals designate the same items), only a portion of pipe  1  in place in a well A is illustrated, and the portion of pipe which is provided with the isolation device referenced N−1 in  FIG. 2  is illustrated in particular. 
         [0093]    It is illustrated expanded in  FIG. 3  and not expanded in  FIG. 4 . 
         [0094]    As illustrated in  FIG. 3 , the device isolates an annular part of the well where high pressure HP prevails (hereinbelow designated P 2 ) from another annular part, located downstream, where low pressure BP (hereinbelow designated P o ) prevails. 
         [0095]    More particularly in reference to  FIG. 4  and as is well known, this tubular pipe is provided along its external face with a metallic sleeve  20  whereof the opposite ends X 20  are solid with the external face of this pipe. 
         [0096]    More precisely, these ends are enclosed inside reinforced annular rings referenced  21  in  FIG. 4 . 
         [0097]    In referring more particularly to  FIG. 5 , it is evident that the external face of the metallic tubular sleeve  20  is provided with a grooved cover  201 , for example made of rubber, capable of boosting sealing of the sleeve when the latter is deformed and is compressed against the well A. 
         [0098]    It is evident more particularly from  FIGS. 3 and 5  that there is at least one orifice  200  through the thickness of the wall of the sleeve  20 ; its function will be explained later. 
         [0099]    According to a particular characteristic of the invention, this is about a second sleeve  22 , also expandable, whereof the ends X 22  are sandwiched between those of the first sleeve  20  and the external face of the pipe  1 , as shown in  FIGS. 4 and 5 . 
         [0100]    In the case illustrated here, the two sleeves are made of ductile metallic material. However, the second internal sleeve  22  could be made of another expandable material such as an elastically deformable material based on rubber. 
         [0101]      FIG. 5  shows that the ends X 22  of the second internal sleeve  22  are located under part of the wall of the first external sleeve  20 , the latter exhibiting greater length longitudinally. 
         [0102]    These sleeves are fixed to the wall of the pipe  1  by welds. 
         [0103]    The same applies to the two parts  210  and  212  which constitute respectively the body and the end of the skirt or reinforcing ring  21 . 
         [0104]    Fixing means other than welds can be used, of course. 
         [0105]    More particularly in reference to  FIGS. 6 to 8 , there will now be a description of how such an isolation device of part of a well is used. 
         [0106]      FIG. 6  shows a situation in which the openings  3  of the pipe  1  are closed and a fluid under preset pressure P 1  is injected in the direction of the arrow v. This pressure is calculated to allow deformation of the first external sleeve  20  beyond its elastic limit, and can be of the order of 550 Bar (around 8000 psi). 
         [0107]    In the process, the fluid enters the space E which is delimited by the wall of the pipe  1 , the first external sleeve  20  and its ends X 20 . 
         [0108]    This space E is divided into two parts, in this case a space E 1  delimited by the pipe  1  and the second sleeve  22 , and a space E 2  delimited by the two sleeves. 
         [0109]    In any case, according to the invention, the space E (i.e spaces E 1  and E 2 ) is not intended to be filled with a solid material or a liquid or paste material which becomes solid thereafter, or with a sealant material. 
         [0110]    The second sleeve  22  has expansion pressure which is less than or equal to P 1 , that is, it is capable of expanding under the effect of pressure less than or equal to P 1 . 
         [0111]    Because the second internal sleeve  22  is sandwiched in between the first sleeve  20  and the pipe  1 , the second sleeve  22  deforms and is pressed against the inner face of the first sleeve  20 . 
         [0112]    Under the effect of the pressure P 1 , the sleeves  20  and  22  deform therefore simultaneously radially towards the exterior, as shown in  FIG. 6 , and the first sleeve  20  is pressed against the well. 
         [0113]    After expansion of the sleeves, the pressure drops and returns to P 0 . This pressure P 0  is applied therefore in the space E 1  located between the pipe  1  and the second inner sleeve  22 . At this instant E 1  is substantially equal to E, approximately the thickness of the second sleeve  22 . 
         [0114]    This is the situation of  FIG. 6 . 
         [0115]    In a later step, the openings  3  are cleared and a fluid under fracking pressure P 2 , above P 0  (and P 1 ), is circulated in the pipe  1 . 
         [0116]    This fluid therefore occupies the annular space B which separates both adjacent isolation devices and, as shown in  FIG. 7 , the prevailing pressure P 2  is communicated inside the space E via the orifices  200  presented by the external sleeve  20 . 
         [0117]    In this way, the space E 1  which is located between the pipe  1  and the second sleeve  22  sees its volume reduce gradually since said pressure is sufficient to deform this second sleeve and press it progressively against the pipe  1 . There is progressive transition from the situation of  FIG. 6  to that of  FIG. 8 . 
         [0118]    In the process, on either side of the first external sleeve  20 , the same equalised pressure P 2  is obtained. In these conditions, sealing is retained and the risk of collapse of the sleeve is no longer there. 
         [0119]    This solution is particularly advantageous since no mobile mechanical member is necessary. The only necessary step is to provide a second sleeve  22  and orifices  200  in the first sleeve  20 . 
         [0120]    The embodiment illustrated highly schematically in  FIG. 9  relates substantially to the same structure as that described previously if the only difference is the orifice  200  (or the orifices) not being located in the wall of the sleeve  20 , but between one of the two ends opposite sleeves  20  and  22 . 
         [0121]    However, the operation described hereinabove applies also for this embodiment, if the only difference is the pressure P 2  being initiated between the two sleeves via the abovementioned orifice(s) located between the ends of the two sleeves. 
         [0122]    The embodiment illustrated in  FIGS. 10 to 14  also deals with a structure having two sleeves  20  and  22 . 
         [0123]    However, the external sleeve  20  is devoid of orifices  200 . 
         [0124]    However, the openings  10  which connect the pipe  1  with the abovementioned space E communicate with the latter via an annular gap j 1  which extends between the first end of the first sleeve  20  and the first end of the second sleeve  22 . This is particularly evident in  FIGS. 10 and 12 . 
         [0125]    To do this, the sleeve  20  has been previously deformed locally to release such a gap. 
         [0126]    Under the effect of the introduction of initial pressurised fluid P 1  to the pipe, the openings  3  being closed, the fluid infiltrates via the openings  10  and travels in the annular gap j 1  to occupy the space E 2  located between the two sleeves  20  and  22 , as in the configuration of  FIG. 11 . 
         [0127]    In reference to  FIG. 14 , it is evident, at the other end of the sleeves, that the reinforcing ring or skirt  21  is not sealed tightly, and for this reason has an opening  213 . However, the corresponding ends X 20  and X 22  of the two sleeves  20  and  22  are jointed together and welded to the body  210  of the skirt  211 . But this leaves a gap j 2  between the inner face of the second sleeve  22  and the wall of the pipe  1 . 
         [0128]    In these conditions, the fluid of pressure less than or equal to P 2  can travel in the gap j 2  and deform the second sleeve  22  which is applied tightly against the first sleeve  20 . 
         [0129]    This gives the configuration of  FIG. 13  where there is equalising pressure P 2  inside and outside the isolation device. 
         [0130]    In this way, any risk of even partial collapsing of the device  2  is guaranteed. 
         [0131]      FIG. 15  illustrates a variant of pipe whereof the two isolation devices  2  are each provided with a non-deformable ring  6 , which partially and locally limits the expansion of the sleeves  20  and  22 . 
         [0132]    As is shown more particularly by the sectional view of  FIG. 16 , this ring  6  is located opposite the zone where the pipe is provided with communication openings  10  between the interior of the pipe  1  and the space E. 
         [0133]    According to an advantageous characteristic of the present invention, the external face of the pipe  1  comprises a deformable elastic cover  7 , for example made of rubber which covers the openings  10 . 
         [0134]    This can be a single and same tubular piece which covers all the openings  10  or several different pieces each covering an opening. 
         [0135]    This cover is attached only at some points to the sleeve, for example by adhesion. So when this relates to a pressure flow directing openings  10  in the direction of the cover  7 , the latter releases the pressure in the regions where it is not attached to the pipe  1 . 
         [0136]    The external sleeve  20  presented here is of the same type as that of  FIG. 3  and following, such that it comprises at least one through orifice  200 . 
         [0137]    As is evident earlier, when the pressure P 2  enters the space E 2  collapsing of the sleeve  22  occurs. 
         [0138]    During this collapsing, folds generated in the material of the sleeve can constitute mechanical weak zones and sources of leaks. 
         [0139]    But if the device according to the invention is reused several times, the expansion and collapsing phases of the sleeve  22  risk making it defective. 
         [0140]    In the embodiment of  FIG. 18 , the openings  10  and their associated cover  7  are located in the region of the ends of the sleeves  20  and  22 . In this way, in this region and under the effect of P 2 , the sleeve  22  diminishes slightly in diameter and exerts pressure on the cover  7 , accordingly closing the openings  10 . 
         [0141]    The pressure P 2  is applied in the space E 1  which further still limits the risk of collapsing. 
         [0142]    Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.