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You are an expert at summarizing long articles. Proceed to summarize the following text: 
FIELD OF THE INVENTION 
   The present invention relates to a method for placing an oilwell equipped or not with a defective subsurface safety valve under safe conditions. 
   It is well-known that, for safety reasons, oilwells are generally equipped with subsurface safety valves which are either interposed between the connection of two tubing elements or inserted in a nipple housed in the production tubing of the well at a depth of some ten or hundred meters. The function of these valves is to allow to automatically stop effluent production if an operating trouble occurs at the wellhead or downstream therefrom. They are often controlled from the surface by a hydraulic pressure on the opening side and they automatically close by means of a powerful return spring when a hydraulic pressure drop, whether controlled or accidental, appears on the control line. 
   The hydraulic control line can also have defects (leakage, clogged or broken line), in which case the safety valve can no longer fulfil its function. It generally remains closed under the action of its spring and shuts off the effluent passage. 
   BACKGROUND OF THE INVENTION 
   Operators currently have two solutions to overcome this deficiency. They can withdraw the safety valve from the production tubing (after setting an air lock at the wellhead) and then close the defective control line by setting in the tubing an isolating sleeve provided with packers which isolate the control fluid arrival through the nipple. The well can produce again but it is then outside the safety standards since it is no longer equipped with a subsurface safety valve. Another solution allowing to avoid this off-standard operation consists in “killing” the well, i.e. in balancing the pressure of the reservoir with a hydrostatic mud column of suitable density, then in carrying out servicing operations in the well to repair according to the techniques used in the trade. This solution, which afterwards allows to work according to the safety standards, is extremely heavy and expensive. 
   Document FR-2,734,863 describes a method and a device allowing to restore well safety by setting, according to the standards in use in the trade, a special safety valve. However, the technique according to this document requires running out the defective subsurface valve and re-using its nipple for installing the special valve. The method thus requires a precise depth for fastening the new valve, considering the re-use of the nipple for its locking system and sealing. 
   The present invention relates to a well safety valve comprising improvements in relation to the special valve and the tools as described in the aforementioned document FR-2,734,863. The present valve according to the invention can be set directly in the inner space of a production tubing of known inside diameter, without requiring an adapted nipple. Thus, the length of the connecting rods between the valve and the wellhead at the surface no longer has to be adjusted. 
   SUMMARY OF THE INVENTION 
   The present invention thus relates to a well safety valve set in a production tubing, comprising a body comprising shutoff means for shutting off a passage inside the body, anchor means for anchoring the body in the tubing, sealing means between the body and a wall of the tubing, the valve comprising communication means for a hydraulic pressure between the valve and the surface of the well. According to the invention, the shutoff, anchor and sealing means comprise hydraulic activation means such that the hydraulic pressure transmitted from the surface activates the means so as to open said passage, anchor the valve in the tubing and activate the sealing means on the wall of the tubing. 
   The shutoff means can comprise a shutoff valve held in closed position by a return means, a hydraulic piston providing under pressure longitudinal displacement of a sleeve so as to hold the shutoff valve open. 
   The anchor means can comprise rams that can be displaced radially against the tubing wall by an anchor sleeve of a hydraulic piston. 
   The anchor means can be mechanically locked by immobilization means of the anchor sleeve. 
   The sealing means can include a pile of several ring-type joints made of a resilient material which can be compressed by the displacement of a compression sleeve of a hydraulic piston. 
   The section of the ring-type joints can be V-shaped with an unsymmetrical shape of the branches of the V, the branch in inner contact with the body of the valve being the shorter, the branch in contact with the tubing wall, after compression of the pile by the piston, is deformed to come into contact with the tubing wall. 
   The pile can comprise a metal anti-extrusion cup whose outside diameter is approximately the outside diameter of the valve body before compression of the pile. 
   The pile can consist of eight V-shaped cups made of HNBR type elastomer of Shore hardness A of about 80. 
   The pile can be mechanically held compressed by immobilization means of the compression sleeve. 
   The hydraulic communication means can consist of tubular elements assembled by connections, one end of a first element is connected to the body of said valve, one end of the upper element is connected to a hanger element. 
   The hanger element can be held in an adapter fastened to the wellhead and comprising hydraulic communication means with said tubular elements. 
   The adapter can include radial-displacement rams intended to close on said tubular elements. 
   The invention also relates to a method of setting the valve according to the invention in a production tubing, comprising the following stages: 
   assembling an adapter on the wellhead, 
   lowering the valve into the tubing by assembling a number of tubular elements corresponding to the desired depth, 
   suspending the valve and its tubular elements from the adapter by means of a hanger and connecting the hydraulic line of said tubular elements to a source of pressure at the surface, 
   placing the valve under pressure so as to open the passage, anchor the body of the valve in the tubing at the depth at which it has been lowered and compress the pile of joints to obtain annular sealing. 
   According to the method, the well can be placed under safe conditions by decreasing the pressure in the valve so as to close said passage shutoff means without unlocking the anchor means or deactivating the pile of seal joints. 
   The tubular elements can be disconnected and pulled out of the hole before lowering a tool suited to be connected to the top of the valve body and to unlock by jarring the anchor means and the pile compression means. 

   
     BRIEF DESCRIPTION OF THE FIGURES 
     Other features and advantages of the present invention will be clear from reading the description hereafter, given by way of non limitative example, with reference to the accompanying drawings wherein: 
       FIGS. 1A and 1B  diagrammatically show a valve according to the prior art, 
       FIGS. 2A and 2B  diagrammatically show an installation comprising a valve according to the present invention, 
       FIG. 3  is a lengthwise section of an embodiment of a valve according to the invention, 
       FIGS. 4A and 4B  diagrammatically show the principle of the sealing and anchor means of the valve according to the invention. 
   

   DETAILED DESCRIPTION 
     FIG. 1A  shows an oilwell  1  equipped with a subsurface safety valve  2  whose hydraulic control line  3  is defective. The well comprises a production tubing  4  communicating with a Christmas tree  5 . This safety valve is positioned in a nipple  6 . In order to repair the well and to bring it into conformity with standards, the valve has to be removed from its seat to set a new valve allowing to restore production as soon as possible, and in complete safety. If the control line is no longer operational, a safety valve can be set in seat or nipple  6 , a valve such as the valve described in document FR-2,734,863 mentioned here by way of reference. 
     FIG. 1B  shows this valve consisting of three main assemblies 
   shutoff assembly  7 , or the valve proper, controlled by hydraulic pressure, 
   the assembly consisting of adapter and connecting flanges  8 , 
   the assembly consisting of connecting lines  9  between this adapter  8  and valve  7 . 
   The details of these equipments and of the setting or operating procedures are clearly described in the aforementioned document. Considering the length fixed between the nipple and the position of adapter element  8 , the number of rods  9  and their total length have to be determined according to the well considered. 
     FIG. 2A  shows a well  11  comprising a tubing  10  of known inside diameter. If it is necessary to add a safety valve inside this tubing, the system according to the invention, diagrammatically shown in  FIG. 2B , can be advantageously used. An adapter  12  is interposed between master valves  13  and the tubing hanger. This device is similar to the one described in document FR-2,734,863 in that it has at least two functions: suspension of control rods  14  by means of lower lateral screws  50  and seal around hanger  21  so as to communicate with an outside hydraulic control line  15 . However, according to the present variant, adapter  12  is also provided with two rams  51   a  and  51   b  allowing to manoeuvre the valve and the rod elements in the tubing. Thus, suspension and fastening of the rods is performed by tightening the rams on the rods. Control rods  14  can also be the rods used in the prior art. They can consist of a tubular element having a maximum length of approximately 6 meters and equipped at the end thereof with quick pin-to-box connections so as to be connected between elements. One of the rods is equipped with an expansion element or connection  16  for taking up the length variation of the whole of the rods, considering the possible temperature variations. Valve  17  comprises the following functional means: 
   shutoff means  18  for shutting off the inner channel of the valve body, 
   anchor means  19  for anchoring valve  17  in tubing  10 , 
   sealing means  20  between the valve body and the inside of tubing  10 . 
   In a variant, there are two anchor stages, in another variant, a single stage is necessary. 
   The valve is lowered after fitting the hanger element of tubing  10  with an adapter  12  which is used to suspend the whole of the system once it has been entirely lowered in the well, to maintain the connecting elements one after the other, to allow connection between them, and to lower the assembly stage after stage. The well being under pressure, an air lock mounted on the Christmas tree allows the procedure to be carried out in the well. This procedure is conventionally performed by means of a wireline. It consists in lowering the valve and the connecting elements in several stages. Stage 1: the valve hanging from its first rod element  14  is lowered until the upper part of the first element is held by the rams, thus allowing suspension and fastening of the first element on adapter  12 . Stage 2: the standard rod element is lowered and connected to the first element hanging from adapter  12 . The rams are then opened to allow descent of the first element fastened to the second rod element until the upper part of the standard element is held by the rams, thus allowing suspension and fastening of its two elements on adapter  12 . Stage 3: this stage 3 is similar to stage 2 and multiplied as many times as necessary according to the number of rods required, considering the depth at which the valve is arranged. Last stage: this last stage consists in lowering the last element comprising, in the upper part thereof, hanger  21  and in connecting it to the last standard element held by the rams. The rams are then opened, thus allowing descent of the entire assembly and setting thereof, as well as locking of hanger  21  in adapter  12 . 
   When a hydraulic pressure is applied in control line  15 , the various functional means of valve  17  are activated, i.e. the valve opens after tilting of shutoff valve  18 , anchor dogs  19  are expanded radially to immobilize the valve body in the tubing, the packer is compressed to rest against the tubing wall and form a seal. 
     FIG. 3  shows, in sectional view, more details of the make-up of safety valve  17 . Shutoff valve  18  is in closed position under the action of a spring (not shown). It is opened by displacement of a tube  23  under the thrust action of a ring  24  connected to a piston  25 . In the presence of a sufficient hydraulic pressure in chamber  26 , the piston is pressed against tube  23  by means of ring  24  until it compresses spring  27  and causes said tube to slide, which causes disk  18  to tilt. In the absence of pressure in chamber  26 , return spring  27  pushes tube  23  back and the disk closes, thus restoring well safety. 
   Anchor dogs  19  are displaced radially by a piston  28  whose end has the shape of a cone on which said anchor dogs  19  rest. Piston  28  is pushed under the anchor dogs by the hydraulic pressure in chamber  29 , the displacement of the piston blocking the anchor dogs on the wall of tubing  10 . Means  30  for locking the position of anchor piston  28  allow this piston to be held in place even when the pressure has dropped in chamber  30 . These locking means can work according to the principle of a dog stop or of teeth.  FIG. 3  shows a second assembly: anchor dogs  19   a , piston  28   a , hydraulic chamber  29   a , locking means  30   a , in the upper part of the body of the pump. However, the invention is not limited to two anchor assemblies, and in most embodiments a single anchor assembly is necessary. 
   The present valve also comprises sealing means between the body of the valve and tubing  10 . This assembly is an essential element insofar as, in case of failure, the safety valve is totally inoperative and it is delicate to form a seal on a raw surface such as the wall of a tubing. These sealing means include a packing assembly  20  which is activated on the tubing wall by a piston  31  displaced by the hydraulic pressure present in chamber  32 . Locking means  33  hold piston  31  in place even without pressure in chamber  32 . 
   A line  34  communicating with a connector  22  distributes the hydraulic pressure in the chambers described above: valve opening chamber  26 , anchor chamber(s)  29  and  29   a , sealing means chamber  32 . Connector  22  is connected to the surface by rods  14  ( FIG. 2B ). It can be noted that the hydraulic pressure rise in line  34  (approximately 35 MPa) transmits the pressure energy in all the chambers simultaneously, which provides substantially at the same time: opening of the valve, anchoring and sealing thereof in the tubing. When the hydraulic pressure drops in line  34 , the valve closes but remains in position, anchored and sealed. A special profile  35  arranged at the top of the valve body allows to disanchor the valve body by traction and jarring by means of a fishing tool suited to this profile. By jarring on the valve body, a series of shear pins are broken, thus releasing anchor piston(s)  28 ,  28   a , as well as sealing piston  31 . The released valve can then be pulled up to the surface. 
     FIGS. 4A and 4B  diagrammatically illustrate the principle of packing assembly  20  of the sealing means between packer holder  36  and tubing  10 . Reference (j) designates the radial play between the outside diameter of packers  37  and the inside diameter of the tubing. This play is generally of the order of 2.5 mm, but it may reach 5 mm. The packing consists of a pile of eight cups  38  of optimized shape to withstand the pressure after being deformed against the tubing wall. Part  40  is the support against which the pile of cups  38  is compressed in a thrust load. Part  41  designates the nose of the piston (reference number  31  in  FIG. 3 ). An anti-extrusion cup  39  is interposed between the first cup and piston nose  41 . It can be noted that the pressure of the well applies in the direction shown by arrow  42 . 
   The optimized shape of cups  38  results from the general herringbone U or V shape wherein the section of the cups exhibits a symmetry along an axis parallel to the central axis (one can refer to the technical handbook: “Seals and Sealing Handbook”—Ed. The Trade and Technical Press Limited, 1985). These seals are suitable for mounting without clearance adjustment, or of some tenths of a millimeter only. In fact, it has been verified that joints having sections with an axis of symmetry are not compatible with large clearance adjustments, for example above 2.5 mm, in particular in case of resistance to a pressure above 5000 PSI, i.e. about 350 MPa. 
   For a packer to be able to take up a clearance of some millimeters, it has been determined that the following notably have to be optimized: the deformation capacity of the material, the pressure resistance of this material, the level of the frictions on the packer holder so that the necessary deformations are obtained with lesser stresses. 
     FIG. 4B  diagrammatically illustrates the whole of the packer once compressed by the action of piston  41 . The inner part of the pile of cups forms a seal on the surface  43  of packer holder  36 . Metallic anti-extrusion cup  39  deforms and presses against inner wall  44  of the tubing. The outer lip of the cups is raised to also rest on the tubing and close the annular space. Under pressure, as shown by arrow  42 , the packers lean more heavily against the tubing while being held by the anti-extrusion cup. 
   The optimized shape of the sealing cups can be defined as follows: the section of the cup has the shape of a V one branch of which, in contact with the surface of the packer holder (inside diameter of the cup), is shorter  47 . Thus, point  45  of the V is no longer in the median position of the annular space between the packer holder cylinder and the inner wall of the tubing, but it is offset and closer to the packer holder. Branch  46  of the V, which undergoes the most deformation, and which is on the side of play j, is the longer, which favours its displacement under the action of the piston. The shape of the end of the two branches of the unsymmetrical herringbone is suited to efficiently press against the cylindrical surfaces of the packer holder and of the tubing. Experience and finite-element calculations have shown that this unsymmetrical shape of the cups provides the most regular contact stresses and therefore good pressure resistance. 
   The material used can be HNBR rubber of Shore A hardness 80, which is also suited for standard temperatures in production wells. 
   According to the invention, the number of cups selected is eight in the case of a valve suited to be lowered into a tubing whose inside diameter is approximately 75 to 80 mm. The invention is not limited to this number of cups, which can vary depending on the operating pressure and/or on the nature of the fluids.

Summary:
The present invention relates to a well safety valve set in a production tubing, comprising a body ( 17 ) including shutoff means ( 18 ) for shutting off a passage inside the body, anchor means ( 19 ) for anchoring the body in the tubing, sealing means ( 20 ) between the body and the wall of the tubing, the valve comprising communication means ( 14 ) for a hydraulic pressure between the valve and the surface of the well. According to the invention, the shutoff, anchor and sealing means include hydraulic activation means such that the hydraulic pressure transmitted from the surface activates the means so as to open the passage, anchor the valve in the tubing and activate the sealing means on the wall of the tubing. 
     The invention also relates to a method for setting the valve.